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Diatoms: A fossil fuel of the future
Abstract
Long-term global climate change, caused by burning petroleum and other fossil fuels, has motivated an urgent need to develop renewable, carbon-neutral, economically viable alternatives to displace petroleum using existing infrastructure. Algal feedstocks are promising candidate replacements as a 'drop-in' fuel. Here, we focus on a specific algal taxon, diatoms, to become the fossil fuel of the future. We summarize past attempts to obtain suitable diatom strains, propose future directions for their genetic manipulation, and offer biotechnological pathways to improve yield. We calculate that the yields obtained by using diatoms as a production platform are theoretically sufficient to satisfy the total oil consumption of the US, using between 3 and 5% of its land area.
... Diatoms can accumulate high TAG concentrations under silicon limitation, avoiding the deleterious effects on photosynthesis, gene expression and protein content associated with N limitation [13]. Furthermore, it is well known that TAG accumulation in diatoms growing in batch cultures under controlled environmental conditions occurs naturally in the stationary growth phase [14]. However, TAG accumulation in diatoms growing in open ponds is more susceptible to climatic conditions [15,16]. ...
... In general, TAG accumulation in microalgae coincides with a decrease in growth, which may be due to cell aging or stress caused by nutrient deficiency [38,39]. Diatoms alter their biosynthetic pathways for the production of neutral lipids in response to culture age [40], silicon deficiency [13,14,41], nitrogen depletion [13,14,42] and variations in medium salinity [43]. The summer-cultures showed faster TAG accumulation than the spring-cultures, though no cell aging or decay phase was observed. ...
... In general, TAG accumulation in microalgae coincides with a decrease in growth, which may be due to cell aging or stress caused by nutrient deficiency [38,39]. Diatoms alter their biosynthetic pathways for the production of neutral lipids in response to culture age [40], silicon deficiency [13,14,41], nitrogen depletion [13,14,42] and variations in medium salinity [43]. The summer-cultures showed faster TAG accumulation than the spring-cultures, though no cell aging or decay phase was observed. ...
... Despite its importance, many countries still rely on fossil energy sources such as oil, coal, and natural gas [2], which negatively impact natural resources and ecosystems. Levitan et al. [3] suggest that increasing the use of renewable energy can mitigate these ecological consequences and reduce dependence on imported fossil fuels. Renewable energy includes solar, wind, bioenergy, geothermal, hydropower, and ocean energy [4], which can improve environmental quality by producing minimal greenhouse gas emissions [5]. ...
... Generalized Least Squares method (GLS) 3 Das et al. [54] Measure renewable energy intensity and examine its impact on the export performance of Indian manufacturing firms System dynamic panel estimation and fixed effects 4 Dzwigol et al. [55] Investigate the nonlinear impact of environmental regulations, the effect of extending renewable energies, and the growth of energy efficiency on a country's green economic growth ...
This study employs a Systematic Literature Review (SLR) combined with bibliometric and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodologies to investigate the factors influencing the use of renewable energy in enhancing firm performance. An analysis of 27 selected articles reveals three key factors: firm innovation, governance, and regulation. The study further emphasizes the benefits of renewable energy adoption across various business performance metrics, including firm profit, financial, logistics, and sustainable performance. The novelty of this paper lies in its comprehensive integration of bibliometrics analysis with PRISMA to bridge gaps in existing literature. It contributes to the field by offering insights into the complex relationship between renewable energy use and firm performance, underscoring the significance of continued investigation to resolve inconsistencies and deepen understanding.
... Одной из основных мер по предотвращению вышеуказанной проблемы является поиск возобновляемых альтернативных источников энергии [6]. Невозобновляемые источники энергии обладают высокой стоимостью, что делает переход на альтернативную энергию важным этапом для обеспечения энергетической безопасности и удовлетворения высокого спроса на энергию [2]. ...
... 4,4 ± 0,3 4,5 ± 0,2 5,5 ± 0,1 6 3,2 ± 0,8 3,8 ± 0,4 4,5 ± 0,4 7 2,1 ± 0,1 2,5 ± 0,1 3,1 ± 0,2 Таблица 4. Каталазная активность изолятов Geobacter, Thermomonas и Rhodopseudomonas Table 4. Catalase activity of Geobacter, Thermomonas, and Rhodopseudomonas isolates Время культивирования, ч Geobacter Thermomonas Rhodopseudomonas 0 ...
Traditional energy sources pollute the environment. Microbial fuel cells are an alternative energy source that can reduce the environmental burden. Microbial fuel cells also remove recalcitrant wastes from wastewater. This research featured the enzymatic potential of microbial isolates obtained from the Abakan Arzhan thermal spring. The study involved isolates of the genera Geobacter, Thermomonas, and Rhodopseudomonas. The keratinolytic analysis was in line with State Standard R 55987-2014. The chitinolytic activity was determined by injecting a bacterial suspension on Petri dishes with a chitin-containing medium. The lipolytic analysis involved cultivating the isolates in Stern’s glycerol fuchsin broth. The xylan hydrolysis depended on the reducing sugars. The cellulase activity was measured according to the standard method recom mended by the International Union of Pure and Applied Chemistry (IUPAC). The catalase potential was evaluated by the gasometric method on 1% gasoline media. The optimal parameters of consortium cultivation were determined by the voltage generated. The Geobacter isolate had the maximal keratinolytic activity while the Thermomonas isolate demonstrated the maximal protein hydrolysis (80.1 ± 1.5%). Both Geobacter and Rhodopseudomonas showed good lytic activity against chitin with the lysis zone of ≥ 3 mm. The Geobacter isolate demonstrated as many as 350 units of xylanase activity and 365 units of cellulase activity; Ther momonas had 350 units of xylanase activity and 360 units of cellulase activity; Rhodopseudomonas showed 310 units of xylanase activity and 304 units of cellulase activity. The maximal catalase properties belonged to Geobacter (1.40 units) and Thermomonas (1.38 units). The maximal energy generation by bacterial consortia occurred at pH 8 and 45°C after 48 h of cultivation. In this research, isolates of the genera Geobacter, Thermomonas, and Rhodopseudomonas from the Abakan Arzhan thermal spring were able to remove recalcitrant components, thus demonstrating good prospects for biological treatment of industrial wastewater.
... Now, sustainable energy sources are expected to be utilized to increase the ratio of carbon-neutral energy for industries that rely on fossil resources in order to face up to the global issues caused by the anthropogenic CO 2 emission. Biomass of oleaginous microalgae has been considered a promising feedstock for the production of biofuels due to the fact that it does not compete with food production and enables higher biomass productivity than that of cellulosebased biomass (Maeda et al. 2018;Levitan et al. 2014). To achieve a high yield of biomass production, particularly in an outdoor cultivation, culture conditions need to be optimized for the oil accumulation in each algal species, inasmuch as the metabolisms related to oil accumulation in microalgae strongly depend on the physiological states of photosynthesis under changing environmental situations. ...
... JPCC CTDA0820 (hereafter Mayamaea sp.). Diatoms are highly diverse with an estimate of > 100,000 species (Mann and Vanormelingen 2013) and play a major role in primary production at a global scale, resulting in 40% of total oceanic productivity which corresponds to 20% of carbon fixation on the earth (Levitan et al. 2014). They are evolutionarily distinct and develop the unique structures and metabolisms in the cells through secondary endosymbiotic events (Falkowski et al. 2004). ...
Highly oil-accumulative diatoms are expected to be a promising biomass for the production of biofuel. To harvest the diatom oils at high yields, it is critical to elucidate the relationship of oil accumulation with photosynthesis under fluctuating environmental conditions. Here, we characterized the physiological responses of the growth and photosynthesis in the mesophilic diatom Fistulifera solaris and the cold-tolerant one Mayamaea sp. JPCC CTDA0820 to nitrogen starvation, one of the most notable abiotic stresses, where most eukaryotic algae decrease their photosynthetic activity and accumulate oil in the cells. While F. solaris started showing growth retardation at NaNO3 levels less than 50% of a normal F/2 artificial seawater (ASW) medium, Mayamaea sp. sustained normal growth even at a NaNO3 level 10% of normal F/2ASW, indicating the sharp contrast of nitrogen requirement between these two diatom species. In the transition from 100 to 0% nitrogen conditions in the modified F/2ASW, F. solaris showed a clear suppression of chlorophyll (Chl)-based photosynthetic O2 evolution rate and relative electron transport rate at photosystem II, which were negatively correlated to the capacity of non-photochemical quenching. Meanwhile, there was no change in these Chl-based parameters observed in nitrogen-starved Mayamaea sp. Instead, Mayamaea sp. showed a significant decrease in the Chl a amount per cells. These data suggested the occurrence of two types of photosynthetic responses to nitrogen starvation in oleaginous diatoms; that is, (1) suppression of photosynthetic activity per Chl with enhancing heat dissipation of excess light energy and (2) synchronous suppression of cellular photosynthetic activity with Chl amounts.
... The close-out report on ASP identified 50 species out of the complete set of isolated algae to be better lipid accumulators, out of which 60% were diatoms. These numbers best describe the importance of diatoms, among other microalgae, as a significant source of lipids for biodiesel production [11][12][13]. ...
... Analogous to microalgal cultivation, diatom cultivation has been demonstrated planktonically (as cell suspensions in culture medium) in open ponds and closed photobioreactors for more than 50 years [11]. However, the past decade witnessed significant efforts towards biofilm-based microalgae cultivation [19]. ...
The rapidly depleting fossil fuel reserves with rising greenhouse gas levels (GHGs) in the atmosphere necessitate exploring alternate sustainable energy options. Biofuels from microalgae are emerging as a viable renewable energy resource owing to their inherent characteristics of higher biomass and lipid yield per hectare compared to other terrestrial bioenergy feedstocks. In this context, the present communication highlights the prospects of microalgal biofuel and other value-added products produced in a decentralized microalgal biorefinery in the flood plains (gazani lands) of the west coast of India. The spatial extent of potential sites for diatom cultivation estimated in three districts along the Indian west coast was 1940 ha. The opportunities for establishing biorefineries using diatoms as renewable bioenergy feedstocks were investigated through species prioritization, seasonal availability, tolerance, and biochemical composition analyses. Nitzschia and Amphora sp. were prioritized for lab-scale productivity studies based on their tolerance and macromolecular composition. When cultivated in a prototype biofilms-based bioreactor designed using gravel stones as substrates, Amphora sp. Yielded 16 times more productivity (0.56 g L⁻¹) than conventional shake flask cultures. Design of a diatom biorefinery and its mass budgeting considering 100 kg dry biomass yielded ∼15–24 kg of biodiesel. Techno-economic assessment of biodiesel with value-added products of glycerol, biogas, and biofertilizer demonstrated a biodiesel production cost of 30.08–59.52 INR/kg of biodiesel. Harvesting cost in a hybrid mode using mechanized scrubbers and manual labour was estimated as 20 INR/kg of biomass.
... P. tricornutum is an oil-producing diatom capable of synthesizing and storing significant amounts of lipids in lipid droplets, which can be converted into biodiesel, offering high commercial value (Singh and Gu 2010; Ding et al. 2023). As a result, enhancing the lipid content of P. tricornutum has become a central focus in diatom research (Levitan et al. 2014;Li et al. 2014). Previous studies have explored various approaches to increase lipid accumulation in P. tricornutum by modifying cultivation conditions. ...
Marine diatoms are highly valued commercially due to their abundant lipids and bioactive substances. Phaeodactylum tricornutum, a key oil-producing diatom, has faced challenges in large-scale cultivation, primarily due to zooplankton predation. Our previous studies identified that the Pt2015 overexpression strain (termed oeT) alters the morphotype of P. tricornutum which demonstrated a majority triradiate morphotype and conferred resistance to zooplankton. In this study, we found that under 60-L culture conditions, the oeT strain was maintained at a stable level (84%). Additionally, the growth of the oeT strain was significantly higher than that of wild type (WT), with a 10% increase in accumulated dry weight. Notably, lipid content in the oeT strain was enhanced by 13.4% relative to WT. Moreover, the contents of fatty acid such as C14:0 and C16:1 are much higher than that of WT. These results suggest that the oeT strain demonstrates considerable advantages for large-scale cultivation of P. tricornutum.
... Diatoms are important primary producers in the ocean and are highly effective in carbon sequestration, making them excellent candidates for sustainable production of biofuels (Levitan et al. 2014). P. tricornutum is a diatom and belongs to the model organism, currently possessing four GSMMs. ...
Oleaginous microorganisms have the unique ability to accumulate lipids that can exceed 20% of their dry cell weight under certain conditions. Despite their potential for efficient lipid production, the metabolic pathways involved are not yet fully understood, largely due to the complexity of intracellular processes and the challenges in phenotypic prediction. This review synthesizes the latest research on the application of Genome‐scale Metabolic Network Models (GSMMs) to study oleaginous microorganisms, including bacteria, cyanobacteria, yeast, microalgae, and fungi, and provides a comprehensive analysis of how GSMMs have been utilized to decipher the metabolic mechanisms behind lipid accumulation and to identify key genes involved in lipid synthesis. The review highlights the role of GSMMs in predicting cellular behavior, optimizing metabolic engineering strategies, and discusses the future directions and potential of GSMMs in enhancing lipid production in microorganisms. This comprehensive overview not only summarizes the current state of research but also identifies gaps and opportunities for further investigation in the field.
... The presence of highly branched isoprenoids (HBIs) in diatoms has been used as an effective environmental biological marker, for example, alkenes can be considered a useful indicator of petroleum deposits [10,92]. For instance, the ratio of steranes (28 and 29 carbon atoms) [96], 24-norcholestanes [97], and the highly branched isoprenoid (HBI) alkenes [98] detected in diatoms are also found in many oil fields around the world [99]. ...
The search for practical solutions to alleviate the destructive impact of petroleum hydrocarbons in marine environments is contributing to the implementation of prospecting strategies for indigenous microorganisms with biodegradative and bioremediation potential. The levels of petroleum contamination entering the marine environment each year have been estimated at around 1.3 million tonnes, a figure that is expected to increase by 1.9% annually over the next decade. The recent interest in decarbonizing our energy system and accelerating the clean energy transition has created a demand for greener technologies and strategies to find innovative, sustainable, and cost-effective treatments for the marine environment. Diatoms (Bacillariophyta) are one of the most diverse and successful taxa in coastal–marine environments and are a relatively untapped pool of biodiversity for biotechnological applications. Recent reports have revealed the significant presence of diatoms associated with oil spills and petroleum hydrocarbon degradation. Most diatoms can secrete substantial amounts of exopolysaccharides (EPSs) into their environment, which can act as biosurfactants that, in addition to oxygen and other enzymes produced by diatoms, create suitable conditions to enhance hydrocarbon solubility and degradation into less toxic compounds in seawater. Recent reports on the biodegradation of aliphatic and aromatic hydrocarbons by diatoms are indicative of the potential of these taxa to achieve success in the bioremediation of hydrocarbons in marine environments. This review highlights the main attributes and roles that diatoms could play in integrated strategies for biodegradation and bioremediation of petroleum hydrocarbon pollutants and as such represent a green, eco-friendly, and sustainable contribution to mitigate damage to biodiversity and value chains of marine ecosystems.
... Using fossil fuels causes greenhouse gas emissions in the atmosphere, and consequently, global warming and climate change problems arise [3]. To reduce all these problems, limiting the use of fossil fuels and transitioning to RESs are of great importance [4,5]. RESs are easily accessible, unlimited, natural, and environmentally friendly energy sources like solar, wind, and biomass. ...
The use of renewable energy sources (RESs) is increasing every day to meet increasing energy demands and reduce dependence on fossil fuels. When designing hybrid renewable energy systems (HRESs), it is necessary to examine their technical, economic, and environmental feasibility. In this study, a new strategy is proposed using the HOMER Matlab Link (ML) connection for an HRES model consisting of a photovoltaic (PV) system, a wind turbine (WT), a biogas generator (BGG), and a battery storage system (BSS) designed to meet the electrical energy needs of Doğanevler village located in the rural area of Bingöl province. The data obtained as a result of the proposed strategy (PS) are compared with HOMER’s loop charging (CC) and load following (LF) optimization results. According to the PS, the optimum capacity values for the HRES components are 10 kW for WT, 10 kW for PV, 8 kW for BGG, 12 kWh for BSS, and 12 kW for the converter. According to the optimum design, 16,205 kWh of the annual energy produced was generated by PV systems, 22,927 kWh by WTs, and 22,817 kWh by BGGs. This strategy’s NPC and LCOE (Levelized Cost of Energy) values are calculated as USD 130,673.91 and USD 0.207/kWh, respectively. For the CC dispatch strategy, the NPC and LCOE values are calculated as USD 141,892.28 and USD 0.240/kWh, while for the LF dispatch strategy, these values are USD 152,456.89 and USD 0.257/kWh. The CO2 emission value for the system using a BGG was calculated as 480 kg/year, while for the system using a DG, this value increased approximately 57 times and was calculated to be 27,709 kg/year. The results show that the PS is more economical than the other two strategies. The PS provides energy security, reduces costs, and increases environmental sustainability. Finally, a sensitivity analysis was conducted based on the availability of renewable resources, fuel cost, and inflation parameters, and the results were analyzed.
... [O. Levitan 2014].Optimization involves selecting the right nutrient sources and concentrations to support robust microbial growth and achieve high protease yield. The enhancement of protease production in microbial strains can be significantly improved through the optimization of fermentation conditions and the utilization of genetic engineering techniques. ...
... Thus, diatoms prove to be a sustainable source for biofuel production, with potential applications in a biorefinery context (Sharma et al., 2021). The entire U.S. oil demand could potentially be satisfied using only 3-5% of the country's land (Levitan et al., 2014). The Jawkai Bioengineering R&D Center has achieved sustained diatom yields, aligning with commercial biofuel production predictions (Wang & Seibert, 2017). ...
... Thanks to its peculiar shapes and interesting properties, biogenic silica diatoms shell exhibits valuable potentiality thanks to its mixed nano and microstructure which explain thousands of publications in distinct fields like marine biology, materials science, nanotechnology, optics, electronics, medicine and agriculture [11] [12] [13]. In addition, 3D nanoporous patterns of diatom frustules make it a convenient shuttle to internalize and release molecules (e.g., therapeutic agents for medical purpose) [14] and ordered porosity distribution of diatom frustule bears a similarity with photonic crystal [15]. ...
... 18,25−27 Diatoms include over 200,000 estimated species, widely distributed in diverse natural habitats where they form large biomasses during seasonal blooms that sustain the aquatic food web and primary production on Earth. 28,29 Due to their resilience, metabolic plasticity, and capacity of accumulating lipids to a greater extent than other microalgae, diatoms have been often explored as biological platforms for the production of oil and valuable products. 30−32 However, studies related to heterotrophic cultivation are quite uncommon and mainly focus on the optimization for the production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ...
Despite the theoretical high productivity, microalgae-based oil production is not economically sustainable due to the high cost of photoautotrophic cultures. Heterotrophic growth is a suitable economic alternative to overcoming light dependence and climatic/geographic fluctuations. Here we report data about growth performance, biomass production, and lipid composition of the marine diatom Cyclotella cryptica, chosen as a model strain for biodiesel production in heterothrophy. A repeated-batch process of heterotrophic cultivation has also been investigated to assess the robustness and phenotypic stability. The process consisting of six constant cycle repetitions was carried out for 42 days and led to an average dry biomass production of 1.5 ± 0.1 g L–1 of which 20% lipids composed of 60% triglycerides, 20% phospholipids. and 20% glycolipids. The major fatty acids were C16:0 (∼26%), C16:1 ω-7 (∼57%), and C20:5 ω-3 (∼12%), with a significant reduction in the unsaturated fatty acids in comparison to other microalgae grown in heterotrophy. Fatty acids were differently distributed among the glycerolipid classes, and the lipid composition was used to compare the potential properties of C. cryptica oil with traditional vegetable biofuels.
... The most abundant primary sources of EPA and DHA are the marine microalgae Nannochloropsis, Phaeodactylum, Schizochytriu, and Thraustochytrium are just a few of the autotrophically and heterotrophically cultivated microalgae that have been studied for their high EPA and/or DHA content [87]. Varied physiological situations cause different fatty acid quantities to be generated [73]. The accumulation of generated fatty acids is strongly linked to microalgae growth stages, serving as an energy reserve during adversity or cell division. ...
Omega-3 fatty acids are polyunsaturated fatty acids that are vital for human food consumption and metabolism. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two long-chain polyunsaturated fatty acids (LC-PUFAs), are primarily obtained from diatoms in the oceanic food web. Though microalgae are the main producers of EPA and DHA, but currently, only few algal strains are known to produce large levels of EPA and DHA. The demand for nutraceuticals has significantly increased because of people’s increased awareness and health consciousness. Due to foods being the concentrated supply of omega-3 PUFAs (polyunsaturated fatty acids), this has increased the demands on aquatic sources of n-3 PUFAs. Micro-algal sources must be carefully examined due to the numerous drawbacks and difficulties of fish oils and the lack of DHA and EPA in plant sources. This review focuses on the current state of omega-3 PUFA (polyunsaturated fatty acids) production, sources, and market demand to provide an overview of sources that are being explored for sustainability as well as current and anticipated market trends in the omega-3 industry. This will make it possible for them to be produced on a wide scale for the benefit of human health.
... Not only the algal species but also the growth phase (Boëchat & Giani, 2000). There is a relationship between diatoms and both CHO (r = 0.425) and LIP (r = 0.406), whereas the primary component of diatom cells is lipid, and the average lipid content in diatoms can reach 25% of dry weight (Levitan et al., 2014). Also, they produce a lot of extracellular polymeric compounds, such as glycoproteins and polysaccharides (Haynes et al., 2007). ...
The present study attempted to test the applicability of using phytoplankton as a bioindicator for assessing water quality along the Eastern Alex-andria coast, Egypt. Eight stations were selected to cover the different characteristics of seawater during the summer 2022. Six algal groups were detected in different ratios: Bacillariophyceae, Cyanophyceae, Dinophyceae, Chlorophyceae, Silicoflagellata, and Euglenophyceae. Phytoplankton abundance was found highest at the Port Said (PS) beach, and the lowest abundance was detected at Ras El Bar (RB) beach. According to the evaluation of phytoplankton abundance, all the studied stations are oligotrophic state except PS was eutrophic. Based on Chl a concentration , the selected stations could be described as good-bad from west to east. The Shannon diversity and Pielou evenness indexes classified the studied stations as being moderate pollution except for PS and RB stations. The existence of organic pollution indicators species like Navicula, Synedra, and Euglena is a warning indication of the declining water quality especially in B and M stations. The biochemical compositions of the collected phytoplankton were spatial fluctuated. Protein and carbohydrates were the dominant macromolecules in the phytoplankton community compared with lipids. These macromol-ecules are used to assess trophic states whereas the ratio between protein and carbohydrate > 1 represents a healthy coast as observed in some stations. Thus, phytoplankton should be considered a bioindicator within Water Framework Directive monitoring programs for the Mediterranean Sea. For the long-term monitoring of the Mediterranean Sea's ecosystem, it is recommended that the macromolecules of phyto-plankton should be determined.
... Also in our experiments the intensity of the red plastid autofluorescence decreased not before 96 h in ammonium-medium (Table S2B). We also observed accumulation of lipid droplets within the cells towards the end of the cultivation interval (Fig. S5), which is a typical phenotype for nitrogen starvation (Ge et al., 2014;Yang et al., 2013;Levitan et al., 2014). ...
Background. Soil microenvironmental variables showed an important key in α and β-tree diversity in Neotropical montane oak forest. Thus, understanding the microenvironment fluctuation at small-fragment effects on tree diversity is crucial in maintaining the montane oak ecosystems. In this study, we hypothesized that within a relatively small-fragment (151.63 ha), tree α and β-diversity fluctuate and specific soil microenvironmental factors could influence tree species diversity to answer three questions: Do tree α and β-diversity differ among transects, even in a short-distance between them? Do microenvironmental variables influence tree diversity composition that occurs within a relict Neotropical montane oak forest? Is there a particular microenvironmental variable influencing tree species-specific?
Methods. We established four permanent transects during a year in a relict Neotropical montane oak forest, we assessed tree diversity and specific microenvironmental variables (soil moisture, soil temperature, pH, depth litterfall and light incidence). This allowed us to evaluate how microenvironmental variables at small-fragment influence α and β-tree diversity and tree species-specific.
Results. Our results showed that α-diversity was not different among transects; however, β-diversity of tree species was mostly explained by turnover and soil moisture, soil temperature, and light incidence were the microenvironmental variables that triggered the replacement (i.e., one species by another). Those variables also had effect on tree species-specific: Mexican beech (Fagus mexicana), Quebracho (Quercus delgadoana), Pezma (Cyathea fulva), Aguacatillo (Beilschmiedia mexicana), Pezma (Dicksonia sellowiana var. arachneosa), and Mountain magnolia (Magnolia schiedeana). Discussion. Our results confirm our hypothesis related to β-diversity but not with α-diversity; however, the tree community structure of the diversity was similar among transects. Our study represents the first effort to evaluate and link the soil microenvironmental effect on tree α and β-diversity, finding a high replacement in a small-fragment of Neotropical montane oak forest from eastern Mexico.
... Diatoms are capable of growing much faster than terrestrial plants [2], which in turn makes them a potential environment threat in case of massive algal blooms [3]. On the other hand, they may offer future solutions for the food and energy crisis [2,[4][5][6]. The broad scientific interest in diatoms is also due to their unique physiology: diatom cell walls (so-called valves, further denoted as diatom biosilica) exhibit fascinating morphological diversity. ...
Diatoms are unicellular algae and occur ubiquitously in almost every marine and freshwater habitat on earth. They produce intricately structured cell walls, which mainly consist of amorphous silica. To synthesize their cell walls, diatoms take up monosilicic acid from the environment and store it. These silicon storage pools (SSPs) can exceed the solubility of silicic acid by one to two orders of magnitude, as observed in various diatom species. However, their chemical composition and cellular localization has not yet been elucidated. It is suggested that SSPs may consist of stabilized aggregates such as pre-condensed silica particles or silica-containing vesicles. Isolation protocols for SSPs without significant chemical modification are required to prove such hypotheses. A critical issue is the efficient separation of components of the SSPs from cell wall fragments or artefacts, which may interfere with analytical methods targeting silicon. To this end, a comparative study was performed on exponentially grown cells and extracted, purified cell walls (biosilica) to observe the sedimentation behavior after lysis. Cell cultures were lysed by bead beating and then fractionated by differential centrifugation. The obtained fractions were analyzed for total silicon content (tSi) using molybdenum blue assay (MBA) after alkaline treatment. It was revealed that cell wall fragments are almost absent in fractions above 1000 × g. Compared with biosilica, a significantly higher silicon concentration is found in lysed cell pellets after centrifugation at moderately high forces. The differences correspond to a few percent of total cellular silicon, which are assumed to be part of SSPs. Only relatively low amounts of silica/silicic acid remain in the supernatant at high centrifugal forces. This indicates that SSPs are mainly present in larger aggregates that sediment at lower centrifugal forces. According to Stokes’ law, only silica particles below ca. 25 nm radius would remain in the final supernatant. This leads to the conclusion that SSPs must mainly consist of larger silica particles and/or are associated with larger compartments/aggregates.
... Carbon dioxide (CO 2 ) emissions from fossil fuels and industrial activity account for 65% of entire GHG emissions, conferring to the US Environmental Protection Agency (EPA, 2020). Energy is recognized as an important factor in sustainable development; therefore, limiting the use of fossil fuels and transitioning to renewable sources is one of the major reduction measures (Levitan et al., 2014;Dincer, 2000). Furthermore, due to the scarcity of fossil fuels and their high cost, the transition to renewable energy sources is even more necessary to ensure energy security and meet demand (Ellabban et al., 2014). ...
Purpose
Electricity plays an essential role in nations' economic development. However, coal and renewables currently play an important part in electricity production in major world economies. The current study aims to forecast the electricity production from coal and renewables in the USA, China and Japan.
Design/methodology/approach
Two intelligent grey forecasting models – optimized discrete grey forecasting model DGM (1,1,α), and optimized even grey forecasting model EGM (1,1, α , θ ) – are used to forecast electricity production. Also, the accuracy of the forecasts is measured through the mean absolute percentage error (MAPE).
Findings
Coal-powered electricity production is decreasing, while renewable energy production is increasing in the major economies (MEs). China's coal-fired electricity production continues to grow. The forecasts generated by the two grey models are more accurate than that by the classical models EGM (1,1) and DGM (1,1) and the exponential triple smoothing (ETS).
Originality/value
The study confirms the reliability and validity of grey forecasting models to predict electricity production in the MEs.
... Diatoms are among the ecologically most significant groups of microorganisms on the Earth, contributing 15-20% to the total primary photosynthetic productivity on the planet (Nelson et al. 1995, Armbrust 2009). Besides its primary ecological relevance, this phytoplankton group also promises a multitude of potential biotechnological applications, and the generation of diatom strains that are more suitable for growth in photobioreactors is of great interest (Bozarth et al. 2009, Levitan et al. 2014, Butler et al. 2020. One approach to improve photosynthetic productivity in a mass culture is to reduce its optical density to favor a more homogeneous light utilization and avoid light dissipation as thermal energy (Melis 2009, Vecchi et al. 2020. ...
CpFTSY is a component of the chloroplast signal recognition particle (CpSRP) pathway that post-translationally targets light-harvesting complex proteins (LHCPs) to the thylakoid membranes in plants and green algae containing chloroplasts derived from primary endosymbiosis. In plants, CpFTSY also plays a major role in co-translational incorporation of chloroplast encoded subunits of photosynthetic complexes to the thylakoids. This role has not been demonstrated in green algae. So far, its function in organisms with chloroplasts derived from secondary endosymbiotic events has not been elucidated. Here, we report the generation and characterization of mutants lacking CpFTSY in the diatom Phaeodactylum tricornutum. We found that this protein is not involved in inserting LHCPs into thylakoid membranes, indicating that the post-translational part of the CpSRP pathway is not active in this group of microalgae. Lack of CpFTSY caused an increased level of photoprotection, low electron transport rates, inefficient repair of PSII, reduced growth, a strong decline in the PSI subunit PsaC and upregulation of proteins that might compensate for a non-functional co-translational CpSRP pathway during light stress conditions. The phenotype was highly similar to the one described for diatoms lacking another component of the co-translational CpSRP pathway, the CpSRP54 protein. However, in contrast to cpsrp54 mutants, only one thylakoid membrane protein, PetD of the Cytb6f complex, was downregulated in cpftsy. Our results point to a minor role for CpFTSY in the co-translational CpSRP pathway, suggesting that other mechanism may partially compensate for the effect of a disrupted CpSRP pathway.
... In the present study, however, the focus is on the sulfolipid composition of model green algae, cyanobacteria and the lipidomics of Achnanthidium minutissimum, a diatom isolated from epilithic biofilms of Lake Constance (Dow et al. 2020;Windler et al. 2015;Windler 2014). Lipids make up about 25 to 45% of the total dry weight of diatoms (Levitan et al. 2014) and contain a variety of polar lipids (Popendorf, Fredricks, and Van Mooy 2013), and among them are the sulfolipids (SQDGs, sulfoquinovosyldiacylglycerols (Liebisch et al. 2020)) of special interest. ...
... Major components of diatoms are lipids, accounting for up to 25% of their dry weight (Levitan et al., 2014). Production of lipids in diatom varies depending on culture conditions (Yi et al., 2017), however, diatom lipid material contains nearly all lipid classes, including both polar (Guschina and Harwood, 2006) and neutral lipids, such as free fatty acids (FFA), sterols (ST) and triacylglycerols (TG). ...
Full text available at https://authors.elsevier.com/a/1gEs9AOM9ziJa
until January 31st, 2023! The global importance of abiotic oceanic production of volatile organic compounds (VOCs) still presents a source of high uncertainties related to secondary organic aerosol (SOA) formation. A better understanding of the photochemistry occurring at the ocean-atmosphere interface is particularly important in that regard, as it covers >70% of the Earth's surface. In this work, we focused on the photochemical VOCs production at the air-water interface containing organic material from authentic culture of marine diatom Chaetoceros pseudocurvisetus. Abiotic VOCs production upon irradiation of material originating from total phytoplankton culture as well as the fraction containing only dissolved material was monitored by means of PTR-ToF-MS. Furthermore, isolated dissolved lipid fraction was investigated after its deposition at the air-water interface. All samples acted as a source of VOCs, producing saturated oxygenated compounds such as aldehydes and ketones, as well as unsaturated and functionalized compounds. Additionally, a significant increase in surfactant activity following irradiation experiments observed for all samples implied biogenic material photo-transformation at the air-water interface. The highest VOCs flux normalized per gram of carbon originated from lipid material, and the produced VOCs were introduced into an atmospheric simulation chamber, where particle formation was observed after its gas-phase ozonolysis. This work clearly demonstrates abiotic production of VOCs from phytoplankton derived organic material upon irradiation, facilitated by its presence at the air/water interface, with significant potential of affecting the global climate as a precursor of particle formation.
... Brazil, Germany, France, Sweden, and the United States are leading countries in the consumption and development of biofuels (Adenle et al. 2013). It is observed that genetically modified algae shown significant enhancement in biomass, lipid accumulation, and carbon capturing capacity (Beacham et al. 2017;Shuba and Kifle 2018;Dutta et al. 2014;Levitan et al. 2014). Algal species are found in many shapes and sizes, extending from single-cell microalgae to multicellular filaments macroalgae in different aquatic habitats (Shafik et al. 2015). ...
Algae are aquatic species that may reproduce quickly and have over 3000 different breeds, making them more abrasive than terrestrial plants. They may be able to convert CO2 from the air into oxygen and remove it from the breaking cells of algae plants, which is how they produce wonderful oil. A viable source of feedstock for biofuels, oleaginous microalgae have a number of advantages over terrestrial plants. Due to the lack of robust algal strains with increased lipid content and biomass and methodologies for economically viable oil extraction, the microalgal fuel business is still in its infancy. By carefully targeting important metabolic nodes, microalgal metabolic engineering demonstrates the huge potential to improve lipid accumulation without compromising cell growth. The genetic enhancement of microalgae without impairing cellular biomass remains an underutilized option for large-scale biofuel production, despite recent advances in synthetic biology. To improve microalgae as a biofuel platform for the production of biohydrogen, alcohols generated from starch, substitutes for diesel fuel, and/or alkanes, we consequently present a thorough overview of numerous biotechnological techniques in this chapter.KeywordsBiofuelGenetic engineeringMicroalgaeNano-additiveBio-bricksBiorefinery
... Brazil, Germany, France, Sweden, and the United States are leading countries in the consumption and development of biofuels (Adenle et al. 2013). It is observed that genetically modified algae shown significant enhancement in biomass, lipid accumulation, and carbon capturing capacity (Beacham et al. 2017;Shuba and Kifle 2018;Dutta et al. 2014;Levitan et al. 2014). Algal species are found in many shapes and sizes, extending from single-cell microalgae to multicellular filaments macroalgae in different aquatic habitats (Shafik et al. 2015). ...
The need for alternative sources of renewable fuel was felt in 1970–1980 with research being directed toward exploring algae as the starter material for biofuel production. Algal varieties are enormous and its potential for biofuel production is immense and much higher than any land plant-based product. However, there are limitations in terms of making them commercially viable. Extensive research has been conducted to address each step to make the application economically viable, such as the energy requirement mainly in the harvesting step, water requirement for cultivation during the time of fresh water scarcity, and algal growth medium requirement for cultivation. This chapter reports a case study of selective treatment of ammonia-rich dairy wastewater using a consortium of bacteria and microalgae, revealing the potential of the technology in dairy wastewater treatment with lipid-rich algal biomass production for biofuel extraction. Such approach cuts down on the use of fresh water and algal growth medium for algae cultivation and saves energy by alleviating the need for harvesting the biofilm-based algal biomass. The reclaimed water could be reused for secondary (non-potable) applications. In this way the waste could be substituted for feed and water for algal growth, while biofilm-based growth ensured energy savings and a rapid treatment within 48 h ensured more efficient treatment and biomass production compared to conventionally reported algal consortium.
... Diatoms use stored carbon usually as chrysolaminarin or lipids (Kroth et al., 2008) and under nitrogen starvation, they reprogram the storage carbon from nitrogenous compounds like proteins and nucleic acid to neutral lipids (Valenzuela et al., 2012). It was recorded in a model marine diatom that under nitrogen stress, the cell allocated more nitrogen towards nitrogen assimilation enzymes compared to the photosynthetic apparatus, and the freshly produced carbon is utilized to synthesize more lipids (Levitan et al., 2014). Consequently, POC would increase at the cost of PON leading to a higher POC : PON ratio and is in agreement with our observation, particularly after D 6 ( Figure 2H). ...
Arctic phytoplankton are experiencing multifaceted stresses due to climate warming, ocean acidification, retreating sea ice, and associated changes in light availability, and that may have large ecological consequences. Multiple stressor studies on Arctic phytoplankton, particularly on the bloom-forming species, may help understand their fitness in response to future climate change, however, such studies are scarce. In the present study, a laboratory experiment was conducted on the bloom-forming Arctic diatom Chaetoceros gelidus (earlier C. socialis) under variable CO2 (240 and 900 µatm) and light (50 and 100 µmol photons m⁻² s⁻¹) levels. The growth response was documented using the pre-acclimatized culture at 2°C in a closed batch system over 12 days until the dissolved inorganic nitrogen was depleted. Particulate organic carbon and nitrogen (POC and PON), pigments, cell density, and the maximum quantum yield of photosystem II (Fv/Fm) were measured on day 4 (D4), 6 (D6), 10 (D10), and 12 (D12). The overall growth response suggested that C. gelidus maintained a steady-state carboxylation rate with subsequent conversion to macromolecules as reflected in the per-cell POC contents under variable CO2 and light levels. A substantial amount of POC buildup at the low CO2 level (comparable to the high CO2 treatment) indicated the possibility of existing carbon dioxide concentration mechanisms (CCMs) that needs further investigation. Pigment signatures revealed a high level of adaptability to variable irradiance in this species without any major CO2 effect. PON contents per cell increased initially but decreased irrespective of CO2 levels when nitrogen was limited (D6 onward) possibly to recycle intracellular nitrogen resources resulting in enhanced C: N ratios. On D12 the decreased dissolved organic nitrogen levels could be attributed to consumption under nitrogen starvation. Such physiological plasticity could make C. gelidus “ecologically resilient” in the future Arctic.
... diatom, nitrogen starvation, Phaeodactylum, proteome remodeling, quantitative proteomics Diatoms are one of the largest groups of phytoplankton biodiversity, dominating oceanic and freshwater ecosystems [1]. They have attracted attention as a promising resource for multiple biotechnological applications [2][3][4][5]. In spite of their ecological importance and economic potential, efforts are still needed to advance knowledge on their unique metabolism and powerful acclimation to their changing environment. ...
Diatoms are one of the largest groups in phytoplankton biodiversity. Understanding their response to nitrogen variations, present from micromolar to near‐zero levels in oceans and fresh waters, is essential to comprehend their ecological success. Nitrogen starvation is used in biotechnological processes, to trigger the remodeling of carbon metabolism in the direction of fatty acids and triacylglycerol synthesis. We evaluated whole proteome changes in Phaeodactylum tricornutum after 7 days of cultivation with 5.5‐mM nitrate (+N) or without any nitrogen source (−N). On a total of 3768 proteins detected in biological replicates, our analysis pointed to 384 differentially abundant proteins (DAP). Analysis of proteins of lower abundance in −N revealed an arrest of amino acid and protein syntheses, a remodeling of nitrogen metabolism, and a decrease of the proteasome abundance suggesting a decline in unselective whole‐proteome decay. Analysis of proteins of higher abundance revealed the setting up of a general nitrogen scavenging system dependent on deaminases. The increase of a plastid palmitoyl‐ACP desaturase appeared as a hallmark of carbon metabolism rewiring in the direction of fatty acid and triacylglycerol synthesis. This dataset is also valuable to select gene candidates for improved biotechnological properties.
... Our results showed that most fatty acids are stored and accumulated in P. tricornutum under long-term severe light fluctuations (Figure 4). Diatoms are rich in lipids (Chisti, 2007;Levitan et al., 2014;Wu et al., 2014). It has been shown that high light induced increases in fatty acids, while low light induced an increased proportion of unsaturated fatty acids (Orcutt and Patterson, 1974). ...
Unlike in terrestrial and freshwater ecosystems, light fields in oceans fluctuate due to both horizontal current and vertical mixing. Diatoms thrive and dominate the phytoplankton community in these fluctuating light fields. However, the molecular mechanisms that regulate diatom acclimation and adaptation to light fluctuations are poorly understood. Here, we performed transcriptome sequencing, metabolome profiling, and 13C-tracer labeling on the model diatom Phaeodactylum tricornutum. The diatom acclimated to constant light conditions was transferred to six different light conditions, including constant light (CL5d), short-term (1 h) high light (sHL1h), and short-term (1 h) and long-term (5 d) mild or severe light fluctuation conditions (mFL1h, sFL1h, mFL5d, sFL5d) that mimicked land and ocean light levels. We identified 2673 transcripts (25% of the total expressed genes) expressed differentially under different fluctuating light regimes. We also identified 497 transcription factors, 228 not reported previously, which exhibited higher expression under light fluctuations, including 7 with a light-sensitive PAS domain and 10 predicted to regulate genes related to light harvesting complex (LHC) proteins. Our data showed that prolonged pre-conditioning in severe light fluctuation enhanced photosynthesis in P. tricornutum under this condition, as evidenced by increased oxygen evolution accompanied by the upregulation of Rubisco and light harvesting proteins. Furthermore, severe light fluctuation diverted the metabolic flux of assimilated carbon preferentially towards fatty acid storage over sugar and protein. Our results suggest that P. tricornutum use a series of complex and different responsive schemes in photosynthesis and carbon metabolism to optimize their growth under mild and severe light fluctuations. These insights underscore the importance of using more intense conditions when investigating the resilience of phytoplankton to light fluctuations.
... Diatoms are ubiquitous photosynthetic microalgae found in aquatic environments that contribute about 40% of the phytoplankton primary production in the ocean and about 20% to global primary production (Falkowski et al. 2000;Armbrust 2009). Beyond this essential role in the environment, some species are used in a biotechnological context for their metabolic capacities as lipid producers, for instance (Mekhalfi et al. 2012;Levitan et al. 2014;Prioretti et al. 2017). There is no doubt that the presence of CCMs is one of the characteristics that allows diatoms to thrive in many environments since their Rubisco has an affinity constant for CO 2 between 23 and 68 µM (Young et al. 2016) that is too high to be saturated under air-equilibrium concentrations of CO 2 in both marine and freshwater environments. ...
... Table 1 summarizes the potential of the products extracted from microalgal biomass. To this end, a large body of literature shows the high potential of microalgal biore nery to extract biogas, liquid and gaseous transportation fuel, kerosene, ethanol, aviation fuel, biohydrogen, biodiesel, bioethanol, and bio-oil (Gallagher 2011, Sharma et al. 2011, Levitan et al. 2014. Others have investigated various microalgae-produced gases such as biogas, biohydrogen, and syngas (Demirbas 2010, Nigam & Singh 2011. ...
This review examines global microalgae, seaweeds, and duckweed (MSD) production status and trends. It focuses on cultivation, recognizing the sector's existing and potential contributions and benefits, highlighting a variety of constraints and barriers over the sector's sustainable development. It also discusses lessons learned and ways forward to unlock the sector's full potential. In contrast to conventional agriculture crops, MSD can rapidly generate large amounts of biomass and carbon sequestration yet does not compete for arable land and potable water, ensuring minimal environmental impacts. Moreover, MSD's applications are ubiquitous and reach almost every industrial sector, including ones essential to meeting the increasing needs of human society, such as foods, pharmaceuticals, and chemicals. To this end, the growing public awareness regarding climate change, sustainable food, and animal welfare yields a significant shift in consumer preference and propels the demand for MSD. In addition, once governments usher in durable and stable carbon policies, the markets for MSD are likely to increase severalfold.
Expected final online publication date for the Annual Review of Resource Economics, Volume 14 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Organic carbon may be obtained sustainably from lignocellulosic biomass; however, the majority of microorganisms, including microalgae, find it difficult to convert it through bioconversion due to its refractory nature. As a result, a significant challenge lies in the bioprospecting and metabolic engineering of microalgae to use lignocellulosic carbohydrates including cellulose, hemicellulose, and lignin with minimal pretreatment. Diatoms that are heterotrophic epiphytic are capable of consuming organic matter as they can naturally produce cellulolytic and hydrolytic enzymes, allowing them to effectively use lignocellulose for growth. They have a unique carbon metabolism which, due to the presence of enzymes, is exclusively involved in the breakdown of lignin via the β-ketoadipate pathway. This chapter focuses on how diatoms convert lignocellulose to produce biofuels and other value-added products that can help to achieve a sustainable environment in the near future.
Diatoms constitute a prominent group of phytoplankton characterized by their siliceous cell wall. They account for 20–25% of oxygen release and carbon dioxide fixation in the world. Diatoms yield bioactive compounds, one of which is lipids, and store fatty acids to produce different valuable products like omega-3 fatty acids, such as EPA and DHA, which are polyunsaturated fatty acids (PUFAs). Omega-3 fatty acids (EPA and DHA) have many health and medical benefits, including prevention and treatment of various diseases, and therefore taken on a regular basis. Due to this, there is an increased consumption of omega-3 fatty acids. Many studies found EPA and DHA content in various fatty fish which led to pressure on fish stock. An alternative source for producing omega-3 fatty acids is diatoms, the primary producer microalgae. This chapter discusses the importance of omega-3 fatty acids (EPA and DHA), lipid biosynthesis and factors influences lipid accumulation.
Green photosynthetic algae have gained much research interest due to their versatile nature of biomolecules’ production. They have unique features for the fixation of carbon dioxide (CO2) and bioremediation of wastewater. Microalgae biomass comprises a variety of biochemical components such as carbohydrates, lipids, proteins, and valuable pigments. The designing of its biorefinery can generate multiple feasible and sustainable feedstock to produce biofuels, pharmaceuticals, and food supplements. However, the cultivation of microalgae and its biorefinery is not technically feasible on a large scale, and that limits its commercialization. Moreover, the single product-based biorefinery increases the cost of the overall process. This book chapter discusses the classification and general overview of microalgae. Moreover, a brief overview of upstream and downstream processes such as cultivation, harvesting, drying, and extraction has been deliberated. Moreover, the applications of microalgae and its biomass in bioenergy, pharmaceuticals, and food production as well as environmental benefits also have been discussed. Furthermore, this book chapter focuses on the utilization of microalgae as an effective and economically feasible feedstock for biorefineries.
Electrocatalytic CO2 reduction (ECR) is one of the most promising way for CO2 mitigation and fuel production, where multicarbon products (C2+) with higher chemical value gain lots of interest. Cu...
Purpose – The importance of electricity in the economic development of nations is undeniable. Although coal and renewable sources are significant contributors to electricity production in major world economies, a new study seeks to predict the future production of electricity from these sources in Germany, the United Kingdom, and France.
Design/methodology/approach – Two optimized grey forecasting models – DGM (1,1,α) and EGM (1,1,θ,α) – are used to forecast electricity production. Also, the accuracy of the forecasts is measured through the Javed-Cudjoe scale of Mean Absolute Percentage Error (MAPE).
Findings – The electricity production from coal is on the decline, while renewable energy production is increasing in Germany, the United Kingdom, and France. The accuracy of the forecasts for these trends, as generated by two grey models, surpasses that of the Exponential Triple Smoothing (ETS).
Originality/value – For the first time, optimized even and discrete grey forecasting models have been utilized to make predictions about electricity production in the three largest economies in Europe.
Diatoms represent one of the most abundant groups of microalgae in the ocean and are responsible for approximately 20% of photosynthetically fixed CO2 on Earth. Due to their complex evolutionary history and ability to adapt to different environments, diatoms are endowed with striking molecular biodiversity and unique metabolic activities. Their high growth rate and the possibility to optimize their biomass make them very promising ‘biofactories’ for biotechnological applications. Among bioactive compounds, diatoms can produce ovothiols, histidine-derivatives, endowed with unique antioxidant and anti-inflammatory properties, and occurring in many marine invertebrates, bacteria and pathogenic protozoa. However, the functional role of ovothiols biosynthesis in organisms remains almost unexplored. In this work, we have characterized the thiol fraction of Phaeodactylum tricornutum, providing the first evidence of the presence of ovothiol B in pennate diatoms. We have used P. tricornutum to overexpress the 5-histidylcysteine sulfoxide synthase ovoA, the gene encoding the key enzyme involved in ovothiol biosynthesis and we have discovered that OvoA localizes in the mitochondria, a finding that uncovers new concepts in cellular redox biochemistry. We have also obtained engineered biolistic clones that can produce higher amount of ovothiol B compared to wild-type cells, suggesting a new strategy for the eco-sustainable production of these molecules.
Outdoor microalgal cultivation for the production of valuable biofuels and bioproducts typically requires high insolation and strains with high thermal (>37°C) tolerance. While some strains are naturally thermotolerant, other strains of interest require improved performance at elevated temperatures to enhance industrial viability. In this study, adaptive laboratory evolution (ALE) was performed for over 300 days using consecutive 0.5°C temperature increases in a constant temperature incubator to attain greater thermal tolerance in the industrially relevant diatom Nitzschia inconspicua str. Hildebrandi. The adapted strain was able to grow at a constant temperature of 37.5°C; whereas this constant temperature was lethal to the parental control, which had an upper‐temperature boundary of 35.5°C before adaptive evolution. Several high‐temperature clonal isolates were obtained from the evolved population following ALE, and increased temperature tolerance was observed in the clonal, parent, and non‐clonal adapted cultures. This ALE method demonstrates the development of enhanced industrial algal strains without the production of genetically modified organisms (GMOs).
In the current situation, almost every industrial and transportation activities are dependent on fossil fuels for their energy requirements. Fossil fuels are an overpriced and non-renewable source of energy. Besides these fossil fuels, combustion emits greenhouse gases that cause air pollution and global warming. Nowadays, microalgae-originated biofuels gained huge attention from researchers as they are expected to be a potential alternative to conventional fuels. Microalgal biofuel sector considers various strategies to enhance lipid content and biomass productivity in different habitats. To attain high lipid content from microalgae, lipid triggering circumstances are required to be optimized. This chapter summarizes various cultivation conditions, including pH, light intensity, and temperature for raised lipid accumulation inside microalgal cells. Different levels of physical factors affecting microalgal growth and lipid yield have been discussed in this chapter. The influence of the cultivation conditions such as CO2 concentration, temperature, light colour, and light intensity on lipid accumulation is evaluated comprehensively. Also, very recent progress and research studies on microalgal biomass and biodiesel production are discussed and summarized.
Minutocellus polymorphus MMDL5290, a minute diatom, can efficiently utilize organic nitrogen (N) urea as the sole N source and achieve equivalent growth rate and photosynthesis capacity as it does with nitrate. Interestingly, M. polymorphus MMDL5290 growing on urea-replete (400 μM) medium yields a similar growth rate to that on nitrate-replete (882 μM). So far, very few reports are available on the molecular regulation mechanisms of microalgae with similar growth potential under different N sources. To address this gap, our study aimed to characterize the differences in transcriptome-level responses of M. polymorphus MMDL5290 between nitrate-replete and urea-replete conditions. We identified 4075 differentially expressed genes between these two groups. Interestingly, gene expression in light-harvesting, electron transport chain, ATP synthesis, and chlorophyll and carotenoid synthesis was up-regulated under urea, while the expression of carbon fixation genes did not change significantly. Meanwhile, transcriptome profiling indicated that under the urea-replete condition, M. polymorphus MMDL5290 triggered massive gene expression reconfiguration, inducing cells to increase investment in protein synthesis and antioxidative stress. This may explain why higher photosynthetic capacity in urea-grown cells does not lead to higher growth. Furthermore, down-regulation of PT (signal peptide) genes was observed under the urea-replete condition, suggesting a repressed capacity of phosphate transport. In addition, we identified 139 stably and highly expressed genes, which have the potential to be used as candidate reference genes in future gene expression studies on M. polymorphus MMDL5290.
CRISPR/Cas enables targeted genome editing in many different plant and algal species including the model diatom Thalassiosira pseudonana. However, efficient gene targeting by homologous recombination (HR) to date is only reported for photosynthetic organisms in their haploid life‐cycle phase. Here, a CRISPR/Cas construct, assembled using Golden Gate cloning, enabled highly efficient HR in a diploid photosynthetic organism.
Homologous recombination was induced in T. pseudonana using sequence‐specific CRISPR/Cas, paired with a dsDNA donor matrix, generating substitution of the silacidin, nitrate reductase and urease genes by a resistance cassette (FCP:NAT).
Up to c. 85% of NAT‐resistant T. pseudonana colonies screened positive for HR by nested PCR. Precise integration of FCP:NAT at each locus was confirmed using an inverse PCR approach. The knockout of the nitrate reductase and urease genes impacted growth on nitrate and urea, respectively, while the knockout of the silacidin gene in T. pseudonana caused a significant increase in cell size, confirming the role of this gene for cell‐size regulation in centric diatoms.
Highly efficient gene targeting by HR makes T. pseudonana as genetically tractable as Nannochloropsis and Physcomitrella, hence rapidly advancing functional diatom biology, bionanotechnology and biotechnological applications targeted on harnessing the metabolic potential of diatoms.
Photosystem I (PSI) is a protein complex functioning in light-induced charge separation, electron transfer, and reduction reactions of ferredoxin in photosynthesis, which finally results in the reduction of NAD(P)− to NAD(P)H required for the fixation of carbon dioxide. In eukaryotic algae, PSI is associated with light-harvesting complex I (LHCI) subunits, forming a PSI-LHCI supercomplex. LHCI harvests and transfers light energy to the PSI core, where charge separation and electron transfer reactions occur. During the course of evolution, the number and sequences of protein subunits and the pigments they bind in LHCI change dramatically depending on the species of organisms, which is a result of adaptation of organisms to various light environments. In this chapter, I will describe the structure of various PSI-LHCI supercomplexes from different organisms solved so far either by X-ray crystallography or by cryo-electron microscopy, with emphasis on the differences in the number, structures, and association patterns of LHCI subunits associated with the PSI core found in different organisms.
The productivity of terrestrial plants can be limited by water supply and high temperature, but these factors are often replaced in aquatic plants by low light and restricted inorganic carbon supply. Furthermore, oxygen concentrations in water can be over two times greater than air‐equilibrium and low diffusion will restrict losses from the chloroplast to the environment. These conditions can cause underwater photosynthesis to be carbon‐limited, promoting photorespiration and favoring the possession of a CO 2 concentrating mechanism (CCM). Crassulacean acid metabolism (CAM) is similar to C 4 metabolism since the first product of carbon fixation in both pathways leads to the formation of C 4 organic acids. Future research could increase the number of aquatic species studied since only a fraction has been investigated for possessing a biochemical CCM. Detailed mechanistic studies, which are beginning to be carried out on marine diatoms, should be applied to a wider range of aquatic photoautotrophs.
Macronutrient availability and distribution across ocean provinces controls the distribution, abundance, and productivity of marine diatoms. Diatoms are a particularly successful group of phytoplankton thought to possess mechanisms that allow for rapid response and acclimation to shifting nutrient conditions while sustaining high rates of growth. Since the early 2000s, the availability of diatom genomes, functional genomics, and acceleration in development of genetic tools has led to the identification and characterization of adaptations diatoms possess that help explain their ecological dominance under certain conditions. The molecular basis of the ability of diatoms to outcompete other taxa for available nitrogen has been established and understanding the sensing, regulation, and other nuances of this response continues to be a major theme of ongoing research in the field. Further, major developments in the phosphorus uptake and sensing machinery of diatoms have emerged, enabled entirely by genome-enabled research. Additional knowledge of the acquisition machinery used for silicon uptake and metabolism of sulfur compounds has also resulted from analysis of diatom genomes. In this chapter, we review studies on macronutrient utilization in diatoms from the lab and in the field, highlight several notable insights that have emerged from this first era of diatom molecular research, and identify emerging paradigms that represent exciting areas for future study.
Microalgae are a diverse group of photosynthetic microorganisms with considerable potential as a source of bioenergy. Metabolic profiles, product yields, crop protection, and strain optimization influence production costs and therefore the feasibility of algal biofuels. Recent advances in microalgal genetic engineering offers the ability to generate transgenic strains with enhanced profiles for biofuel production. In this chapter we review the molecular tools and techniques developed for algae genetic engineering, including methods for genetic transformation and stable heterologous gene expression. Recent successes in algal genetic engineering to advance algal biofuels production are discussed, as well as potential ways to use molecular genetics for algal biotechnology in the future.
It is widely established that nutritional nitrogen deprivation increases lipid accumulation but severely decreases growth rate in microalgae. To understand the regulatory branch points that determine the partitioning of carbon among its potential sinks, we analyzed metabolite and transcript levels of central carbon metabolic pathways and determined the average fluxes and quantum requirements for the synthesis of protein, carbohydrates and fatty acid in the diatom Phaeodactylum tricornutum. Under nitrate-starved conditions, the carbon fluxes into all major sinks decrease sharply; the largest decrease was into proteins and smallest was into lipids. This reduction of carbon flux into lipids together with a significantly lower growth rate is responsible for lower overall FA productivities implying that nitrogen starvation is not a bioenergetically feasible strategy for increasing biodiesel production. The reduction in these fluxes was accompanied by an 18-fold increase in α-ketoglutarate (AKG), 3-fold increase in NADPH/NADP+, and sharp decreases in glutamate (GLU) and glutamine (GLN) levels. Additionally, the mRNA level of acetyl-CoA carboxylase and two type II diacylglycerol-acyltransferases were increased. Partial suppression of nitrate reductase by tungstate resulted in similar trends at lower levels as for nitrate starvation. These results reveal that the GS/GOGAT pathway is the main regulation site for nitrate dependent control of carbon partitioning between protein and lipid biosynthesis, while the AKG/GL(N/U) metabolite ratio is a transcriptional signal, possibly related to redox poise of intermediates in the photosynthetic electron transport system.
Significance
As global CO 2 levels rise and fossil fuel abundance decreases, the development of alternative fuels becomes increasingly imperative. Biologically derived fuels, and specifically those from microalgae, are promising sources, but improvements throughout the production process are required to reduce cost. Increasing lipid yields in microalgae without compromising growth has great potential to improve economic feasibility. We report that disrupting lipid catabolism is a practical approach to increase lipid yields in microalgae without affecting growth or biomass. We developed transgenic strains through targeted metabolic engineering that show increased lipid accumulation, biomass, and lipid yields. The target enzyme’s ubiquity suggests that this approach can be applied broadly to improve the economic feasibility of algal biofuels in other groups of microalgae.
In spite of attractive attributes, diatoms are underrepresented in research and literature related to the development of microalgal biofuels. Diatoms are highly diverse and have substantial evolutionarily-based differences in cellular organization and metabolic processes relative to chlorophytes. Diatoms have tremendous ecological success, with typically higher productivity than other algal classes, which may relate to cellular factors discussed in this review. Diatoms can accumulate lipid equivalently or to a greater extent than other algal classes, and can rapidly induce triacylglycerol under Si limitation, avoiding the detrimental effects on photosynthesis, gene expression and protein content associated with N limitation. Diatoms have been grown on production scales for aquaculture for decades, produce value-added products and are amenable to omic and genetic manipulation approaches. In this article, we highlight beneficial attributes and address potential concerns of diatoms as biofuels research and production organisms, and encourage a greater emphasis on their development in the biofuels arena.
We determined the quantum requirements for growth (1/phi) and fatty acid (FA) biosynthesis (1/phi FA) in the marine diatom, Phaeodactylum tricornutum, grown in nutrient replete conditions with nitrate or ammonium as nitrogen sources, and under nitrogen limitation, achieved by transferring cells into nitrogen free medium or by inhibiting nitrate assimilation with tungstate. A treatment in which tungstate was supplemented to cells grown with ammonium was also included. In nutrient replete conditions, cells grew exponentially and possessed virtually identical 1/phi of 4044mol photonsmol C1. In parallel, 1/phi FA varied between 380 and 409mol photonsmol C1 in the presence of nitrate, but declined to 348mol photonsmol C1 with ammonium and to 250mol photonsmol C1 with ammonium plus tungstate, indicating an increase in the efficiency of FA biosynthesis relative to cells grown on nitrate of 8% and 35%, respectively. While the molecular mechanism for this effect remains poorly understood, the results unambiguously reveal that cells grown on ammonium are able to direct more reductant to lipids. This analysis suggests that when cells are grown with a reduced nitrogen source, fatty acid biosynthesis can effectively become a sink for excess absorbed light, compensating for the absence of energetically demanding nitrate assimilation reactions. Our data further suggest that optimal lipid production efficiency is achieved when cells are in exponential growth, when nitrate assimilation is inhibited, and ammonium is the sole nitrogen source.
Background
Nitrogen limitation can induce neutral lipid accumulation in microalgae, as well as inhibiting their growth. Therefore, to obtain cultures with both high biomass and high lipid contents, and explore the lipid accumulation mechanisms, we implemented nitrogen deprivation in a model diatom Phaeodactylum tricornutum at late exponential phase.
Results
Neutral lipid contents per cell subsequently increased 2.4-fold, both the number and total volume of oil bodies increased markedly, and cell density rose slightly. Transcriptional profile analyzed by RNA-Seq showed that expression levels of 1213 genes (including key carbon fixation, TCA cycle, glycerolipid metabolism and nitrogen assimilation genes) increased, with a false discovery rate cut-off of 0.001, under N deprivation. However, most light harvesting complex genes were down-regulated, extensive degradation of chloroplast membranes was observed under an electron microscope, and photosynthetic efficiency declined. Further identification of lipid classes showed that levels of MGDG and DGDG, the main lipid components of chloroplast membranes, dramatically decreased and triacylglycerol (TAG) levels significantly rose, indicating that intracellular membrane remodeling substantially contributed to the neutral lipid accumulation.
Conclusions
Our findings shed light on the molecular mechanisms of neutral lipid accumulation and the key genes involved in lipid metabolism in diatoms. They also provide indications of possible strategies for improving microalgal biodiesel production.
Oyster greening was first described in the seventeenth century as a natural phenomenon. However, it has recently been discovered that the diatom Haslea ostrearia Simonsen causes greening by synthesis of a blue pigment designated as ‘marennine’. This phenomenon, which involves massive proliferation of H. ostrearia in oyster ponds, was not understood or controlled by oyster farmers in the Marennes-Oléron region (Atlantic coast of France). As greening oysters improved their market value, they tried to develop empirical methods to guarantee oyster fattening and improve profits. In this context, the present study investigated the feasibility of mass culture of diatoms outdoors in 10-m3 ponds, using enriched seawater. Different biotic and abiotic parameters were monitored daily to determine the influence of the day–night temperature range. After 8 days, H. ostrearia was the dominant diatom species (66%), reaching a mean cell concentration of 2 × 105 cell mL−1 and a marennine concentration of 3.4 mg L−1. Although intensive greening was obtained, further studies are required to optimize the production stages before this technology can be transferred to oyster farmers.
Here, we describe the first system for genetic transformation of Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, the only diatom for which a complete genome sequence is presently available. This method is based on microparticle bombardment followed by selection of transformants using the antibiotic nourseothricin. It exhibits the highest transformation efficiency compared with transformation systems for other diatom species. To achieve the high transformation efficiency, it is important to allow recovery of the bombarded T. pseudonana cells in non-selective suspension culture before spreading on nourseothricin containing agar plates. It is demonstrated that T. pseudonana is readily susceptible to co-transformation allowing for the simultaneous introduction of a non-selective gene together with the selection marker gene. Both introduced genes are stably inherited even in the absence of the antibiotic selection pressure. We have developed two T. pseudonana-specific expression vectors that can drive constitutive expression (vector pTpfcp) and inducible expression (vector pTpNR) of introduced genes. In combination with the available genome data the T. pseudonana transformation system is expected to provide a powerful tool for functional genomics in diatoms.
During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected
to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent
degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant
issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable
oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of
monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for
assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a
disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated
more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter
than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but
their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest
catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous
materials such as metals on oxidative stability.
Phaeodactylum tricornutum is a unicellular diatom in the class Bacillariophyceae. The full genome has been sequenced (<30 Mb), and approximately 20 to 30% triacylglyceride (TAG) accumulation on a dry cell basis has been reported under different growth conditions. To elucidate P. tricornutum gene expression profiles during nutrient-deprivation and lipid-accumulation, cell cultures were grown with a nitrate to phosphate ratio of 20:1 (N:P) and whole-genome transcripts were monitored over time via RNA-sequence determination.
The specific Nile Red (NR) fluorescence (NR fluorescence per cell) increased over time; however, the increase in NR fluorescence was initiated before external nitrate was completely exhausted. Exogenous phosphate was depleted before nitrate, and these results indicated that the depletion of exogenous phosphate might be an early trigger for lipid accumulation that is magnified upon nitrate depletion. As expected, many of the genes associated with nitrate and phosphate utilization were up-expressed. The diatom-specific cyclins cyc7 and cyc10 were down-expressed during the nutrient-deplete state, and cyclin B1 was up-expressed during lipid-accumulation after growth cessation. While many of the genes associated with the C3 pathway for photosynthetic carbon reduction were not significantly altered, genes involved in a putative C4 pathway for photosynthetic carbon assimilation were up-expressed as the cells depleted nitrate, phosphate, and exogenous dissolved inorganic carbon (DIC) levels. P. tricornutum has multiple, putative carbonic anhydrases, but only two were significantly up-expressed (2-fold and 4-fold) at the last time point when exogenous DIC levels had increased after the cessation of growth. Alternative pathways that could utilize HCO3- were also suggested by the gene expression profiles (e.g., putative propionyl-CoA and methylmalonyl-CoA decarboxylases).
The results indicate that P. tricornutum continued carbon dioxide reduction when population growth was arrested and different carbon-concentrating mechanisms were used dependent upon exogenous DIC levels. Based upon overall low gene expression levels for fatty acid synthesis, the results also suggest that the build-up of precursors to the acetyl-CoA carboxylases may play a more significant role in TAG synthesis rather than the actual enzyme levels of acetyl-CoA carboxylases per se. The presented insights into the types and timing of cellular responses to inorganic carbon will help maximize photoautotrophic carbon flow to lipid accumulation.
Two C26 sterane ratios, the 24-nordiacholestane ratio (NDR) and the 24-norcholestane ratio (NCR), are useful for assessing petroleum source age. Values for these parameters generally increase in the Cretaceous when diatoms were rapidly radiating and further in the Oligo-Miocene due to widespread high-latitude deposition of diatomaceous sediments. Sources with shale lithologies tend to exhibit the highest ratios; while carbonate and terrigenous-rich lithologies generally show lower ratios. On the North Slope of Alaska, elevated ratios are observed for Cretaceous HRZ oils and mixed oils containing Cretaceous input compared to older Triassic and Jurassic derived oils. Tertiary-sourced oils from Romania and Bulgaria have much higher ratios relative to Jurassic-sourced oils in the Black Sea region. Oleanane was observed in comparable levels in some Black Sea Tertiary and Jurassic oils and source rocks. NDR and NCR coupled with other age-diagnostic indicators (such as oleanane and dinosterane) provide powerful tools for differentiating age of source and organic facies for oils from the Black Sea and Sub-Andean Basins of Peru and Ecuador, respectively. Oils derived from sources deposited in low tropical latitudes tend to have little diatom input and as a consequence, do not display high values regardless of age.
With increasing concerns about the world's crude oil consumption, alternative fuels based on renewable resources attract more and more attention. Microalgae have been proposed to be one of the most sustainable feedstocks for the production of lipid-based biodiesel. Naturally occurring, high-lipid producing microalgae strains can be domesticated and further genetically improved in order to redirect metabolite fluxes towards increased lipid contents. This review summarizes the current knowledge about metabolic engineering of microalgae in order to increase the cellular lipid content, with an emphasis on triacylglycerols for the production of biofuels. Additionally, it outlines the contribution of systems biology and genome-scale metabolic pathway modeling, as well as their potential impact in the future.
This chapter provides a brief history of the conceptual framework of plankton evolutionary ecology to explain why the role of defense in the evolution of unicellular plankton has been neglected so far. The aim of this historical overview is also to point out what can be learned from studying the arms race: the other side of the coin. Given the range of attack techniques to which protists are exposed—from viruses to zooplankton—armor is defined as all forms of mechanical defense against pathogens, parasites, and ingestors. These in turn will range from slimy or tough cell walls that hamper purchase, bar entry, or withstand puncturing to long spines that deter ingestion. Following a brief comparison with terrestrial systems the chapter expands on the argument, that evolution of eukaryotes in the plankton is driven by the arms race. To this end, the range of attack systems evolved by pathogens, parasites, and predators in the plankton is surveyed, align them with their respective defense systems, and speculate on their evolutionary history. In the final section, the chapter examines how the various types of armor, that is, cell walls, scales, frustules, and colony skin of selected groups provide protection against specific forms of attack. In order to link structural features of an organism to a function, knowledge of the physical and ecological context, andthus,of the factors that cause significant selection pressure, is crucial.
The generally held view that fat accumulation is characteristic of certain classes of algae is based on inadequate evidence.
In this investigation the fatty acid, unsaponifiable lipoid, total cell nitrogen, and hydrolysable polysaccharide contents of the following algae have been determined at various stages during growth in pure culture: Chlorella vulgaris, Scotiella sp., Euglena gracilis var. bacillaris, Tribonema aequale, Monodus subterraneus, Navicula pelliculosa, Porphyridium cruentum, Anabaena cylindrica, and Oscillatoria sp.
Using the results obtained, the capacities of the algae to accumulate fat have been compared in the following ways: (I) on a percentage dry-weight basis; (2) by means of the differential growth factor relating the fat content of cultures to dry weight of algal material; (3) by consideration of the proportion which fats form of the total reserve material (taken as fat plus hydrolysable polysaccharide) as a function of total cell nitrogen content.
Species belonging to the same class have been found to resemble each other in the relative amounts of crude protein, fats, and hydrolysable polysaccharide which they contain. Marked differences in composition between species belonging to different classes have been found, but it is concluded that there are no funda mental differences in the physiological relations of fat accumulation in the algae belonging to the Chlorophycese, Euglenineae, Xanthophyceae, and Bacillario phyceae. Representatives of the Rhodophyceae and Myxophyceae, although they may under certain circumstances have moderately high fat contents, appear to differ in that in them fat accumulation is not associated with low cell nitrogen contents as it is in the other algae examined.
No well-defined correlations between the unsaponifiable lipoid and either the fatty acid or total cell nitrogen contents of the algae have been found. Euglena gracilis var. bacillaris has been found to have a rather higher content of unsaponifiable lipoid than the other algae.
Measurement studies of online social networks show that all social links are not equal, and the strength of each link is best characterized by the frequency of interactions between the linked users.To date, few studies have been able to examine detailed interaction data over time, and none have studied the problem of modeling user interactions. This paper proposes a generative model of social interactions that captures the inherently heterogeneous strengths of social links, thus having broad implications on the design of social network algorithms such as friend recommendation, information diffusion and viral marketing.
Wall formation in Navicula pelliculosa was studied in Si-starvation synchrony. Electron microscopy of walls, prepared by mechanical shaking, indicated that they were free, of cytoplasmic contamination. Removal of the frustule, using HF, indicated that a higher ratio of organic material to silica occurred in the girdle bands below the punctae and in the raphe region. The organic material was investigated following incorporation of (14)C. Material added to newly formed walls prior to and during Si-deposition contained more radioactivity in amino acids than in other constituents. Once Si-uptake ceased, material with increased fucose and xylose content became labelled. Secondary material, the main labelled constituents of which were mannose and glucoronic acid, was added to old walls at all times. Si-uptake was investigated using (31)Si. The rate of assimilation increased during the first hour following addition, remained constant over the next three hours, and then decreased markedly during the separation of daughter cells. Varying amounts of (31)Si could be extracted from intact cells, using hot or cold solvents. These results are discussed in relation to the sequence in which proteinaceous material and polysaccharides are formed during morphogenesis of the diatom wall.
The improvement of water quality in Lake Tega, Japan, has been carried out by dilution, causing the shift of dominant species from Microcystis aeruginosa to Cyclotella sp. in summer. The disappearance of Microcystis blooms would be related to dilution, but the detail effect has not been understood yet. In this study, the effect of nitrate concentration on the competition between M. aeruginosa and Cyclotella sp. was investigated through the single-species and the competitive culture experiments. The single-species culture experiment indicated that the half saturation constants for M. aeruginosa and Cyclotella sp. were 0.016 and 0.234 mg N L−1, representing that M. aeruginosa would possess a higher affinity to nitrate. On the other hand, the maximum growth rate for Cyclotella sp. was obtained as 0.418 day−1, which did not represent a significant difference with 0.366 day−1 obtained for M. aeruginosa. The competitive culture experiment revealed that Cyclotella sp. completely dominated over M. aeruginosa at the nitrate concentrations of 0.5 and 2.5 mg N L−1. The dominance of Cyclotella sp. could be attributed to the difference in the abilities of nitrate storage as well as nitrate uptake. One of the possibilities for the disappearance of Microcystis blooms caused by dilution as observed in Lake Tega could be due to the decrease in nitrate concentration, and the lower N:P ratio seemed not to relate to Microcystis blooms.
The major accomplishment of the past nine months' work was the identification of a microalgal species which can be grown in the system on a 12-month basis without temperature control. The most promising species identified to date is a strain of platymonas sp. This strain grows rapidly at temperatures from 20° to 34°C, and at salinities from 1.5 to 3.5%. Neither the lower temperature limit nor the lower salinity limit of the strain are known at this time. A factorial experiment designed to determine optimum growth conditions indicated that the optimum culture depth was 10 cm, the optimum pH about 7.5, and the optimum flow rate about 30 cm/s. A major discovery was that diluting the culture every third day greatly enhanced production. In this dilution mode daily yields averaged 46 g/m² ash-free dry weight (AFDW) over a one-month period, and photosynthetic efficiencies averaged 11% (based on visible light energy). The former figure is over twice the best long-term yields achieved in microalgal mass culture systems grown exclusively on inorganic nutrients.
Biomarkers, molecular fossils, are organic compounds in Holocene to Precambrian sedimentary deposits that can be related to specific chemical compounds produced in the biosphere. We demonstrate here that 24-norcholestane biomarkers, i.e., C26 steranes (saturated hydrocarbons having a steroid skeleton), can be useful to constrain the age and paleolatitude of geologic samples. The biological precursors of 24-norcholestanes remain unclear, but samples from more than 100 basins provide evidence that 24-norcholestanes may be derived directly or indirectly from diatoms. Ratios of 24-norcholestanes to 27-norcholestanes show an initial increase above background in Jurassic oils, but they increase dramatically in Cretaceous oils, coincident with diatom evolution. The highest ratios are found in oils and rock extracts from Oligocene or younger marine siliceous source rocks in which the sources were deposited at paleolatitudes >30°N.
Total fatty acid, total sterol, fatty acids of specific lipid classes, and unsaturated fatty acids produced inNitzschia closterium were compared qualitatively and quantitatively as a function of changes in light intensity. Increased levels of total fatty
acids were observed in cells grown at high light intensity when compared to cells grown at low light intensity. However, the
percentage of unsaturated fatty acid decreased under high light conditions. Fatty acid analysis of triglyceride and 1,3 diglyceride
fractions indicated an increase in levels of fatty acid at high light intensity when compared to low light intensity, while
levels of polar lipid fatty acids increased at low light intensity. These analyses can be taken to indicate an increase in
triglyceride and diglyceride at high light and a decrease in polar lipid at high light. Levels of free fatty acids did not
differ significantly with light intensity. The levels of total sterol also were unaffected by changes in light intensity.
However, levels of sterol isolated as free sterol and sterol associated in a yet unknown manner in the polar lipid fraction
varied with changes in light intensity. Levels of polar lipid sterol increased at high light intensity compared to low light
intensity, while the opposite was true for free sterol. The greatest percentage of total sterol was found in the polar lipid
class regardless of light intensity.
The economics of liquid-fuels production from microalgae was evaluated. A detailed review of published economic analyses of microalgae biomass production revealed wide variations in the published costs, which ranged from several dollars per pound for existing commercial health-food production in the Far East, to less than .05/lb costs projected for microalgae biomass for fuel conversion. As little design information or specific cost data has been published, a credible cost estimate required the conceptual engineering design and cost estimating of microalgae to liquid-fuels processes. Two systems were analyzed, shallow (2 to 3'') covered ponds and deeper (1 ft) open ponds. Only the latter was selected for an in-depth analysis due to the many technical shortcomings of the former approach. Based on the cost analysis of a very simple and low cost process, the most optimistic costs extrapolated were about $60/barrel. These were based on many optimistic assumptions. Additional, more detailed, engieering and cost analyses would be useful. However, the major emphasis in future work in this area should be on demonstrating the basic premises on which this design was based: high productivity and oil content of microalgae strains that can dominate in open ponds and which can be harvested by a simple bioflocculation process. Several specific basic research needs were identified: (1) Fundamentals of species selection and control in open pond systems. Effects of environmental variables on species dominance is of particular interest. (2) Mechanisms of algae bioflocculation. (3) Photosynthetic pathways and efficiency under conditions of high lipid production. (4) Effects of non-steady state operating conditions, particularly pH (COâ availability), on productivity. 18 figures, 47 tables.
The lipids and fatty acids of two freshwater diatoms Nitzschia palea Kutz, Navicula muralis Lewin, and one marine species, Navicula incerta Grun. have been studied.
The major lipid components in all species were triglycerides, monogalactosyl, digalactosyl and sulphoquinovosyl diglycerides,
phosphatidyl glycerol, phosphatidyl choline (lecithin), and phosphatidyl ethanolamine; while palmitoleic, palmitic, eicosapentaenoic
and eicosate-traenoic acids were the major fatty acid constituents. The two galactolipids, monogalactosyl and digalactosyl
diglycerides contained large amounts of C16 and C20 polyunsaturated fatty acids.
Lipids of diatoms, whether grown in the light or in the dark, were the same apart from quantitative differences. More storage
lipids such as triglycerides were synthesized in the light than in the dark.
Characteristics of the growth of Phaeodactylum in culture in fertilized sea water in 1,000‐L concrete tanks are described. Successful experiments showed a constant pattern of events as follows: 1) active growth of Phaeodactylum, 2) reduction in growth rate of Phaeodactylum, 3) period of constant cell density, or rapid decline, 4) regeneration period, and, 5) second period of active growth.
Growth of Phaeodactylum shows seasonal variation, but final population density reached is more or less constant. N and P utilization follow parallel courses, the mean ratio of N:P uptake during the 1st growth period being 6.5 ± 0.44:1. During growth, inorganic P is incorporated in the cells as particulate organic P. Following decline of Phaeodactylum dissolved organic P increases, and later, inorganic P is regenerated and may be reutilized during the 2nd growth phase. Decline of Phaeodactylum is normally associated with increase of the heterotroph Monas. There was a close relationship between peak numbers of Monas and the number of Phaeodactylum in the previous peak. The second growth phase consisted either of one or more chlorophycean flagellates, or of Phaeodactylum.
Estimates of production based on O 2 bottle exposures, change in inorganic P, change in pH, and change in packed cell volume agree closely, although initial uptake of P may be excessive. Estimates from change in inorganic P indicate a seasonal variation in the rate of organic production of up to 2.2 gC/m ² /24 hr in March, 4.9 gC/m ² /24 hr in May–August, and 2.0 gC/m ² /24 hr in October, November. For Tetraselmis production rates up to 5.2 gC/m ² /24 hr were recorded.
The efficiency of utilization of solar energy for Phaeodactylum culture ranged from 3.0 to 4.4% with a mean for 5 estimates of 3.7%. For Tetraselmis values of 1.0–1.3% were obtained.
The designs and systems developed include many innovative concepts and experiments, including the design and operation of a low-cost system. Cost-effectiveness is realized by minimizing capital costs of the system and achieving efficient use of inputs. Extensive engineering analysis of carbonation, mixing, and harvesting subsystems has elucidated both the lowest cost, most efficient options and the essential parameters needed to construct, test, and evaluate these subsystems. The use of growth ponds sealed with clay and lined with crushed rock results in construction cost savings of 50% over ponds lined with synthetic membranes. In addition a low-cost but efficient design allows improvements in technology to have maximum impact on final product cost reductions. In addition to the innovations in low-cost construction, the operational efficiency of the design is both higher and more feasible than that attained by any previous system concept of comparable scale. The water analysis has led to operational specifications that minimize water use and virtually eliminate losses of carbon dioxide to the atmosphere. The carbon dioxide injection system is designed for 95% efficiency, but is still low in cost. The construction of a large-scale, covered anaerobic lagoon to recycle carbon, nitrogen, and phosphorus has not been attempted at the scale analyzed here. Yet efficient recycling is essential for achieving economic affordability. 23 refs., 21 figs., 53 tabs.
TWENTY-FIVE years ago the large scale culturing of unicellular algae was
viewed with great enthusiasm as an alternative method for producing
protein1. This hope diminished by the late 1960s when it
seemed that the process was uneconomical because of a combination of
technical problems, most notably the recovery of the algal product and
its subsequent conversion to a human food and/or food supplement.
In the section entitled 'Photobioreactors for Mic roalgae Production of
Fuels and Chemicals' the authors consider the current and potential
commercial products that can be derived from microalgae during a process
of CO2 utilization, alternative photobioreactor designs, and the
fundamental biological and bioengineering issues in microalgae
production. They emphasize the long term potential of microalgae
production of low value commodities, specifically alternative fuels,
which would have the greatest potential for large-scale CO2 utilization.
Section 2 discusses the development of low cost technologies for macro
algae harvesting. First a brief review of the current experience in
algae harvesting in large-scale commercial operations is presented. This
is followed by a general discussion of various algae harvesting
processes, followed by a comparative evaluation of the various processes
and discussion of future prospects.
Molecular biological markers, or biomarkers, are natural products that can be assigned to a particular biosynthetic origin. For environmental and geological studies, the most useful molecular biomarkers are organic compounds with high taxonomic specificity and potential for preservation. This chapter introduces some of the general principles, provides examples of their use for discerning the identities and physiologies of microbes in contemporary environments and summarizes biomarker research aimed at elucidating aspects of biological and environmental evolution in the Precambrian.
In tropical and subtropical countries, hatcheries may produce microalgae for larval feeding either indoors, which is supposed to improve the quality and reliability of production but has a higher cost, or they may use outdoor cultures at a lower cost, but with a high seasonal variability. In this paper, we compare the cell concentrations and the organic biomass yields and composition of indoor and outdoor mass cultures of the diatom Chaetoceros muelleri obtained in four seasons in a commercial hatchery of the state of Sonora, in the Mexican northwest. Cell yields were better outdoors in spring and fall but lower in winter, whereas in summer they were similar indoors and outdoors. Organic biomass production was higher in spring and summer and tended to be lower, but not significantly different, in winter. Indoors, the percentage of proteins was significantly higher during spring, but it was lower in fall and winter. In summer, there was no difference between outdoors and indoors. Carbohydrates were higher indoors in summer, when lipids were higher outdoors, whereas in winter they were higher indoors. The organic biomass production ranged from 22.5 to 45.7g/m3/d indoors, with a mean estimated cost of US50.36 per kg.
As a result of algae's promise as a renewable energy feedstock, numerous studies have used Life Cycle Assessment (LCA) to quantify the environmental performance of algal biofuels, yet there is no consensus of results among them. Our work, motivated by the lack of comprehensive uncertainty analysis in previous studies, uses a Monte Carlo approach to estimate ranges of expected values of LCA metrics, such as Energy Return on (Energy) Invested (EROI), by incorporating parameter variability with empirically specified distribution functions. Results show that large uncertainties exist at virtually all steps of the biofuel production process. Although our findings agree with a number of earlier studies on matters such as the need for wet lipid extraction, nutrients recovered from waste streams, and high energy co-products, the ranges of reported values of LCA metrics help explain the high variability in EROI values from earlier studies. Reporting results from LCA models as ranges, and not single values, are necessary to reliably inform industry and policy makers on expected energetic and environmental performance of biofuels produced from microalgae.
Use of sedimentary organic carbon concentrations as a record of
paleoceanographic conditions is complicated by an insufficient
understanding of the mechanisms controlling present-day variations in
the organic matter content of surface open ocean sediments. This paper
is a review of organic carbon distributions in marine sediments, the
global marine balance of particulate and dissolved organic carbon and
the processes controlling organic matter diagenesis. The discussion
focuses on the last topic with the intention of bringing together mass
balance and organic chemical evidence for mechanisms that control the
preservation of organic matter in open ocean sediments.
Lipid synthesis of three marine diatoms was studied with a 14CO2 incorporation technique in silicate limited batch cultures. Growth rates were independent of the silicate concentration but the cellular yields were proportional to the initial amount of silicate. At the beginning of the stationary growth phase, lipid synthesis rates per unit culture volume increased by 1.7 times for Chaetoceros gracilis, 3.1 times for Hantzschia sp., and 2.8 times for Cyclotella sp., respectively compared to those during the exponential growth phase. Lipid carbon accounted for as much as 57% of the carbon in C. gracilis, 71% in Hantzschia sp., and 65% in Cyclotella sp., respectively. Additional enrichment with silicate during stationary growth phase allowed the cultures to grow further. Lipid synthesis rates were reduced during the subsequent growth phase, and the growth rates themselves were dependent on the level of biomass achieved during the previous stationary phase. However, the cellular yields were similar and probably controlled by light.
The lipid content of various phytoplankton species was measured in response to nitrogen and silicon limitation and over the cell cycle in synchronized cultures. In a survey of 30 species it was found that during log‐phase growth, green algae contained an average of 17.1% total lipids (% of total dry weight), whereas diatoms contained an average of 24.5%. Nitrogen deprivation for 4 to 9 days resulted in 2‐ to 3‐fold increases in the lipid content of green algae, whereas both increases and decreases were noted in diatoms, depending on the species. The greatest lipid content measured in the study was 72% in Monallantus salina (strain GSB Sticho) which had been deprived of nitrogen for 9 days. Nitrate replenishment in a nitrogen starved culture of Oocystis polymorpha Groover & Bold showed that the excess cellular lipids do not rapidly disappear during recovery, until cell division occurs.
A silicate deprivation experiment with Cyclotella cryptica Reimann, Lewin & Guillard (strain 7c) showed an increase in the total cellular lipid fraction from. 30 to 42% of dry weight within 6 h of the onset of silicon limitation, while the mass of lipid material per cell doubled within 12 h. The total lipid fraction in O. polymorpha was found to remain constant over the cell cycle in synchronized cultures regardless of the light regime. The data presented provided the first internally consistent study of phytoplankton lipids for a wide range of species and several growth conditions.
Biodiesel, defined as monoalkyl fatty acid ester (preferentially methyl and ethyl esters), represents a promising alternative fuel for use in compression-ignition (diesel) engines. Biodiesel fuel comes from renewable sources as it is plant- not petroleum-derived and as such it is biodegradable and less toxic. In addition, relative to conventional diesel, its combustion products have reduced levels of particulates, carbon oxides, sulphur oxides and, under some conditions, nitrogen oxides. Enzymatic production of biodiesel has been proposed to overcome the drawbacks of the conventional chemically catalyzed processes. The main obstacle facing full exploitation of the enzyme, lipase, potential is its cost. Therefore, reuse of lipase is essential from the economic point of view, which can be achieved by using the lipase in immobilized form. In addition, immobilized lipase displays improved stability and activity. Common immobilization techniques include attachment to solid supports and entrapment within the matrix of a polymer. This article presents a comparison between conventional processes and enzymatic processes and different possible feedstocks for biodiesel production. In addition, possible ways to overcome the problems facing the use of lipase are described. © 2007 Society of Chemical Industry and John Wiley & Sons, Ltd
Biodiesel is a renewable fuel conventionally prepared by transesterification of pre-extracted vegetable oils and animal fats of all resources with methanol, catalyzed by strong acids or bases. This paper reports on a novel biodiesel production method that features acid-promoted direct methanolysis of cellular biomass of oleaginous yeasts and filamentous fungi. The process was optimized for tuning operation parameters, such as methanol dosage, catalyst concentration, reaction temperature and time. Up to 98% yield was reached with reaction conditions of 70 °C, under ambient pressure for 20 h and a dried biomass to methanol ratio 1:20 (w/v) catalyzed by either 0.2 mol L−1 H2SO4 or 0.4 mol L−1 HCl. Cetane numbers for these products were estimated to range from 56 to 59. This integrated method is thus effective and technically attractive, as dried microbial biomass as feedstocks omits otherwise tedious and time-consuming oil extraction processes. Copyright © 2007 Society of Chemical Industry
The effects of silicon deficiency on the metabolism and composition of lipids in Cyclotella cryptica T13L Reimann, Lewin, and Guillard were examined. Silicon-deficient cells had higher levels of neutral lipids (primarily triacylglycerols) and higher proportions of saturated and monounsaturated fatty acids than silicon-replete cells. After 4 h of silicon deficiency, the percentage of newly assimilated NaH14CO3 partitioned into lipids increased from 27.6% to 54.1%, whereas the percentage partitioned into chrysolaminarin decreased from 21.6% to 10.6%. In addition, pulse-chase experiments with NaH14CO3 indicated that the amount of 14C in the total cellular lipid fraction increased by 32% after 12 h of silicon deficiency despite the absence of additional photoassimilable 14C. Therefore, the accumulation of lipids in response to silicon deficiency appears to be due to two distinct processes: (a) an increase in the proportion of newly assimilated carbon partioned into lipids, and (2) a slow conversion of previously assimilated carbon from non-lipid compounds into lipids
Triacylglycerols (TAGs) from microalgae have the potential to be used for biodiesel, but several technical and economic hurdles have to be overcome. A major challenge is efficient extraction of intracellular TAGs from algae. Here we investigate the use of enzymes to deconstruct algal cell walls/membranes. We describe a rapid and simple assay that can assess the efficacy of different enzyme treatments on TAG-containing algae. By this means crude papain and bromelain were found to be effective in releasing TAGs from the diatom Phaeodactylum tricornutum, most likely because of their cysteine protease activity. Pre-treating algal biomass with crude papain enabled complete extraction of TAGs using heptane/isopropyl alcohol. Heptane as a single solvent was also effective, although complete recovery of TAG was not obtained. Economic implications of these findings are discussed, with the aim to reduce the complexity of, and energy needed in, TAG extraction.
The objective of this study was to examine the differences in the biochemical and elemental stoichiometry of a freshwater centric diatom, Stephanodiscus minutulus (Grun.), under various nutrient regimes. Stephanodiscus minutulus was grown at μmax or 22% of μmax under limitation by silicon, nitrogen, or phosphorus. Cell sizes for nutrient-limited cultures were significantly smaller than the non-limited cell sizes, with N-limited cells being significantly smaller than all other treatments. Compared with the nutrient-replete treatment, both carbohydrates and lipids increased in Si- and P-limited cells, whereas carbohydrates increased but proteins decreased in N-limited cells. All of the growth-limited cells showed an increase of carbohydrate and triglyceride, and a decrease of cell size and polar lipids as a percentage of total lipids. The non-limited cells also had a significantly higher chl a concentration and galactolipids as a percentage of total lipids than any of the limited treatments, and the low-Si and low-P cells had significantly higher values than the low-N cells. The particulate C concentrations showed significant differences between treatments, with the Si- and P-limited treatments being significantly higher than the N- and non-limited treatments. Particulate Si did not show a strong relationship with any of the parameters measured, and it was the only parameter with no differences between treatments. The low-Si cells had a significantly higher P content (about two times more) than any other treatment, presumably owing to the luxury consumption of P, and a correspondingly high phospholipid concentration. The elemental data showed that S. minutulus had a high P demand with low optimum N:P (4) and Si:P (10) ratios and a C:N:P ratio of 109:16:2.3. The particulate C showed a positive relationship with POM (r = 0.93), dry weight (r = 0.88), lipid (r = 0.87) and protein (r = 0.84, all P < 0.0001). Particulate N showed a positive relationship with galactolipids (r = 0.95), protein (r = 0.90), dry weight (r = 0.78), lipid (r = 0.75), and cell volume (r = 0.64, all P < 0.0001). It is evident that nutrient limitation in the freshwater diatom S. minutulus has pronounced effects on its biochemical and elemental stoichiometry.
Fossil fuels developed from ancient deposits of organic material, and thus can be thought of as a vast store of solar energy from which society meets >80% of its current energy needs. Here, using published biological, geochemical, and industrial data, I estimate the amount of photosynthetically fixed and stored carbon that was required to form the coal, oil, and gas that we are burning today. Today's average U.S. Gallon (3.8 L) of gasoline required approximately 90 metric tons of ancient plant matter as precursor material. The fossil fuels burned in 1997 were created from organic matter containing 44 1018 g C, which is>400 times the net primary productivity (NPP) of the planet's current biota. As stores of ancient solar energy decline, humans are likely to use an increasing share of modern solar resources. I conservatively estimate that replacing the energy humans derive from fossil fuels with energy from modern biomass would require 22% of terrestrial NPP, increasing the human appropriation of this resource by 50%.
Genetic transformation of two species of diatoms has been accomplished by introducing chimeric plasmid vectors containing
a bacterial antibiotic resistance gene driven by regulatory sequences from the acetyl-CoA carboxylase (ACCase) gene from the
diatomCyclotella cryptica. The recombinant DNA integrated into one or more random sites within the algal genome and the foreign protein was produced
by the algal transformants. This is the first report of genetic transformation of any chlorophyll c-containing microalgal
strain. We are using this system to introduce additional copies of the ACCase gene into diatoms in an attempt to manipulate
lipid accumulation in transformed strains.
We report the genetic transformation of two marine diatoms by microparticle bombardment. The pennate diatom Phaeodactylum tricornutum was transformed with the bacterial gene Sh ble from Streptoalloteichus hindustanus, which confers resistance to the antibiotics phleomycin and zeocin. Transformants contained between 1 and 10 copies of the
exogenous DNA integrated into the genome by illegitimate recombination at apparently random locations. Transformation efficiencies
were around 10−6, and individual cell lines could be maintained at −80°C following cryopreservation. Also, P. tricornutum could be transformed simultaneously with two different plasmids, one containing the Sh ble gene and another containing the firefly luciferase gene (LUC) under control of a promoter derived from a fucoxanthin, chlorophyll a/c-binding protein gene (FCP). In these cotransformants, LUC activity was light inducible. The transient transformation of the centric diatom Thalassiosira weissflogii with the bacterial β-glucuronidase (GUS) gene has also been achieved using similar transformation technology. The availability of gene transfer protocols for marine
diatoms, together with a range of functional reporter genes and regulated expression systems, will permit molecular dissection
of their biology and allow an assessment of the biotechnological potential of these organisms.
Biodiesel is a fuel comprising mono-alkyl esters of medium to long-chain fatty acids derived from vegetable oils or animal
fats. Typically, engines operated on soybean-based biodiesel exhibit higher emissions of oxides of nitrogen (NOx) compared
with petroleum diesel. The increase in NOx emissions might be an inherent characteristic of soybean oil’s polyunsaturation,
because the level of saturation is known to affect the biodiesel’s cetane number, which can affect NOx. A feedstock that is
mostly monounsaturated (i.e. oleate) helps to balance the tradeoff between cold flow and oxidative stability. Genetic modification
has produced a soybean event, designated 335-13, with a fatty acid profile high in oleic acid (>85%) and with reduced palmitic
acid (<4%). This high-oleic soybean oil was converted to biodiesel and run in a John Deere 4045T 4.5-L four-stroke, four-cylinder,
turbocharged direct-injection diesel engine. The exhaust emissions were compared with those from conventional soybean oil
biodiesel and commercial No. 2 diesel fuel. There was a significant reduction in NOx emissions (α=0.05) using the high-oleic soybean biodiesel compared with regular soybean oil biodiesel. No significant differences were
found between the regular and high-oleic biodiesel for unburned hydrocarbon and smoke emissions.
The evolution of large marine mammals and their invasion of the pelagic realm is tied to the availability of sufficient food, which in turn is linked to upwelling areas and other highly productive regions in the ocean, as has been recognized for some time. Here I propose that silicate-supported upwelling (which provides the shorter food chain and hence the higher yield for apex consumers) and deep mixing within the Southern Ocean are the crucial ingredients of the system providing the stage for the evolution of whales. The Circumpolar Current receives silicate from various sources but especially from the North Atlantic Deep Water introduced in the Atlantic sector. The silicate is largely trapped in the Ring, some in the water, and some in the sediment, and is made available to shallower waters by unusually deep mixing. From these shallower depths silica-rich waters can enter the thermocline all through the southern hemisphere, stimulating diatom growth in upwelling systems to the equator and beyond. From the link diatoms–krill–whales and diatoms–krill–small fishes, it is readily apparent that the link between the climate narrative and the narrative of whale evolution (both for mysticetes and odontocetes) is the silica cycle. Studying it will generate hypotheses about whale evolution that can be tested using fossils.
The growth and nutritional content of four tropical Australian microalgal species, diatom Chaetoceros sp. (CS256), two cryptomonads, Rhodomonas sp. (NT15) and Cryptomonas sp. (CRFI01) and unidentified prymnesiophyte (NT19), cultured at five different temperatures, were studied. Commercially available Isochrysis sp. (clone T.ISO) was included in the study for comparison. Microalgae were grown in laboratory 1.5-l batch cultures in F/2 medium at 25, 27, 30, 33 and 35 °C (salinity 25‰; pH 8.3; photon flux density 80 μmol photon m−2 s−1; 12:12 h light:dark cycle). Microalgal cells were harvested in late logarithmic growth phase and analysed for protein, carbohydrate, lipid, chlorophyll a, inorganic matter (ash) and fatty acid composition. The optimum temperature for growth was 25–27 °C for Rhodomonas sp. (specific growth rate, μ=0.27 day−1), and 27–30 °C for prymnesiophyte NT19, Cryptomonas sp., Chaetoceros sp. and Isochrysis sp. (μ=0.56, 0.33, 0.87 and 0.97 day−1, respectively). Only Chaetoceros sp. grew well at 33 and 35 °C (μ>0.78 day−1). All tropical Australian species had significantly lower percentages of protein when cells were grown at temperatures above 27 °C, but there was no consistent trend in the percentages of carbohydrate. Chaetoceros sp. had highest percentage of lipid (16.8% dry weight; P<0.01), when cells were cultured at 25 °C, while Rhodomonas sp., Cryptomonas sp., NT19 and Isochrysis sp., had significantly higher amounts of lipid at temperatures within the range 27–30 °C (15.5, 12.7, 21.4, and 21.7% dw, respectively; P<0.05 in each case). Considering all species together, there was no overall relationship between percentage of protein, carbohydrate or lipid and temperature, but there was an overall, linear relationship between percentage of ash (inorganic matter) and temperature (r2=0.42, P≤0.05). Highest calculated energy values were found in Chaetoceros sp. (21.9 kJ g−1) and Tahitian Isochrysis sp. (22.5 kJ g−1) cultured at 27–30 °C. There was no significant change in chlorophyll a (range 1.2–1.68 pg cell−1) for any species over the temperature range studied.The highly unsaturated fatty acid (HUFA), eicosapentaenoic acid, 20:5n−3, was present in all species, with highest amounts in prymnesiophyte NT19 (19.9% total fatty acids). Percentages of 20:5n−3 were slightly lower at highest growth temperatures for all species. The control, Isochrysis sp., had the highest amount of docosahexaenoic acid, 22:6n−3 (6.6% total fatty acids). All species had lower percentages of 22:6n−3 at higher growth temperatures. Chaetoceros sp. and NT19 had moderate amounts of arachidonic acid, 20:4n−6 in the fatty acid profile (2.7–5.4% total fatty acids). Highest percentages were associated with growth temperatures within the range 27–30 °C. Only Chaetoceros sp. grew well at 35 °C, maintaining moderate percentages of protein, carbohydrate, lipid, PUFA and HUFA (9.6% total fatty acids), at that temperature. All tropical Australian species performed better than Isochrysis sp., in terms of percentage of HUFA, over the range of growth temperatures.