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Biomaterial composition of the microalga Coelastrella sp. (MH923012): Effect of carbon source
Abstract
The effect of carbon source on the internal organic composition of microalga Coelastrella sp. (MH923012), was addressed in the present study. Five to twenty-five milliliter, with increment 5 ml, of aqueous carbon source were dosing into two groups of cultivation flasks, unadjusted pH flasks group and adjusted pH flasks group. The results demonstrated that the improvement in the specific growth rate depends on how many dosing times of the carbonic solution added to the cultivation flasks. Furthermore, the balanced organic structure of the cell is affected by the amount of carbonate source available in the culture media. For instance, dosing of 25 ml of aqueous carbon dioxide solution has led to product 20.3% of lipids, 41.5% of proteins, and 30.1% of carbohydrates compared with that produce from the control flasks composition14.2 % of lipids, 27.7% of proteins, and 50.7% of carbohydrates. The experimental data also showed a significant increase in saturated and unsaturated fatty acids if the dosage were increased. In addition, adjusting the pH did not have a great effect on the rate of specific growth. However, the internal organic composition of microalgal cells has been affected by that adjustment. Therefore, the current study emphasizes the importance of adopting the carbon source as an important factor in the productivity and selectivity bioprocesses in microalgal cells.
... In Coelastrella sp. (MH923012), such a study was carried out to investigate the influence of carbon sources on the internal organic composition of the algae [26]. The specific growth rate depends on dosing times of the carbonic solution added to the culture [1]. ...
... The lipids and proteins increase with increasing aqueous carbon source dosing times, while the carbohydrate content decreases [1]. The data showed that saturated and unsaturated fatty acids significantly improved with increasing dosage [26]. As a result, the carbon source is a critical parameter for algal growth. ...
... MH923012, it is observed that an increase in the dosing times of aqueous carbon solution increases the percentage of lipids. Dosing 5, 10, 15, 20, and 25 ml of aqueous carbon solution resulted in lipid yields of 14.7, 15.1, 18.4, 19, and 20.3%, respectively, compared to 14.2% in control flasks [26]. Coelastrella sp. ...
In the algae industry, product development based on the biorefinery idea is gaining attraction. In today’s world, bioactive chemicals generated from microalgae are extremely important. Its industrial significance has extended which includes various high-value chemicals in addition to primary biomass. The importance of Coelastrella sp., a less studied green microalgae, for the biorefinery technique is discussed in this review. Industries recently used microalgal feedstocks to help them cope with the rising energy issue. High-value co-products can be produced from algal biomass combined with biofuel to improve the economics of a microalgal biorefinery was emphasised. Coelastrella sp. becomes a significant substrate to investigate in this regard. Coelastrella is a better renewable energy resource feedstock. A total of 18% of their biomass is made up of lipids. Coelastrella sp. has a greater concentration of C18:1, which is beneficial for biodiesel conversion. Furthermore, Coelastrella sp. was discovered to be effective in bioremediation, absorbing nutrients from wastewater to produce lipids and carotenoids. Single product extraction is not economically feasible for industrial practices. In this view, the number of bioactive compounds extracted from Coelastrella sp. relevant to the biorefinery concept is emphasised. Enhancing the production of algal biomass, on the other hand, is one of the industry’s primary concerns. When it comes to artificial lighting and determining the best culture parameters, algal culture appears to be costly. This review discusses the challenges encountered in the biorefinery approach to produce Coelastrella biomass and the future prospects of Coelastrella sp. for various applications.
Graphical abstract
... The growing energy demand led to a search for high efficiency, low cost, and sustainable energy sources. Utilizing renewable energy sources can play a major role in a partial replacement of conventional energy (Razooki et al, 2020;Al-Mashhadani et al. 2016). One of the most potential energy sources is the fuel cell, which still does not subsidize the growing energy demands (Zhang et al. 2010). ...
Renewable energy such as microbial fuel cell may be an important promising potential alternative source to conventional fuels in energy production as well as wastewater treatment. In the present article, the sediment sludge in microbial fuel cell was adopted for generating electricity. The experimental data illustrated that the organic contents of the sludge sample have a major impact on the produced power despite the low bacterial presence. It was shown that a 38% increase in the organic content resulted a 86% increase in generated power. Doubling electrodes surface area increased generated power by 40% for the anode and 60% for the cathode. In addition, introducing excessive oxygen to both anode and cathode chambers has a negative impact and decreased the power by 30% especially with the presence of oxygen in the anode chamber. Connecting cells in series increased internal resistance, but overall produced power was increased by almost 30%. A distance of 8–10 cm between anode and cathode was found to be optimum. In addition, the results also showed that the system exposure to oxygen continuously causes a decrease in the amount of energy generated due to the influence of the anaerobic environment in the anode region. With a continuous run of sediment microbial fuel cell for the duration of 4 days, a stable increasing rate of power generation was achieved.
The activity and growth of microorganisms for renewable energy production are still influenced by the dead zones created in bioreactors. These areas form a nutrient and thermal gradient, causing an abundance of food in certain areas compared to famines in other areas of same bioreactor. The current study is a step in identifying those dead zones, followed by another step in improving the flow of media inside the reactor. The results indicated that the inner parts of the bioreactor may be a crucial factor in the creation and spread of such dead zones. For example, the position of the disc-type diffuser contributes to the generation of those areas at the bottom of the reactor. It was inferred from the fluid movement in reactors using the annular-type diffuser proposed in the current study. The bubble size, gas mass flux, and radiuses of fillet, as the most important factors, were examined in both bioreactors. The results revealed a noticeable improvement in these parameters in this area of the reactor when the disc diffuser was replaced by the annular diffuser. For example, the average liquid velocity was recorded in the lower part of the modernized reactor at 0.0198 m/s, while the velocity was recorded in the conventional reactor at 0.00077 m/s under same bubbles diameter used in both reactors (0.125 mm). The inclusion of the effect of the presence of microorganisms in mathematical models was also addressed in the current study. The results showed that the amount of oxygen remaining at the bottom of the reactor after bio-consumption in the presence of the annular diffuser was higher than that in the conventional reactor. This clearly emphasizes the importance of the design of the internal parts of the bioreactor.
Conventional identification of three coccoid green algae isolates was attempted to characterize the studied algae morphologically under compound microscope, which demonstrated confusional phenomenal convergence; all were classified microscopically as the green alga Chlorella vulgaris Beijerinck, 1890.
Phylogenetic studies were conducted to settle the argument about the phenotype by studying the genotype. Genotype the promising field in advance classification by using 18S rRNA and compared to GenBank database using to search the related sequences. The determined sequences showed high a similarity to the strains registered in GenBank.
Phylogenetic tree of ITS within 18S RNA were analyzed: the phylogram separated into two clusters, the first cluster included C1-ITS-Iraq and C2-ITS-Iraq and put with Coelastrella Chodat, 1922 which was well supported in bootstrap tests (86-100%), while the second cluster included C3-ITS-Iraq and put with C. sorokiniana Shihira and Krauss, 1965, which have bootstrap value 100% with the mentioned species. however, in this study, the green alga Colestrella was identified as new record genus in Iraqi freshwater belonged to the order Sphaeropleales.
The present paper addresses cultivation of Chlorella vulgaris microalgae using airlift photobioreactor that sparged with 5% CO 2 /air. The experimental data were compared with that obtained from bioreactor aerated with air and unsparged bioreactor. The results showed that the concentration of biomass is 0.36 g l -1 in sparged bioreactor with CO2/air, while, the concentration of biomass reached to 0.069 g l -1 in the unsparged bioreactor. They showed also that aerated ioreactor.with CO2/air gives more biomass production even the bioreactor was aerated with air. This study proved that application of sparging system for ultivation of Chlorella vulgaris microalgae using either CO2/air mixture or air has a significant growth rate, since the bioreactors become more thermodynamically favorable and provide impetus for a higher level of production.
biofixing process
In order to mitigate the well-being impacts of climate change effectively, we must reduce our use of fossil fuels. However, many contemporary forms of well-being attainment still depend heavily on the use of fossil fuel derived energy. Therefore, certain necessary forms of climate change mitigation are likely to conflict with current means of well-being attainment in many groups and societies. In particular our concern is that certain forms of mitigation, which target lifestyle choices, consumption behaviour, and technological choices, do and will have disproportionate impacts on certain vulnerable groups in society e.g. households in fuel poverty or individuals with particular disabilities. It is evident that climate change mitigation discourse has only sparsely integrated well-being thought. We argue that a fuller integration of well-being into mitigation thinking could help avoid exacerbating current and future well-being conflicts that will arise between climate change mitigation and fossil fuel derived use.
To help achieve this, we reason that climate change mitigation and fossil fuel derived use must not be viewed separately but by their relationships to well-being. We articulate the individual processes of fossil fuel derived energy use, climate change mitigation and well-being attainment in more detail, presenting their relationships to one another in the form of tensions. We present a capabilities conception of well-being that we argue is best suited for operationalising well-being with regards to fully capturing these tensions. We then develop a conceptual framework through a theoretical synthesis of existing on well-being, energy, and climate change, which illustrates how these tensions arise. This framework also serves to illustrate how a change in one process will affect the others. We outline how this framework can help illustrate the points at which misguided climate change mitigation can conflict with current means of attaining well-being from fossil derived energy. We then conclude that the use of this framework and further integration of well-being thought could help avoid and ameliorate well-being conflicts when developing future climate change mitigation.
Photosynthetic protists, also called microalgae, have been systematically studied for more than a century. However, only recently broad biotechnological applications have fostered a novel wave of research on their potentialities as sustainable resources of renewable energy as well as valuable industrial and agro-food products. At the recent VII European Congress of Protistology held in Seville, three outstanding examples of different research strategies on microalgae with biotechnological implications were presented, which suggested that integrative approaches will produce very significant advances in this field in the next future. In any case, intense research and the application of systems biology and genetic engineering techniques are absolutely essential to reach the full potential of microalgae as cell-factories of bio-based products and, therefore, could contribute significantly to solve the problems of biosustainability and energy shortage.
Many microorganisms possess inducible mechanisms that concentrate CO2 at the carboxylation site, compensating for the relatively low affinity of Rubisco for its substrate, and allowing acclimation to a wide range of CO2 concentrations. The organization of the carboxysomes in prokaryotes and of the pyrenoids in eukaryotes, and the presence of membrane mechanisms for inorganic carbon (Ci) transport, are central to the concentrating mechanism. The presence of multiple Ci transporting systems in cyanobacteria has been indicated. Certain genes involved in structural organization, Ci transport and the energization of the latter have been identified. Massive Ci fluxes associated with the CO2-concentrating mechanism have wide-reaching ecological and geochemical implications.
The use of liquid fossil fuel as an energy source has long been considered unsustainable and most importantly the liquid fossil fuel will be diminished by the middle of this century. In addition, the fossil fuel is directly related to environmental degradation and greenhouse emission. Biofuel produced from plants, animals or algae products can offer an alternative to reduce our dependency on fossil fuel and assist to maintain healthy global environment. Micro-algae is becoming popular candidate for biofuel production due to their high lipid contents, ease of cultivation and rapid growth rate. This paper reviews the current state-of-the-art of biofuel from algae as a renewable energy source.
Oleic acid is a common pharmaceutical excipient that has been widely used in various dosage forms. Gas chromatography (GC) has often been used as the quantitation method for fatty acids normally requiring a derivatization step. The aim of this study was to develop a simple, robust, derivatization-free GC method that is suitable for routine analysis of all the major components in oleic acid USP-NF(⁎) material. A gas chromatography - flame ionization detection (GC-FID) method was developed for direct quantitative analysis of oleic acid and related fatty acids in oleic acid USP-NF material. Fifteen fatty acids were separated using a DB-FFAP (nitroterephthalic acid modified polyethylene glycol) capillary GC column (30 m×0.32 mm I.D) with a total run time of 20 min. The method was validated in terms of specificity, linearity, precision, accuracy, sensitivity, and robustness. The method can be routinely used for the purpose of oleic acid USP-NF material analysis.
Biodiesel production by microalgae with photosynthetic CO2 biofixation is thought to be a feasible way in the field of bioenergy and carbon emission reduction. Knowledge of the carbon-concentrating mechanism plays an important role in improving microalgae carbon fixation efficiency. However, little information is available regarding the dramatic changes of cells suffered upon different environmental factors, such as CO2 concentration. The aim of this study was to investigate the growth, lipid accumulation, carbon fixation rate, and carbon metabolism gene expression under different CO2 concentrations in oleaginous Chlorella. It was found that Chlorella pyrenoidosa grew well under CO2 concentrations ranging from 1 to 20 %. The highest biomass and lipid productivity were 4.3 g/L and 107 mg/L/day under 5 % CO2 condition. Switch from high (5 %) to low (0.03 %, air) CO2 concentration showed significant inhibitory effect on growth and CO2 fixation rate. The amount of the saturated fatty acids was increased obviously along with the transition. Low CO2 concentration (0.03 %) was suitable for the accumulation of saturated fatty acids. Reducing the CO2 concentration could significantly decrease the polyunsaturated degree in fatty acids. Moreover, the carbon-concentrating mechanism-related gene expression revealed that most of them, especially CAH2, LCIB, and HLA3, had remarkable change after 1, 4, and 24 h of the transition, which suggests that Chlorella has similar carbon-concentrating mechanism with Chlamydomonas reinhardtii. The findings of the present study revealed that C. pyrenoidosa is an ideal candidate for mitigating CO2 and biodiesel production and is appropriate as a model for mechanism research of carbon sequestration.
Thedegree ofunsaturation offatty acids washigher inChIo- rella vulgaris 1hcells grownwithair(low-CO2 cells) thaninthe cells grownwithairenriched with2% CO2(high-CO2 cells). The change intheratio oflinoleic acidtoa-linolenic acidwaspartic- ularly significant. Thischange oftheratio wasobserved infour majorlipids (monogalactosyldiacylglycerol, digalactosyldiacyl- glycerol, phosphatidylcholine, andphosphatidylethanolamine). Therelative contents oflipid classes wereessentially thesame bothinhigh-CO2 andlow-CO2 cells. After high-CO2 cells were transferred tolowCO2condition, total amountoffatty acids remained constant buttherelative content ofa-linolenic acid increased during a6-hour lagphaseingrowth withconcomitant decreases inlinoleic andoleic acids. Whenlow-CO2 cells were transferred tohighCO2condition, total amountoffatty acids and relative content ofoleic acidincreased significantly. Theamount ofa-linolenic acidremained almost constant, while theamounts ofpalmitic, oleic, andlinoleic acidsincreased. Similar, but smaller, changes infatty acidcompositions wereobserved intwo species ofgreenalgae Chiamydomonas reinhardtii andDunalieiia tertiolecta. However, nodifference wasfound inEuglena gracilis, Porphyridium cruentum, Anabaenavariabilis, andAnacystis nidulans.
Future scenarios with significant anthropogenic climate change also display large increases in world production of fossil fuels, the principal CO2 emission source. Meanwhile, fossil fuel depletion has also been identified as a future challenge. This chapter reviews the connection between these two issues and concludes that limits to availability of fossil fuels will set a limit for mankind's ability to affect the climate. However, this limit is unclear as various studies have reached quite different conclusions regarding future atmospheric CO2 concentrations caused by fossil fuel limitations.
It is concluded that the current set of emission scenarios used by the IPCC and others is perforated by optimistic expectations on future fossil fuel production that are improbable or even unrealistic. The current situation, where climate models largely rely on emission scenarios detached from the reality of supply and its inherent problems are problematic. In fact, it may even mislead planners and politicians into making decisions that mitigate one problem but make the other one worse. It is important to understand that the fossil energy problem and the anthropogenic climate change problem are tightly connected and need to be treated as two interwoven challenges necessitating a holistic solution.
Microalgal biomass seems to be a promising feedstock for biofuel generation. Microalgae have relative high photosynthetic efficiencies, high growth rates, and some species can thrive in brackish water or seawater and wastewater from the food- and agro-industrial sector. Today, the main interest in research is the cultivation of microalgae for lipids production to generate biodiesel. However, there are several other biological or thermochemical conversion technologies, in which microalgal biomass could be used as substrate. However, the high protein content or the low carbohydrate content of the majority of the microalgal species might be a constraint for their possible use in these technologies. Moreover, in the majority of biomass conversion technologies, carbohydrates are the main substrate for production of biofuels. Nevertheless, microalgae biomass composition could be manipulated by several cultivation techniques, such as nutrient starvation or other stressed environmental conditions, which cause the microalgae to accumulate carbohydrates. This paper attempts to give a general overview of techniques that can be used for increasing the microalgal biomass carbohydrate content. In addition, biomass conversion technologies, related to the conversion of carbohydrates into biofuels are discussed.
Algae are considered as a promising source for biofuel and bio-products. Algae contain carbohydrates, lipids, proteins and their photosynthetic and lipid accumulating potential makes them a suitable candidate for bioenergy. Algal biomass is used in the production of biofuels like biodiesel, bioethanol, biobutanol, and biohydrogen etc. Therefore, this review provides an overview on the usage of algal biomass in multiple applications like fuel, food and environment. Initially, evolution of first and second generation biofuel feedstocks and their limitations have been described. Later, advantages of third generation biofuel feedstock i.e., algae over first and second generation feedstock were discussed comprehensively. Apart from bioenergy production from algae, industrially important co-products or value added products extracted from microalgae were addressed. Various microalgae utilized for the extraction of omega-3 fatty acids were listed. Eventually, environmental application of microalgae namely wastewater treatment and CO2 sequestration were presented.
Copper tolerance in Anabaena doliolum has been studied by comparing the physiological properties of its wild type and Cu-tolerant strains. A concentration dependent reduction in growth, pigments, protein, sugar, lipid and ATP content, photosynthetic electron transport chain, O2-evolution, carbon fixation, nutrient uptake (NH+4 and NO--3), nitrate reductase, nitrogenase, glutamine synthetase and alkaline phosphatase activities was noticed in both the strains following Cu-supplementation. The reduction in all parameters was higher in wild type than the tolerant strain. The latter produced a larger (19.5 %) lipid fraction than the wild type even in the absence of added metal. As compared to the wild strain, the tolerant strain showed enhanced enzyme activities, especially of alkaline phosphatase (20 % higher), low copper uptake and insignificant loss of K+ and Na+. The data on lipid production, loss of K+ and Na+, and uptake of copper collectively indicate a change in the permeability of the plasma membrane and a possible operation of «exclusion mechanism» in the tolerant strain thereby reducing the toxic effect of copper even at a high concentration.
Carbon dioxide is one of the most common gases produced from biological processes. Removal of carbon dioxide from these processes can influence the direction of biological reactions as well as the pH of the medium, which affects bacterial metabolism. Kinetics of carbon dioxide transfer mechanisms are investigated by sparging with conventional fine bubbles and microbubbles. The estimate of the concentrations of CO2(aq), H2CO3, HCO3 –, and CO32– from pH measurement in an airlift loop sparged mixer is derived. The canonical estimate of overall mass transfer coefficient of CO2 has been estimated as 0.092 min–1 for a microbubble size of 550 m compared with 0.0712 min–1 for a fine bubble (mean bubble size of 1.3 mm) sparging. It is observed that the efficiency of CO2 removal has increased up to 29% by microbubble sparging compared with fine bubble sparging. Laminar bubbly flow modeling of the airlift loop configuration correctly predicts the trend of the change in overall mass transfer in both gas stripping with nitrogen and gas scrubbing for CO2 exchange, while demonstrating the expected separated flow structure. The models indicate that the macroscale flow structure is transient and pseudoperiodic. This latter feature should be tested by flow visualization, as preferential frequencies in the flow can be exploited for enhanced mixing.
Marine microalgae were studied as potential resources for the production of biodiesel. Five marine microalgae, Tetraselmis suecica, Phaeodactylum tricornutum, Chaetoceros calcitrans, Isochrysis galbana, and Nannochloropsis oculata were cultured in f/2 media, 12:12 L:D cycle at 20 ± 1°C with a light intensity of 36.3 μmol/m2/sec using a 15-L circular cylindrical photobioreactor. The dry cell weight, specific growth rate, biomass productivity, oil
content and fatty acid composition of palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid of microalgae
were determined. T. suecica, I. galbana, and N. oculata showed high dry cell weights of 0.58, 0.57, and 0.57 g/L, respectively. The culture period of T. suecica to reach the stationary phase was 9 days. On the other hand, N. oculata showed the longest culture period of 28 days to reach the stationary phase. T. suecica absorbed nitrate at the initial stages of cell growth, decreasing the nitrate concentration to 0.5 mg/L on day-7 of the culture.
The highest oil contents were observed in P. tricornutum with a 25.31% dry cell weight and I. galbana with a 23.15% dry cell weight on day-9 after the stationary phase. I. galbana showed 417.33 mg of palmitic acid per g oil and T. suecica showed 235.61 mg of oleic acid per g oil. Stearic acid, linoleic acid, and linolenic acid did not exceed 30.02 mg/g oil in
any of the microalgae. T. suecica showed the shortest culture period of 9 days to reach the stationary phase. Therefore, the highest biomass production of
0.58 g/L was obtained and I. galbana showed high biomass production of 0.57 g/ L and oil content of 23.15% of dry cell weight. Therefore, T. suecica and I. galbana can be selected as a potential candidate for the production of biodiesel.
Keywordsbiodiesel–microalgae–oil contents–fatty acids
Structure and properties of pyrenoid and stroma starch were compared in Chlorella. To obtain pyrenoid starch- and stroma starch-enriched samples of high purity, we investigated the effects of the CO2 concentration and growth phase on the intracellular amount and localization of starch. In cells grown with air containing 3% CO2 (high-CO2 cells) at the log phase, starch was accumulated primarily as stroma starch. When these high-CO2 cells were transferred to low-CO2 conditions (air level, 0.04% CO2), pyrenoid and pyrenoid starch started to develop within several hours. After 12 h, the amount of starch per cell had increased to about 2.5-fold of that in the high-CO2 cells, the size of starch granules drastically increased (about 2.5-fold in diameter), and the morphology changed from discoidal to cup-shaped, suggesting that the cells predominantly contained pyrenoid starch. The starch composition and chain-length distribution profile did not change so much within 12 h. However, analysis of the starch with a differential scanning calorimeter demonstrated that the peak temperature of gelatinization was significantly decreased as compared with that in the high-CO2 cells. These findings suggest that pyrenoid and stroma starch have distinctive physicochemical properties that are caused by the difference in the water absorption and swelling ratio of starch granules mainly due to the difference in the morphology.
Study of increasing lipid production from fresh water microalgae Chlorella vulgaris was conducted by investigating several important factors such as the effect of CO2 concentration, nitrogen depletion and harvesting time as well as the method of extraction. The drying temperature during lipid extraction from algal biomass was found to affect not only the lipid composition but also lipid content. Drying at very low temperature under vacuum gave the best result but drying at 60 °C still retained the composition of lipid while total lipid content decreased only slightly. Drying at higher temperature decreased the content of triacylglyceride (TG). As long as enough pulverization was applied to dried algal sample, ultrasonication gave no effect whether on lipid content or on extraction time. In addition to the increase of total lipid content in microalgal cells as a result of cultivating in nitrogen depletion media, it was found that changing from normal nutrient to nitrogen depletion media will gradually change the lipid composition from free fatty acid-rich lipid to lipid mostly contained TG. Since higher lipid content was obtained when the growth was very slow due to nitrogen starvation, compromising between lipid content and harvesting time should be taken in order to obtain higher values of both the lipid content and lipid productivity. As the growth was much enhanced by increasing CO2 concentration, CO2 concentration played an important role in the increase of lipid productivity. At low until moderate CO2 concentration, the highest lipid productivity could be obtained during N depletion which could surpassed the productivity during normal nutrition. At high-CO2 concentration, harvesting at the end of linear phase during normal nutrition gave the highest lipid productivity. However, by reducing the incubation time of N depletion, higher lipid content as well as higher lipid productivity may still be achieved under this condition.
Participation in laboratory evaluating programmes (Proficiency Testing schemes) is becoming increasingly important, especially for accredited laboratories. The Wageningen Agricultural University meets this need by organizing several world‐wide international laboratory evaluating programmes on chemical analysis of soils (ISE), plants OPE), manure, refuses (MARSEP) and sediments (SETOC). Since 1995, the existing programmes have been placed under an umbrella organization called WEPAL: Wageningen Evaluating Programmes for Analytical Laboratories. Because of the increasing importance of a good performance within the Proficiency Testing scheme, it is crucial that the organizer of the programmes can continue to guarantee a quality product. To achieve this, WEPAL reorganized and documented the complete system in order to get a formal accreditation (based on ISO/IEC Guide 43, part 1) as a qualified organizer of proficiency testing schemes. Much attention was paid to the topic of homogeneity and stability of the distributed materials. Based on a comparison of results obtained by i) participants of the schemes, ii) the Central Laboratory of the Sub‐department Soil Science and Plant Nutrition and iii) a long‐history of results, it may be concluded that the homogeneity and stability of the materials distributed through the ISE‐ and SETOC‐schemes are sufficient for the goal of Proficiency Testing.
In a synchronously grown Chlamydomonas reinhardtii (Chlorophyceae) culture the CO2-concentrating mechanism (CCM) was induced by lowering the CO2 level from 4% to 0.036% CO2 (culture HL). The effects of the reduced carbon supply on starch levels were studied over a period of up to 100 h and compared with control cultures kept either at 4% CO2 (culture H) or continuously at ambient air (0.036% CO2, culture L). Lowering the CO2 supply reduced culture growth as estimated by chlorophyll, protein and cell density. The starch level continued to show diurnal variations with an initially reduced rate of starch synthesis at reduced or abolished culture growth. Subsequently, starch maxima and minima increased. After 4 days the resulting pattern for culture HL was similar to that of culture L, which possessed higher minima but identical maxima to culture H. The intracellular starch localisation was examined on electron micrographs. Cell extracts were assayed for ADP-glucose pyrophosphorylase (EC 2.7.7.27) and starch phosphorylase (EC 2.4.1.1) activities. Over the assayed period of 2 days, there was a good correlation between the observed changes in the starch levels and the measured enzyme activities. The rate of CO2-dependent oxygen evolution of culture HL declined from 100% to 60% of the control over the day. This indicates that the diminished or abolished growth and the impairment of starch accumulation upon CO2 depletion are not simply consequences of the lowered level of the substrate CO2. The diminished growth and the peculiar starch accumulation pattern with higher positions of the starch minima in low-CO2 cells are interpreted as economised starch utilisation as long-term aspects of induction of the CCM.
Continued use of petroleum sourced fuels is now widely recognized as unsustainable because of depleting supplies and the contribution of these fuels to the accumulation of carbon dioxide in the environment. Renewable, carbon neutral, transport fuels are necessary for environmental and economic sustainability. Biodiesel derived from oil crops is a potential renewable and carbon neutral alternative to petroleum fuels. Unfortunately, biodiesel from oil crops, waste cooking oil and animal fat cannot realistically satisfy even a small fraction of the existing demand for transport fuels. As demonstrated here, microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels. Like plants, microalgae use sunlight to produce oils but they do so more efficiently than crop plants. Oil productivity of many microalgae greatly exceeds the oil productivity of the best producing oil crops. Approaches for making microalgal biodiesel economically competitive with petrodiesel are discussed.
- R B Bird
- W E Stewart
- E N Lightfoot
R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, John Wiley &
Sons, 2007.