Journal of Applied Phycology

Microalgae have emerged as promising candidates for the sustainable production of lipids and valuable fatty acids. However, the stress strategies commonly used to enhance lipid accumulation often limit biomass accumulation, posing a significant challenge to maximizing lipid yields. Here, we adopted a two-stage cultivation strategy by separating the biomass accumulating phase at optimum temperature (Phase 1) from the lipid accumulating phase at lower temperatures (Phase 2) for Vischeria sp. WL1. We found that low temperatures at Phase 2 could rapidly induce lipid accumulation within 12 h, reaching the highest content of 61% on day 6 (2 days after transition to Phase 2). The unexpected increase in cellular chlorophyll a content at 9℃ might have facilitated enhanced light energy absorption for lipid accumulation. Our analysis revealed a selective decrease in saturated fatty acids, accompanied by a rise in monounsaturated fatty acids, while polyunsaturated fatty acids remained unchanged under 9℃. Furthermore, fatty acids generally exhibited two distinct patterns at 9℃ after the transition to Phase 2, either increasing or decreasing. Notably, we discovered that the induction of fatty acid accumulation was governed by precise temperature thresholds, with 9℃ showing an induction effect, whereas 15℃ did not. Overall, our study provides practical insights into biomass accumulation, oil production, and selective fatty acid biosynthesis through a temperature-dependent two-stage cultivation strategy.

Pyropia yezoensis is a favourite food and economic crop in East Asia; however, in recent years, its production and economic benefits have been declining. The growth traits of germplasm are fundamental factors determining yield, often closely related to the length-to-width ratio of the blades. In this study, two strains of P. yezoensis with different morphotypes (long and wide blade shapes) were used, and transcriptomic sequencing and analysis were conducted on the top, central, and edge regions of each thallus. The results indicate that although the gene transcription levels are similar among different parts of the same blade shape, significant differences in the abundance of products from photosynthesis-related genes such as psbA and cpcB were observed at the top of the thallus between two blade shapes. Co-expression network analysis identified gene modules significantly positively correlated with the strain of long-blade shape, involving genes such as chlB related to chlorophyll synthesis in photosynthesis, the cytochrome f/b6 complex petA, and the phycocyanin apcE mainly located in chloroplasts or plastids. Therefore, differences in the traits of long and wide blade shapes of P. yezoensis may manifest in photosynthesis-related functions at the top of the thallus. Among the differentially expressed gene sequences of the two blade shapes of P. yezoensis, SSR sites dominated by tri-nucleotide repeats were identified, suggesting the potential for developing EST-SSR markers to distinguish between long and wide blade shapes. Elucidating the gene transcription characteristics associated with blade morphology in P. yezoensis is valuable for identifying and cultivating new high-yield strains of this seaweed.

Microalgal lipids are molecules of biotechnological interest for their application in sustainable food and energy production. However, lipid production is challenged by the time-consuming and laborious monitoring of lipid content in microalgae. This study aimed to predict the lipid content of Chlorella vulgaris cultivations based on non-invasively collected near-infrared (NIR) range hyperspectral data. A gravimetric analysis of total lipids was used as reference data (between 2 and 22% per dry weight) to compare three different models to determining the lipid content. A one-dimensional convolutional neural network and partial least squares models performed at a similar level. Both models could predict the lipid content of Chlorella dry weight with an error of 4%pt (root mean squared error). The index-based linear regression model performed the weakest of the three models, with the error of the prediction being 6%pt. Nile Red staining was used to visualise lipids on a microscope and lipid class analysis to resolve the lipid classes that explained most of the increase in lipids in Chlorella. A SHAP algorithm (SHapley Additive exPlanations) was used to analyse the wavebands of NIR spectra that were important for predicting the total lipid content. The results show that spectral data, when combined with an adequate algorithm, could be used to monitor microalgae lipids non-invasively in a closed system, in a way that has not previously been demonstrated with an imaging system.

Microalgal metabolism is affected by the surrounding environment and nutrients such as phosphorus (P) and nitrogen (N) are essential for optimal metabolism, as well as trace amounts of essential metals such as zinc (Zn); although in higher doses than required, Zn can be toxic. Lead (Pb) is a non-essential metal that can harm organisms from different trophic levels. In the environment, algae are exposed to several stressors simultaneously and adapt their metabolism. In the present study, we evaluated P limitation combined with environmental concentrations of Zn or Pb to the freshwater microalga Raphidocelis subcapitata regarding growth, pigments production, and photosynthetic parameters. Our results indicate that P limitation affected the growth, pigments production, relative maximum electron transport rate (rETRmax), and saturation irradiance; while Pb altered growth, pigments production, and maximum quantum yield; and Zn affected pigment production, photochemical and non-photochemical quenching, and rETRmax. However, the combination of metal and P limitation resulted in synergistic responses, i.e., higher damages than the isolated stressors, in growth, maximum and effective quantum yield, and in the rapid light curve parameters. On the other hand, antagonism, i.e., lower damages than isolated stressors, was observed in pigments production and non-photochemical quenching, suggesting that algae activated defense mechanisms to cope with both stressors simultaneously. In addition, our results indicate an algal metabolism adjustment to P limitation and highlight the importance of considering physicochemical water characteristics when defining regulations of acceptable levels of metals in aquatic ecosystems.

This mini review deals with selected aspects of the health and production of the red algal, agarophyte Gracilaria spp. Amongst common macroalgal diseases in the rhodophytes, “ice-ice” presents itself as perhaps the most common first appearing as an apical tip bleaching phenomenon. This phenomenon is widely studied and reported to be caused by defined bacteria. Regrading grazers, the consumers of Gracilaria are presented with resistance against attack. Finally, harmful epiphytes play a dominant role in Gracilaria production. The review provides information and guidance to aspects of various common pests of Gracilaria such as their attachment, damage caused, preferred conditions and various defense practices against their damaging impacts. Understanding and manipulating the red algal microbiome, under specific and varying cultivation conditions, will be a key factor in the holistic control of disease and pest management.

The invasion of the brown seaweed Rugulopteryx okamurae is altering the equilibrium and reducing the biodiversity of marine coastal ecosystems in southern Europe, with negative economic consequences for fishermen, tourists and governments that regularly remove tons of sediment from the coast. However, the large amount of biomass produced also implies an opportunity for the valorization of these seaweeds, for example in the form of biofertilizer and/or biostimulant for agricultural use. In this study we characterized the biochemical composition of R. okamurae and aqueous extracts. The annual compositional variation of the seaweed was studied by measuring the concentrations of carbohydrates, lipids, proteins, minerals, phenolic compounds, and antioxidants, as well as the concentrations of metals and micro/macroelements, in samples collected in two consecutive years from southern Spain. The composition of the seaweed varied between years for macro/micronutrients, metals, proteins, polyphenols and lipids (mainly terpenes), while polysaccharides (fucoidan, laminarin and alginate) remained at similar concentrations. The seaweed composition highlighted the terpene concentration mainly in 2023. The aqueous extracts significantly increased the fucoidan and laminarin fractions compared to those of the seaweed. Overall, the biochemical characterization results suggest that R. okamurae is valuable as a biofertilizer due to its mineral content (K, Ca, Fe, Mn), while the extract compositions (sulfur, polyphenolic, fucoidan, laminarin, and glycolipid) suggest its potential use as a biostimulant. Thus, this study proposes that R. okamurae is a valuable source for agricultural use.

Natural waters often contain complex mixtures of unknown contaminants, potentially endangering marine communities through chemical interactions. This study presents results demonstrating the toxic effect of zinc oxide nanoparticles in the concentration range of 1.6–12.8 mg L⁻¹ on structural–functional, morphological and biochemical parameters of cells of the diatom Thalassiosira weissflogii. We show that interaction of ZnO NPs with T. weissflogii cells leads to inhibition of cell proliferation, impairment of cell viability, increase in the production of reactive oxygen species and suppression of the photosynthetic apparatus, probably due to mechanical damage of cells, adsorption and aggregation of ZnO NPs on the cell surface. Transfer to fresh nutrient medium after 7 days of exposure at concentrations of 1.6 and 3.2 mg L⁻¹ ZnO NPs resulted in restoration of cell division and increase in rETR, indicating the development of adaptation potential of T. weissflogii to the action of the studied pollutant at the expense of resistant cells. Diatom cells, which became resistant as a result of physiological acclimatisation or emerged by rare spontaneous mutations, demonstrated the ability to self-protection by increasing the activity of the antioxidant system and stabilising enzymatic processes. Such studies and the results obtained in this work are important for the improvement of biotesting techniques for a more adequate and realistic assessment of pollutant toxicity and protection of the aquatic environment.

Microalgae can resist environmental conditions while biodegrading organic pollutants and producing high-value metabolites simultaneously within the cell, thus contributing to the circular economy. Antibiotic stress can cause the accumulation of different types of lipid molecules in microalgal cells, with the potential to be used as biodiesel. The objective of this study was to reveal the streptomycin-treatment-related intracellular metabolite changes and to investigate the potential of microalgae, particularly for biodiesel production under streptomycin stress. Cell growth and photosynthetic activity decreased at two applied concentrations (20 µg mL⁻¹ and 40 µg mL⁻¹) of streptomycin due to the inhibition of the large subunit (LSU) of RubisCo protein. Fourier-transform infrared spectroscopy (FTIR) analysis showed a relative increase in the intracellular carbohydrates and fatty acids. Carotenoid and lipid contents were increased 2.3 and 1.74-fold, respectively. Lipid contents were increased to 51% and 54% in 20 µg mL⁻¹ and 40 µg mL⁻¹ streptomycin treated cultures, respectively, compared to the untreated control (31%). The increase in saturated fatty acid (SFA) content from 47.13% to 56.96%, mainly dominated by Palmitic acid (C16:0) and stearic acid (C18:0) was promising for biodiesel production. The quality predictions based on cetane number, iodine value, and kinematic viscosity were within the set limits of European standards for biodiesel (EN14214). On the other hand, total fatty acid content requirements were only met at the higher dose of streptomycin according to the standard value (≤ 96%). Although antibiotic stress is a relatively new approach for lipid production in microalgae, the findings of this study are considered promising for the utilization of antibiotic wastewater for biodiesel production purposes.

Duration of nitrate starvation exposure induces changes in microalgal nitrogen and carbon metabolism. However, molecular nitrogen and carbon metabolism adjustments remain unclear during nitrate starvation, especially in the non-model chlorophyte microalga, Messastrum gracile SE-MC4. Transcriptome analysis successfully identified 10 and 16 genes significantly affected concerning nitrogen and carbon metabolism, respectively. A short exposure period to nitrate starvation triggered the up-regulation of nitrogen metabolism-related genes. In contrast, a prolonged exposure period to nitrate starvation up-regulated carbon metabolism-related genes. Therefore, a short period of exposure to nitrate starvation was characterized by an increased need to secure nitrogen sources. In contrast, prolonged exposure to nitrate starvation displaces energy metabolism from the plastid to the mitochondria via increased TCA activity. The findings illustrate the stress regulation and defense strategies activated during nitrate starvation.

Microalgae are a diverse collection of unicellular photosynthetic organisms that grow in a wide range of environments, from hot springs to snow and ice. They have great potential for renewable energy generation as well as being potential sources of a wide range of metabolites including lipids, proteins, pigments, and bioactive compounds. Microalgae have received a lot of interest in recent years as a resource for sustainable aquaculture and as a potential solution to the environmental and dietary challenges created by traditional aquaculture practices. Recent biotechnology advancements have enabled scientists to modify the genetic composition of microalgae through CRISPR technology, specifically focusing on genes or metabolic pathways that provide unprecedented accuracy and efficiency for the production of bioactive substances and biorefineries. CRISPR-based microalgal genetic engineering could eventually help to ease pressure on wild fish populations, preserve natural aquatic ecosystems, and improve the nutritional value of farmed fish for human consumption. This review also highlights the challenges and limitations of applying CRISPR technology in microalgae, including the risk of off-target effects that can alter unintended genomic regions, leading to unpredictable outcomes. Likewise, the efficient delivery of CRISPR components into microalgal cells remains a critical challenge, necessitating the development of species-specific delivery methods to enhance the precision and efficacy of CRISPR-based modifications. Overall, this review shows the potential of microalgae in sustainable aquaculture, and provides an assessment of current developments and successes in CRISPR-based genome editing in microalgae as well as the potential future uses of its metabolic engineering and gene editing strategies.

Flocculation followed by gravity sedimentation is a low-cost method for microalgae harvesting. Cationic cellulose nanocrystals (CNCs) are novel flocculants composed of cellulose, a bio-based and abundantly available material. While CNCs yield good separation efficiencies for freshwater microalgae, they are less effective for marine microalgae because of the formation of small flocs with a poor settling rate. In this study, we evaluate whether dissolved air flotation (DAF) is a more effective separation method than gravity sedimentation for marine microalgae. The freshwater microalga Chlorella vulgaris formed bigger flocs (390 µm) than the marine microalga Nannochloropsis oculata (60 µm) and the smaller floc size resulted in a slower settling rate of the flocs and a lower maximum separation efficiency for N. oculata (71 %) compared to C. vulgaris (99 %). Transfer of C. vulgaris to a marine medium and N. oculata to a freshwater medium resulted in a decrease and increase in floc size respectively, as well as an increase and decrease in separation efficiency respectively. This demonstrated that differences in floc size between the marine and freshwater species are due to the differences in ionic strength of the culture medium and not the inherent properties of the two model species. When DAF was used to separate the flocs from the culture medium, the separation efficiency of C. vulgaris remained as high as when sedimentation was used, while the separation efficiency for N. oculata increased from 71 to 90 %. Simultaneously, the minimum dose of cationic CNCs required to induce flocculation in N. oculata decreased from 16 mg L⁻¹ to 3.2 mg L⁻¹. These results suggest that, for harvesting marine microalgae, flocculation is better combined with DAF rather than with gravity sedimentation. The better performance of DAF compared to sedimentation is ascribed to the fact that DAF is highly efficient in removing small flocs from suspension.

Microalgal biotechnology is a promising solution for bioremoval of nutrients, especially phosphorus (P). Microalgae can accumulate large quantities of P and the P-enriched algal biomass can be used as bio-fertilizer. Immobilization of microalgae on cheap, biocompatible, and biodegradable chitosan-based carriers facilitates the biomass harvesting, increases the stress resilience of their cells and improves the economic viability of the technology. Here, we demonstrated that immobilization of the green microalga Lobosphaera sp. IPPAS C-2047 on a chitosan-based carrier increased the bioremoval of P from the cultivation media. This effect was accompanied by the build-up of P-rich deposits in the cell wall and an expansion of the vacuolar compartment harboring the bulk P of the cell. An increase in the abundance of P-rich intracellular inclusions as compared to the cells of suspended culture was revealed by ultrastructure analysis and confirmed by energy-dispersive spectroscopy (EDS). The immobilization of the Lobosphaera sp. cells resulted in reorganization of their cell wall, increase in its electron density and thickness, probably due to the penetration of the chitosan nanoparticles into cells. This hypothesis was supported by the pattern of the changes in elemental composition of the Lobosphaera sp. cell wall which revealed, in addition to the anions (phosphate, nitrate, sulfate and chloride) adsorbed to the positively charged nanoparticles of chitosan, a characteristic presence of cationic counterions (potassium, sodium, magnesium, calcium). The presence of the putative chitosan particles was also noted in the vacuoles. Overall, the rearrangements in the cell of the Lobosphaera sp. triggered by its immobilization on chitosan seem to be among the factors increasing its cell quota for P accumulation and hence the removal efficiency for this nutrient as compared to the suspended cell.

To assess the future impact of climate change on the large brown seaweed Undaria pinnatifida, sporophyte growth was projected in the Sanriku coastal area on the Pacific coast of northeastern Japan, which is one of the main Undaria cultivation areas in the country. We first developed a growth model for Undaria sporophytes based on environmental conditions measured by mooring observations at an Undaria farm in the central part of the Sanriku coastal area. The growth model was run under the projected environmental conditions by climate models under Representative Concentration Pathway (RCP) scenarios to project sporophyte growth in the 2010s and the 2090s. The dates of start and end of cultivation in the growth model were determined as being when the nitrate concentration exceeded 20 µg L⁻¹ and decreased below 20 µg L⁻¹, respectively. The projected growth at the mooring observation indicated that, under several projected environmental conditions, there will be no significant difference in total length between the 2090s and the 2010s. However, in an alternative projection under RCP2.6 showed that the total length in the 2090s would be significantly longer than that in the 2010s. A significant change was projected in the delay of the start date and forward shift of the end date of cultivation under RCP8.5, suggesting that the cultivation schedule will change significantly from the current schedule. Projections of future Undaria growth throughout the Sanriku coastal area revealed that a significant decrease in total length will occur south of 39°N under RCP8.5.

Due to immobilization of heavy metals in the environment, it is necessary to evaluate their toxic effects on living cells. In this study, ecotoxicity of Cd and Cu was studied on inhibition of growth, chlorophyll a (Chl a) and chlorophyll b (Chl b), protein thiol groups and changes in bioconcentration factor (BCF). Cadmium toxicity was confirmed to be higher than Cu on Scenedesmus quadricauda. While in the lower concentrations of Cu the specific growth rate (SGR) was increased, in the presence of Cd only inhibition was confirmed. Level of Chl a was decreased more than level of Chl b. Only at low of Cu concentrations up to 0.07 mg L⁻¹ the specific growth rate and both photosynthetic pigments increased compared to control. We observed a high bioaccumulation of Cd and Cu in the cells through bioconcentration values. We determined a negative correlation between protein thiol groups and the Chl a (r=-0.461, p<0.01) and Chl b (r=-0.416, p<0.01), respectively, in Cu presence that indicates higher consumption of protein thiol groups probably due higher level of oxidative stress in the cells. Although, we did not confirm this significant correlation for cells cultivated in the presence of Cd, we found significant negative correlation between Cd accumulation and Chl a (r=-0.643) or Chl b (r=-0.699), respectively. S. quadricauda could be suitable candidate for bioremediation of contaminated waters (e.g. in algae-bacteria consortium) because has high capacity of Cd and Cu bioaccumulation and still have enough protein thiols to protect against damage of possible higher oxidative stress.

The tube-net method has emerged as the preferred technique for commercial farming of red seaweeds like Kappaphycus alvarezii in Brazil, India, Zanzibar and the Philippines for Gracilaria edulis and Gracilaria dura in India. The advantages of this technique include, efficient seeding and harvesting, ease of deployment in deep waters, circumvents drifting of biomass, and more stability in inclement weather and high currents. The present investigation is based on three different types of commercial high-density polyethylene (HDPE) tube nets namely net 1, net 2 and net 3. The highest value for Young’s module (2.40 ± 0.96 MPa) and the stress (1.74 ± 0.31 MPa) was recorded for net 1; while the highest value for elongation at break (90.52 ± 4.75%) and relative density (0.91 ± 0.09) was reported in net 2. The minimum sediment accumulation rate of 3369.35 ± 439.81 mg (100 g)⁻¹ of net was reported on day 10 under 0.5 L min⁻¹ flow rate in net 2. CFD analysis revealed a 1.2 times increase in sediment deposition at a lower flow rate (0.5 L min⁻¹) to that of a higher flow rate (5 L min⁻¹). The lowest value of chlorophyll (27.34 ± 17.75 mg g⁻¹) was recorded in net 2. Therefore, net 2 can act as a simple-to-implement biofouling management solution in the commercial farming of red seaweeds. Nevertheless, the results reported here are based on in-vitro experiments, which is the limitation of the current investigation. Further studies based on field cultivation experiments are desired to confirm the observations emanating from this research.

Carboxymethyl-kappa-carrageenans (CMKCs) were synthesized from kappa-carrageenan extracted from the red alga Kappaphycus striatus with different molar ratios of monochloroacetic acid (MCA) in the presence of sodium hydroxide. The structural and physicochemical characteristic of products were evaluated by FT-IR, ¹³C and ¹H NMR spectra, degree of substitution, molecular weight, zeta potential and biological activity. Degree of substitution of carboxymethyl group in kappa-carrageenan ranged from 0.24 to 1.12. FT-IR and ¹³C NMR spectra proved the substitution of carboxymethyl group in kappa-carrageenan disaccharide unit. Molecular weight of CMKCs increased slightly while their zeta potential was lower compared to the parent kappa-carrageenan. CMKCs exhibited a slight difference in the lowest hemagglutination concentrations on native human blood group types and showed an increase in antioxidant activity. The results indicate that carboxymethyl-kappa-carrageenan derivatives from kappa-carrageenan of the cultivated red alga K. striatus could be a good source of materials for application.

Chlorella and its metabolites have been known for decades to affect skin and beauty positively. With its increasing use in cosmeceuticals, there is a growing interest in elucidating its potential, particularly the bioactive compounds extracted from Chlorella biomass. Chlorella has numerous advantages as the key ingredient in cosmeceutical products as it can be easily cultivated, is highly adaptable in various environmental conditions, and contains high-value metabolites. The bioactive compounds include polysaccharides, chlorophyll, carotenoids, lutein, and peptides, demonstrating antioxidant, anti-aging, moisturizing, brightening, and UV-protection properties that are highly desirable in cosmeceutical products. This review highlights the biodiversity of Chlorella bioactive compounds, the application of Chlorella and its bioactive compounds for commercial cosmeceutical products, along with the production and extraction systems that have not been discussed elsewhere. Further optimization on the extraction and purification of bioactive compounds from microalgae biomass and the use of genetic engineering and omics of Chlorella will have the potential to improve the purity and yield of bioactive compounds.

A comparative study of the structural and physicochemical properties of commercial fucoidans produced by Sigma-Aldrich and fucoidans isolated by low-temperature extraction from the brown alga Fucus vesiculosus was performed. The structural features of fucoidans and their behavior in solutions and condensed phases (films) have been studied by various methods of physico-chemical analysis. It was shown that a water-soluble interpolymer complex was formed between fucoidan and alginate. The alginate/fucoidan complex was due to the formation of a cooperative system of hydrogen bonds between the ionogenic and hydroxyl groups of sodium alginate and fucoidan and hydrophobic interactions. The optimal conditions for the complex formation were realized at pH 6. The size of the complex particles was 0.5–1.7 nm. The film materials based on mixtures of fucoidan and sodium alginate were obtained. Using atomic force microscopy, it was shown that the morphology of the resulting alginate-fucoidan films was fine-grained, while the molecular weight of fucoidan did not affect the particle size of materials based on the alginate-fucoidan system. The particle sizes of the alginate/fucoidan interpolymer complex were significantly lower than those of the original polysaccharides. Testing of the microbiological activity of prepared alginate/fucoidan films against three Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa, and Proteus mirabilis and two Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis showed the pronounced inhibitory effect. The results obtained could be used for the production new materials in pharmaceutical and medical applications.

Biodiesel derived from cyanobacterial oils becomes attractive as an efficient renewable energy. The present study aims to optimize growth and lipid production of the halotolerant unicellular cyanobacterium Aphanothece halophytica cultivated in natural seawater. In this study A. halophytica was able to grow in natural seawater when supplemented with low concentration of NaNO3, whereas no growth occurred without supplementation. The specific growth rate of 0.230 day⁻¹ and cell concentration of 25.17 x 10⁶ cells mL⁻¹ were achieved in A. halophytica cultivated in natural seawater supplemented with 17.6 mM NaNO3 and Turk Island salt solution (suitable natural seawater; SNSW) for 14 days. This growth rate was comparable to that of cells grown in normal BG11 plus Turk Island salt solution. The lipid content and fatty acid profiles of A. halophytica varied with changes in NaCl concentrations. The highest lipid content of 50.47 % and lipid productivity of 48.33 mg L⁻¹ day⁻¹ were obtained in cultures supplemented with 1.89 mmol C-atom L⁻¹ glucose and 0.75 M NaCl. The optimal medium pH and cultivation temperature for lipid production was 7.5 and 25-35 °C, respectively. When cultivating A. halophytica in optimized SNSW with various NaCl concentrations, the highest contents of linoleic and linolenic acids, and the lowest contents of palmitic, stearic, and oleic acids were observed with 0.75 M NaCl. In contrast, cultures grown in optimized SNSW with 0.5 M NaCl showed fatty acid methyl ester profiles rich in monounsaturated fatty acids, which are favorable for high-quality biodiesel production.

As the world average temperature is on the rise and heat waves are becoming more prevalent, microalgal producers have been facing significant challenges regarding the time periods during which they are able to grow less thermotolerant microalgae in outdoor production facilities. Therefore, it is urgent to explore how microalgae cope with thermal stress and under which growth conditions tolerance to temperatures close to or higher than their maximum thermal threshold is induced. For this purpose, Tetraselmis striata CTP4, a euryhaline microalga known for its thermotolerance, was selected. Tetraselmis striata belongs to the Chlorodendrophyceae, a clade that branched off early from other "core chlorophyte" clades, usually comprised of microalgae able to colonise freshwater habitats. Here, we present compelling evidence that the ability of this microalga to withstand otherwise lethal thermal upshifts to 40 °C is induced by exposure to higher salinity (35 ppt). In contrast, this response is abrogated at lower salinities. Concomitantly, the expression of genes encoding HSP70 and HSP100, two heat shock proteins known to mediate thermotolerance and tolerance to other stresses (e.g., salt stress) in fungi, animals and plants, was enhanced when exposed to both heat stress and higher salinities. This suggests that cross-protective mechanisms against abiotic stress appeared early during the evolution of the core chlorophytes and of Archaeplastida in general. This knowledge can be used to select novel strains and growth conditions that promote thermotolerance in microalgae that are grown in outdoor industrial production facilities in environments where heat waves are expected.

Abundant low-grade Pyropia yezoensis and P. yezoensis waste are usually wasted due to poor taste. Pyropia polysaccharides are found in high amounts in low-grade P yezoensis and P. yezoensis waste and are a potential source of biodegradable film. This study evaluated the feasibility of using P. yezoensis polysaccharides to elaborate biobased composite edible biodegradable films blended with sodium alginate and optimized the preparation process of edible film. Film of 1:2 proportion of P. yezoensis polysaccharides and sodium alginate had better morphological and mechanical properties (elongation at break 22.89%, tensile strength 5.65 MPa, water vapor permeability 11.47 × 10⁻¹¹ g m⁻² s⁻¹ Pa⁻¹ and oxygen permeability 3.25 × 10⁻⁵ g m⁻² h⁻¹ atm⁻¹). The films exhibited good antioxidant and antibacterial activity. The degradation experiments indicated that the films could be efficiently degraded. Moreover, the film showed effective preservations on strawberry fruits within 7 days. Therefore, this paper brings a new perspective for the development of low-grade P. yezoensis and P. yezoensis waste to produce sustainable edible biodegradable films, which showed potential applications in active food packaging. Graphical Abstract

Conservation units are still unclear for the commercially important kelp Saccharina japonica. Previous analyses of population genetic structure have yielded inconsistent results regarding the number of clusters, especially in Japan. Thus, the genetic structure of S. japonica in Japan was studied using the mitochondrial nad3-16S rDNA region. We detected 88 haplotypes in 483 individuals collected from 46 localities. Unique haplotypes and one or a few shared haplotypes at a local scale were found in most localities. The observed genetic structure revealed cryptic invasions of S. japonica within Japan and the value of the nad3-16S rDNA region for identifying the geographic origin of kelp. Bayesian Analysis of Population Structure analysis and FST revealed the genetic divergence of populations in southwestern Hokkaido. The haplotype network showed a more detailed starburst pattern compared with the results of previous studies based on mitochondrial COI and trnW-trnI. Accordingly, S. japonica in Japan may represent one genetic group that experienced a recent expansion. Unique or locally shared haplotypes and similarity in haplotype diversity on different coasts of Hokkaido could be explained by refugia during the Last Glacial Maximum on various coasts. Furthermore, the present study demonstrated inconsistencies between the genetic structure and distribution of S. japonica varieties. Therefore, further investigations focused on the taxonomic validation of varieties are needed.

Conventional agriculture is highly dependent on chemical inputs and this leads to adverse environmental effects. Microalgae-based biofertilizers and biostimulants offer a promising solution to the challenges facing modern agriculture. In this work, two axenic microalgae strains were isolated from clay soil in the subtropical rainforest of Misiones, Argentina. These strains were identified as Chlorococcum vacuolatum CMI012 and Graesiella emersonii CMI015, and biomass production was characterised. The strains demonstrated differential effects as biostimulants for tomato germination and plant seedling growth under controlled conditions. Seed priming with C. vacuolatum supernatant improved germination and cotyledon emergence by 0.75 and 1.3-fold, respectively. Cellular extracts from the same strain at low concentration promoted cotyledon emergence by 1.3-fold. The effect of live microalgae cultures on tomato seedling growth was tested and G. emersonii CMI015 demonstrated significant biostimulation, enhancing root length and dry weight by nearly 100% and dry weight and height of the shoot by 50% and 20%, respectively. Both strains showed the ability to grow in 100 µg mL⁻¹ of four commonly used agrochemicals, indicating potential application in soil for the prevention of agrochemical runoff. This research emphasises the importance of isolating new microalgae from soil and evaluating their potential as biostimulants for their use in agriculture.

Kelp forests are likely to experience significant ramifications under future climate scenarios. A rise in sea surface temperature is likely to be the major climate-related effect on marine systems over the coming decades. Ribbon kelp (Alaria marginata) is a high latitude subcanopy species of commercial importance. In this study, 10 fertile specimens per location were collected from Juneau and Kodiak, Alaska. Spores produced by these individuals were cultivated for 30 days in four temperature treatments: 8°C, 11°C , 14°C, and 17°C. These produced gametophytes after approximately 15 days. Gametophytes grew to maximum size between 11-14°C, while 8°C resulted in smaller gametophytes but had no impact on reproductive development or the production of eggs and sporophytes. Production of eggs was observed after approximately 20 days, and production of sporophytes was observed after approximately 25 days. Temperatures between 11-14°C were optimal for the production of eggs, while 8°C was optimal for sporophyte production. The size of juvenile sporophytes after 30 days did not differ between temperatures up to 14°C. The 17°C treatment had significant adverse effects on spore germination, gametophyte development and reproduction. We observed a degree of population-level variation at all stages of the life cycle up to and including juvenile sporophytes. Specimens from Kodiak exhibited sporophyte production earlier than Juneau cultures, while Juneau cultures produced more sporophytes overall. Kodiak gametophytes grew larger between 11 - 14°C, but at 17 °C showed no sexual differentiation and did not produce eggs. Juneau gametophytes grown at 17 °C did produce eggs and were sexually differentiated up to the 20 day mark. These results provide specific hatchery conditions for the commercial cultivation of A. marginata and maximization of yield. Additionally, they provide insight into the resilience and persistence of populations under climate change conditions.

This study examined how inclusion of the diatom Amphora coffeaeformis in the diet affected Red Tilapia (Oreochromis niloticus × O. mossambicus) growth performance, body composition, metabolic parameters, gene expression, and resistance to Saprolegnia infection. Fish weighing an average of 9.0 ± 0.3 g were randomly stocked at a rate of 20 fish per pond (in triplicates), in four equal groups, and fed varied concentrations of A. coffeaeformis at 0% (Control), 1.5%, 3.0%, and 4.5% of diet for 56 days. After the eight-week trial, the fish were infected with Saprolegnia and the cumulative mortality was determined. Amphora coffeaeformis fed fish showed significant (P < 0.05) gains in growth and survival. Supplementation with A. coffeaeformis resulted in significant (P < 0.05) overexpression of genes including CAT, SOD, GPX, CCchemokine, IL1β, and IL8. Intestinal villi height and width were substantially increased (P < 0.05) in the A. coffeaeformis dietary fish groups compared to the control. When exposed to Saprolegnia, mortality was reduced in the A. coffeaeformis dietary fish groups. As a result, nutritional supplementation with A. coffeaeformis protected the fish from Saprolegnia infection. In conclusion, the current study indicates that dietary A. coffeaeformis improves red tilapia growth performance, hematological, biochemical, immunological response, and survival.