Nutrient deficiency induces a variety of cellular responses, including an increase in lipid accumulation in microalgae. Nitrogen starvation is the most studied deprivation. Here, we determine the effects of phosphorus and sulfur limitation on lipid accumulation in Chlorella vulgaris. A set of 9 experiments were performed, varying the initial concentration of these nutrients (set to 0, 50, and 100% of their original composition in Bold's basal medium). According to our results, the variation of P and S modified the specific growth rate, lag phase, and cell generation time. The ratio of 50%P and 0%S significantly increased the total lipid concentration. The fatty acid profile was dominated by C16:0, C18:0, and C18:1; a considerable increase in C20:5 was observed with 0%P and 50%S and 0%P and 100%S. Regarding neutral lipids, the response surface methodology (RSM) indicates that the maximum was observed when S was between 40 and 60% and P was between 95 and 100%. Therefore, the enhanced production of lipids caused by P and S limitation may contribute to the efficient oil production useful for algal biofuels.

• Klíčová slova
• Fatty acids, Lipids, Microalgae, Nutrient deficiency,
• MeSH
• biomasa MeSH
• biopaliva MeSH
• Chlorella vulgaris * metabolismus   MeSH
• dusík metabolismus   MeSH
• fosfor metabolismus   MeSH
• lipidy MeSH
• mastné kyseliny * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• biopaliva MeSH
• dusík MeSH
• fosfor MeSH
• lipidy MeSH
• mastné kyseliny * MeSH

BACKGROUND: Algae are prominent producers of carotenoids and polyunsaturated fatty acids which are greatly prized in the food and pharmaceutic industry. Fucoxanthin represents a notable high-value carotenoid produced exclusively by algae. Its benefits range far beyond just antioxidant activity and include cancer prevention, anti-diabetes, anti-obesity, and many other positive effects. Accordingly, large-scale microalgae cultivation to produce fucoxanthin and polyunsaturated fatty acids is still under intensive development in the commercial and academic sectors. Industrially exploitable strains are predominantly derived from marine species while comparable freshwater fucoxanthin producers have yet to be explored. RESULTS: In this study, we searched for freshwater fucoxanthin producers among photoautotrophic flagellates including members of the class Chrysophyceae. The initial screening turned our attention to the chrysophyte alga Hibberdia magna. We performed a comprehensive cultivation experiments using a temperature × light cross-gradient to assess the impact of these conditions on the target compounds productivity. Here we present the observations that H. magna simultaneously produces fucoxanthin (max. 1.2% dry biomass) and polyunsaturated fatty acids (max. ~ 9.9% dry biomass) and is accessible to routine cultivation in lab-scale conditions. The highest biomass yields were 3.73 g L-1 accompanied by maximal volumetric productivity of 0.54 g L-1 d-1 which are comparable values to marine microalgae fucoxanthin producers in phototrophic mode. H. magna demonstrated different optimal conditions for biomass, fucoxanthin, and fatty acid accumulation. While maximal fucoxanthin productivities were obtained in dim light and moderate temperatures (23 °C× 80 µmol m-2 s-1), the highest PUFA and overall biomass productivities were found in low temperature and high light (17-20 °C × 320-480 µmol m-2 s-1). Thus, a smart biotechnology setup should be designed to fully utilize H. magna biotechnological potential. CONCLUSIONS: Our research brings pioneer insight into the biotechnology potential of freshwater autotrophic flagellates and highlights their ability to produce high-value compounds. Freshwater fucoxanthin-producing species are of special importance as the use of sea-water-based media may increase cultivation costs and prohibits inland microalgae production.

• Klíčová slova
• Chrysophyceae, Fucoxanthin, Hibberdia magna, Light and temperature effect, Microalgae, Polyunsaturated fatty acids, Volumetric productivity,
• MeSH
• biomasa MeSH
• Chrysophyceae * MeSH
• karotenoidy MeSH
• mastné kyseliny MeSH
• mikrořasy * MeSH
• nenasycené mastné kyseliny MeSH
• xanthofyly MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• fucoxanthin MeSH Prohlížeč
• karotenoidy MeSH
• mastné kyseliny MeSH
• nenasycené mastné kyseliny MeSH
• xanthofyly MeSH

Green algae are fast-growing microorganisms that are considered promising for the production of starch and neutral lipids, and the chlorococcal green alga Parachlorella kessleri is a favorable model, as it can produce both starch and neutral lipids. P. kessleri commonly divides into more than two daughter cells by a specific mechanism-multiple fission. Here, we used synchronized cultures of the alga to study the effects of supra-optimal temperature. Synchronized cultures were grown at optimal (30 °C) and supra-optimal (40 °C) temperatures and incident light intensities of 110 and 500 μmol photons m-2 s-1. The time course of cell reproduction (DNA replication, cellular division), growth (total RNA, protein, cell dry matter, cell size), and synthesis of energy reserves (net starch, neutral lipid) was studied. At 40 °C, cell reproduction was arrested, but growth and accumulation of energy reserves continued; this led to the production of giant cells enriched in protein, starch, and neutral lipids. Furthermore, we examined whether the increased temperature could alleviate the effects of deuterated water on Parachlorella kessleri growth and division; results show that supra-optimal temperature can be used in algal biotechnology for the production of protein, (deuterated) starch, and neutral lipids.

• Klíčová slova
• Parachlorella kessleri, cell cycle, deuterated lipid, deuterated starch, deuterium, energy reserves, growth processes, microalgae, reproduction events, starch, supra-optimal temperature,
• MeSH
• biomasa MeSH
• buněčné dělení fyziologie   MeSH
• Chlorophyta růst a vývoj   MeSH
• lipidy MeSH
• metabolismus lipidů fyziologie   MeSH
• mikrořasy metabolismus   MeSH
• škrob metabolismus   MeSH
• teplota * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• lipidy MeSH
• škrob MeSH

Multiple fission is a cell cycle variation leading to the production of more than two daughter cells. Here, we used synchronized cultures of the chlorococcal green alga Parachlorella kessleri to study its growth and pattern of cell division under varying light intensities. The time courses of DNA replication, nuclear and cellular division, cell size, total RNA, protein content, dry matter and accumulation of starch were observed at incident light intensities of 110, 250 and 500 µmol photons m-2s-1. Furthermore, we studied the effect of deuterated water on Parachlorella kessleri growth and division, to mimic the effect of stress. We describe a novel multiple fission cell cycle pattern characterized by multiple rounds of DNA replication leading to cell polyploidization. Once completed, multiple nuclear divisions were performed with each of them, immediately followed by protoplast fission, terminated by the formation of daughter cells. The multiple fission cell cycle was represented by several consecutive doublings of growth parameters, each leading to the start of a reproductive sequence. The number of growth doublings increased with increasing light intensity and led to division into more daughter cells. This study establishes the baseline for cell cycle research at the molecular level as well as for potential biotechnological applications, particularly directed synthesis of (deuterated) starch and/or neutral lipids as carbon and energy reserves.

• Klíčová slova
• Parachlorella kessleri, cell cycle pattern, deuterated lipid, deuterated starch, deuterium, energy reserves, growth processes, light intensity, reproduction events,
• MeSH
• buněčné kultury * MeSH
• buněčný cyklus * MeSH
• Chlorophyta růst a vývoj   MeSH
• světlo * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

BACKGROUND: Algae have attracted attention as sustainable producers of lipid-containing biomass for food, animal feed, and for biofuels. Parachlorella kessleri, a unicellular green alga belonging to the class Trebouxiophyceae, achieves very high biomass, lipid, and starch productivity levels. However, further biotechnological exploitation has been hampered by a lack of genomic information. RESULTS: Here, we sequenced the whole genome and transcriptome, and analyzed the behavior of P. kessleri NIES-2152 under lipid production-inducing conditions. The assembly includes 13,057 protein-coding genes in a 62.5-Mbp nuclear genome. Under conditions of sulfur deprivation, lipid accumulation was correlated with the transcriptomic induction of enzymes involved in sulfur metabolism, triacylglycerol (TAG) synthesis, autophagy, and remodeling of light-harvesting complexes. CONCLUSIONS: Three-dimensional transmission electron microscopy (3D-TEM) revealed extensive alterations in cellular anatomy accompanying lipid hyperaccumulation. The present 3D-TEM results, together with transcriptomic data support the finding that upregulation of TAG synthesis and autophagy are potential key mediators of the hyperaccumulation of lipids under conditions of nutrient stress.

• Klíčová slova
• 3D-TEM, Genome, Green alga, Lipid body, Parachlorella kessleri, RNA-seq, Transcriptome, Whole-genome sequence,
• Publikační typ
• časopisecké články MeSH