Identification of gene transcripts involved in lipid biosynthesis in Chlamydomonas reinhardtii under nitrogen, iron and sulfur deprivation

Effects of sulfur and phosphorus concentration on the lipid accumulation and fatty acid profile in Chlorella vulgaris (Chlorophyta)

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.

Physiological and Genetic Regulation for High Lipid Accumulation by Chlorella sorokiniana Strains from Different Environments of an Arctic Glacier, Desert, and Temperate Lake under Nitrogen Deprivation Conditions

Microalgae can adapt to extreme environments with specialized metabolic mechanisms. Here, we report comparative physiological and genetic regulation analyses of Chlorella sorokiniana from different environmental regions of an arctic glacier, desert, and temperate native lake in response to N deprivation, for screening the optimal strain with high lipid accumulation. Strains from the three regions showed different growth and biochemical compositions under N deprivation. The arctic glacier and desert strains produced higher soluble sugar content than strains from the native lake. The arctic glacier strains produced the highest levels of lipid content and neutral lipids under N deprivation compared with strains from desert and native lake. At a molecular level, the arctic strain produced more differentially expressed genes related to fatty acid biosynthesis, glycolysis gluconeogenesis, and glycerolipid metabolism. The important functional genes acetyl coenzyme A (acetyl-CoA) carboxylase (ACCase), fatty acid synthase complex, pyruvate dehydrogenase component, and fatty acyl-acyl carrier protein (acyl-ACP) thioesterase were highly expressed in arctic strains. More acetyl-CoA was produced from glycolysis gluconeogenesis and glycerolipid metabolism, which then produced more fatty acid with the catalytic function of ACCase and acyl-ACP thioesterase in fatty acid biosynthesis. Our results indicated that the C. sorokiniana strains from the arctic region had the fullest potential for biodiesel production due to special genetic regulation related to fatty acid synthesis, glycolysis gluconeogenesis, and glycerolipid metabolism. IMPORTANCE It is important to reveal the physiological and genetic regulation mechanisms of microalgae for screening potential strains with high lipid production. Our results showed that Chlorella sorokiniana strains from arctic glacier, desert, and temperate native lake had different growth, biochemical composition, and genetic expression under N deprivation. The strains from an arctic glacier produced the highest lipid content (including neutral lipid), which was related to the genetic regulation of fatty acid biosynthesis, glycolysis gluconeogenesis, and glycerolipid metabolism. The functional genes for acetyl-CoA carboxylase, fatty acid synthase complex, pyruvate dehydrogenase component, and fatty acyl-ACP thioesterase in the three pathways were highly expressed in arctic strains. The revelation of physiological and genetic regulation of strains from different environmental regions will contribute to the microalgae selection for high lipid accumulation.

MicroRNA Expression Profile Analysis of Chlamydomonas reinhardtii during Lipid Accumulation Process under Nitrogen Deprivation Stresses

Lipid accumulation in various microalgae has been found induced by nitrogen deprivation, and it controls many different genes expression. Yet, the underlying molecular mechanisms still remain largely unknown. MicroRNA (miRNAs) play a critical role in post-transcriptional gene regulation. In this study, miRNAs were hypothesized involved in lipid accumulation by nitrogen deprivation. A deep-sequencing platform was used to explore miRNAs-mediated responses induced by nitrogen deprivation in Chlamydomonas reinhardtii. The eukaryotic orthologous groups of proteins (KOG) function in the predicted target genes of miRNA with response to nitrogen deprivation were mainly involved in signal transduction mechanisms, including transcription, lipid transport, and metabolism. A total of 109 miRNA were predicted, including 79 known miRNA and 30 novel miRNA. A total of 29 miRNAs showed significantly differential expressions after nitrogen deprivation, and most of them were upregulated. A total of 10 miRNAs and their targeting genes might involve in lipid transport and metabolism biological process. This study first investigates nitrogen deprivation-regulated miRNAs in microalgae and broadens perspectives on miRNAs importance in microalgae lipid accumulation via nitrogen deprivation. This study provides theoretical guidance for the application of microalgae in bio-oil engineering production.

The Geomagnetic Field (GMF) Modulates Nutrient Status and Lipid Metabolism during Arabidopsis thaliana Plant Development

The Geomagnetic field (GMF) is a typical component of our planet. Plant perception of the GMF implies that any magnetic field (MF) variation would induce possible metabolic changes. In this work was we assessed the role of the GMF on Arabidopsis thaliana Col0 mineral nutrition and lipid metabolism during plant development. We reduced the local GMF (about 40 μT) to Near Null Magnetic Field (NNMF, about 30 nT) to evaluate the effects of GMF on Arabidopsis in a time-course (from rosette to seed-set) experiment by studying the lipid content (fatty acids, FA; and surface alkanes, SA) and mineral nutrients. The expression of selected genes involved in lipid metabolism was assessed by Real-Time PCR (qPCR). A progressive increase of SA with carbon numbers between 21 and 28 was found in plants exposed to NNMF from bolting to flowering developmental stages, whereas the content of some FA significantly (p < 0.05) increased in rosette, bolting and seed-set developmental stages. Variations in SA composition were correlated to the differential expression of several Arabidopsis 3-ketoacyl-CoAsynthase (KCS) genes, including KCS1, KCS5, KCS6, KCS8, and KCS12, a lipid transfer protein (LTPG1) and a lipase (LIP1). Ionomic analysis showed a significant variation in some micronutrients (Fe, Co, Mn and Ni) and macronutrients (Mg, K and Ca) during plant development of plants exposed to NNMF. The results of this work show that A. thaliana responds to variations of the GMF which are perceived as is typical of abiotic stress responses.

pH effects on the lipid and fatty acids accumulation in Chlamydomonas reinhardtii

pH variations influence the delivery of essential nutrients and CO₂ solubility, which impact algae metabolism. In this study the microalgal growth and chlorophyll, lipid, and fatty acids content; along with the expression of some genes implicated in the biosynthesis of lipids were examined in Chlamydomonas reinhardtii subjected to pH values of 7.0, 7.8, and 8.5. At pH 7.8 an increase in cell growth was observed with a significant accumulation of chlorophyll (1.75-fold) when compared with growth at pH 7, while at pH 8.5 a sharp decrease in both parameters was observed when compared with the other pH values tested. Lipid content increased 3.0 (14.81% of dry cell weight, dcw) and 2.3 times (11.43% dcw) at pH 7.8 and 8.5, respectively, when compared with the experiment at pH 7 (4.97% dcw). The compositions of major fatty acids in the strains growing at pH 7.0, 7.8, or 8.5 were 25.7, 28.0, and 32.1% for palmitic acid; 17.3, 14.7, and 25.7% for oleic acid; and 9.8, 12.1, and 4.6% for linoleic acid; respectively. qRT-PCR analysis showed that the transcripts of ß-carboxyltransferase, Acyl carrier protein 1, acyl-ACP thiolase 1, acyl-sn-glycerol-3-phosphate acyltransferase, and diacylglycerol acyl transferase isoform 3 were significantly induced at pH 7.8 when compared with the other two pH conditions. These results indicate that the induction of genes implicated in the early and final steps of lipid biosynthesis contributes to their accumulation in the stationary phase. Our research suggests that a pH of 7.8 might be ideal to maximize growth and lipid accumulation.