Responses in growth, lipid accumulation,and fatty acid composition of four oleaginous microalgae to different nitrogen sources and concentrations

Nitrogen deficiency is an effective strategy for enhancing lipid production in microalgae. Close relationships exist among lipid production, microalgal species, and nitrogen sources. We report growth, lipid accumulation, and fatty acid composition in four microalgae （Chloroeoccum ellipsoideum UTEX972, Chlorococcum nivale LB2225, Chlorococcum tatrense UTEX2227, and Scenedesmus deserticola JNU19） under nitrate- and urea-nitrogen deficiencies. We found three patterns of response to nitrogen deficiency： Type-A （decrease in biomass and increase in lipid content）, Type-B （reduction in both biomass and lipid content）, and Type-C （enhancement of both biomass and lipid content）. Type-C microalgae are potential candidates for large-scale oil production. Chlorococcum ellipsoideum, for example, exhibited a neutral lipid production of up to 239.6 mg/（L＇d） under urea-nitrogen deficiency. In addition, nitrogen deficiency showed only a slight influence on lipid fractions and fatty acid composition. Our study provides useful information for further screening hyper-lipid microalgal strains for biofuel production.

Metabolic engineering and genome editing strategies for enhanced lipid production in microalgae

Depleting global petroleum reserves and skyrocketing prices coupled with succinct supply have been a grave concern,which needs alternative sources to conventional fuels.Oleaginous microalgae have been explored for enhanced lipid production,leading towards biodiesel production.These microalgae have short life cycles,require less labor,and space,and are easy to scale up.Triacylglycerol,the primary source of lipids needed to produce biodiesel,is accumulated by most microalgae.The article focuses on different types of oleaginous microalgae,which can be used as a feedstock to produce biodiesel.Lipid biosynthesis in microalgae occurs through fatty acid synthesis and TAG synthesis approaches.In-depth discussions are held regarding other efficient methods for enhancing fatty acid and TAG synthesis,regulating TAG biosynthesis bypass methods,blocking competing pathways,multigene approach,and genome editing.The most potential targets for gene transformation are hypothesized to be a malic enzyme and diacylglycerol acyltransferase while lowering phosphoenolpyruvate carboxylase activity is reported to be advantageous for lipid synthesis.

Genome-wide adenine N6-methylation map reveals epigenomic regulation of lipid accumulation in Nannochloropsis

Epigenetic marks on histones and DNA,such as DNA methylation at N6-adenine(6mA),play crucial roles in gene expression and genome maintenance,but their deposition and function in microalgae remain largely uncharacterized.Here,we report a genome-wide 6mA map for the model industrial oleaginous microalga Nannochloropsis oceanica produced by single-molecule real-time sequencing.Found in 0.1%of adenines,6mA sites are mostly enriched at the AGGYV motif,more abundant in transposons and 30 untranslated re-gions,and associated with active transcription.Moreover,6mA gradually increases in abundance along the direction of gene transcription and shows special positional enrichment near splicing donor and transcrip-tion termination sites.Highly expressed genes tend to show greater 6mA abundance in the gene body than do poorly expressed genes,indicating a positive interaction between 6mA and general transcription fac-tors.Furthermore,knockout of the putative 6mA methylase NO08G00280 by genome editing leads to changes in methylation patterns that are correlated with changes in the expression of molybdenum cofactor,sulfate transporter,glycosyl transferase,and lipase genes that underlie reductions in biomass and oil productivity.By contrast,knockout of the candidate demethylase NO06G02500 results in increased 6mA levels and reduced growth.Unraveling the epigenomic players and their roles in biomass productivity and lipid metabolism lays a foundation for epigenetic engineering of industrial microalgae.