Construction and transcriptomic analysis of salinity-induced lipid-rich flocculent microalgae

The lack of cost-effective nutrient sources and harvesting methods is currently a major obstacle to the production of sustainable biofuels from microalgae. In this study, Chlorella pyrenoidosa was cultured with saline wastewater in a stirred photobioreactor, and lipid-rich flocculent microalgae particles were successfully constructed. As the influent salinity of the photobioreactor increased from 0% to 3%, the particle size and sedimentation rate of flocculent microalgae particles gradually increased, and the lipid accumulation of microalgae also increased gradually. Transcriptome analysis showed that the number of differentially expressed genes (DEGs) in microalgae increased as the salinity of wastewater increased from 1% to 3%, and the number of up-expressed genes was greater than that of down-expressed genes in microalgae at different salinity levels. The enrichment analysis of DEGs showed that the up-expressed genes under salt stress mainly involved in fatty acid biosynthesis and other metabolic processes, which initially revealed the mechanism of the lipid accumulation of microalgal particles in saline wastewater. In addition, the expression and functions of genes involved in lipid and EPS synthesis pathway in microalgae were analyzed, and the key genes involved in salinity affecting lipid and EPS synthesis in microalgae were preliminarily identified. The results could provide novel insight for genetic engineering to regulate the construction of lipid-rich flocculent microalgae particles.