The effect of NaCl stress on photosynthetic efficiency and lipid production in freshwater microalga-Scenedesmus obliquus XJ002.

Rapid industrialization and population growth have increased the world's energy demands, resulting in a shortage of conventional fossil fuels. Thus, there is an urgent need to develop sustainable and renewable forms of energy. Microalgae have emerged as a potential feedstock for biofuel production. Under stress conditions, lipid production is enhanced in algal cells due to changes in the lipid biosynthetic pathways that produce neutral lipids. In this study, we examined the physiological and biochemical effects of salinity stress (0.00, 0.01, 0.10, 0.15, 0.20M) on the freshwater microalga Scenedesmus obliquus XJ002. We found that the biomass and the content of chlorophyll a, b and carotenoids decreased with increasing NaCl concentration. NaCl stress damaged the oxygen evolving complex (OEC) and the PSII (photosystem II) reaction center and subsequently suppressed electron transport at the donor and receptor sides of the reaction center, influencing the absorption, transfer, and application of light energy. Additionally, the total lipid content of cells was significantly increased under NaCl stress treatment. The highest lipid content (32.26%) was found in cells cultured in the presence of 0.20M NaCl, which was about 2.52-fold higher than that of cells grown in medium lacking NaCl (12.82%). In addition to providing insight into the physiological and biochemical responses of S. obliquus XJ002 to salinity stress, these findings show that lipid production, and hence biofuel feedstock production, can be boosted by adjusting salt levels in the growth medium.