(191am) Adaptive Evolution of Microalgae Schizochytrium Sp. Under High Salinity Stress to Alleviate Oxidative Damage and Improve Lipid Biosynthesis

Schizochytrium sp. possesses a powerful lipid accumulation machinery that can be induced under stress conditions. However, stress-based strategies not only reduce the growth rate, but also cause oxidative damage to the cells, which can eventually lower the lipid yield. In the present study, adaptive laboratory evolution (ALE) combined high salinity was performed to enhance the antioxidant system and lipid accumulation. The final strain ALE150, which was obtained after 150 days, showed a maximal cell dry weight (CDW) of 134.5g/L and lipid yield of 80.14g/L, representing a 32.7 and 53.31% increase over the starting strain, respectively. Moreover, ALE150 exhibited an overall higher total antioxidant capacity (T-AOC) and lower ROS levels than the starting strain. Furthermore, the regulatory mechanisms responsible for the improved performance of ALE150 were analyzed by comparative transcriptomic analysis. Genes related to the transhydrogenase cycle were upregulated while the pentose phosphate pathway (PPP) pathway was down-regulated. Moreover, the metabolic fluxes towards the fatty acid synthase (FAS) and polyketide synthase (PKS) pathways were also changed. Interestingly, an overall increase of gene expression levels of superoxide dismutase (SOD) and catalase (CAT) was essential for the survival of Schizochytrium sp. under 30 g/L salt.