Metabolic analysis of Schizochytrium sp. mutants with high EPA content achieved with ARTP mutagenesis screening

Eicosapentaenoic acid (EPA) belonged to the ω-3 series of polyunsaturated fatty acids and had physiological functions lipid as regulating blood lipid and preventing cardiovascular diseases. Schizochytrium sp. was considered to be a potential industrial fermentation strain of EPA because of its fast growth, high oil content, and simple fatty acid composition. However, Schizochytrium sp. produced EPA with low production efficiency and a long synthesis path. This research aims to improve the yield of EPA in Schizochytrium sp. by ARTP mutagenesis and to reveal the mechanism of high-yield EPA through transcriptome analysis. ARTP mutagenesis screening yielded the mutant M12 that whereas the productivity of EPA increased 108% reaching 0.48 g/L, the total fatty acid concentration was 13.82 g/L with an increase of 13.7%. The transcriptomics revealed 2995 differentially expressed genes were identified between M12 and the wild-type strain and transcripts involved in carbohydrate, amino acid, energy, and lipid metabolism were up-regulated. Among them, the hexokinase (HK) and the phosphofructokinase genes (PFK), which can catalyze pyruvate to acetyl-CoA, were increased 2.23-fold and 1.78-fold. Glucose-6-phosphate dehydrogenase (G6PD) and glutamate dehydrogenase (GLDH), which can both generate NADPH, were increased by 1.67-fold and 3.11-fold. Furthermore, in the EPA synthesis module, the expression of 3-oxoacyl-[acyl-carrier protein] reductase(fabG) and carbonyl reductase 4 / 3-oxoacyl-[acyl-carrier protein] reductase beta subunit(CBR4), also up-regulated 1.11-fold and 2.67-fold. These may lead to increases in cell growth. The results provide an important reference for further research on promoting fatty acid and EPA accumulation in Schizochytrium sp.