Metabolism balance regulation for squalene production by disturbing triglyceride (TAG) synthesis in Schizochytrium sp.

Abstract

Schizochytrium sp., a unicellular, eukaryotic heterotrophic marine microorganism, is rich in lipids that can serve as a potential cell factory for producing high-value compounds through the mevalonate (MVA) pathway, which competes with triglyceride (TAG) synthesis for precursors. In this study, TAG synthesis was disturbed to shift the precursors for squalene production by the MVA pathway, and the changes in cell metabolism of Schizochytrium limacinum SR21 were explored. Compared with the wild strain, the Δelo1 (elongase gene for fatty acid synthesis) and Δpap (phosphatidic acid phosphatase gene for triglyceride synthesis) strains provided more precursors for squalene synthesis, showing an increase of 35.6 % and 37.1 %, respectively. Considering the adverse effect of Δpap on TAG synthesis, the elo1 knockout and pap interference were regulated combinedly in the mutant strain (named the MIX strain) to improve squalene synthesis. The biomass and lipid contents of the MIX strain decreased by 13.6 % and 18.5 %, while the squalene titer increased by 41.4 %, reaching a value of 10.1 mg/L. The pap interference induced the flow of more glyceraldehyde 3-phosphate during pyruvate synthesis to produce more acetyl-coenzyme A (CoA). In contrast, the combined Δelo1 redistributed acetyl-CoA, promoting the production of adequate adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) by the tricarboxylic acid (TCA) cycle flux, and increased the flow of the precursors into the MVA pathway. This study provides a novel strategy for exploring lipid metabolism and lays a foundation for establishing cell factories for terpenoid synthesis by Schizochytrium sp.