Promotional mechanism of high glycerol productivity in the aerobic batch fermentation of Candida glycerinogenes after feeding several amino acids

摘要

To disclose the addition of some strong promotional amino acids (namely glycine, glutamate, lysine and aspartic acid) is how to improve the glycerol productivity of Candida glycerinogenes. An amino acid addition strategy based on dynamic enzyme activity was applied to improve glycerol productivity and decrease the byproducts formation in a fermentation of C. glycerinogenes in a 7-1 bioreactor. Compared with the control, after feeding glycine, glutamate, lysine and aspartic acid, glycerol productivity obtained an increase of 22.3, 25.6, 23.5 and 28.6%, respectively; meanwhile, the amounts of ethanol, acetic acid and pyruvate decreased largely. Whichever glycine, lysine, glutamate or aspartic acid was fed could elevate the activities of glucose-6-phosphate dehydrogenase (G6PDH), citrate synthase (CIT), triosephosphate isomerase (TPI) and cytoplasmic NAD+AEAAKw-dependent glycerol-3-phosphate dehydrogenase (ctGPD), and reduce the activities of pyruvate kinase (PYK), phosphofructokinase (PFK) and alcohol dehydrogenase (ADH). The reason of glycerol overproduction by the yeasts after feeding glycine, glutamate, lysine or aspartic acid is that the anaplerosis of intermediate metabolites in TCA cycle for amino acid degradation can decrease the flux from Embden-Meyerhof-Parnas (EMP) pathway to TCA cycle and enhance the flux through glycerol biosynthesis pathway. Above all, not only the high active hexose monophosphate (HMP) pathway but also the high dihydroxyacetone phosphate (DHAP) level plays an important role in the high glycerol productivity of C. glycerinogenes. The strategy of amino acid supplement is significant and can be economically implemented by an online process control strategy for higher yield of glycerol in industrial scale.