Abstract
β-poly (L-malic acid) (PMLA) is a biopolyester which has attracted industrial interest for its potential application in medicine and other industries. A high dissolved oxygen concentration (DO) was beneficial for PMLA production, while the mechanisms of DO in PMLA biosynthesis by Aureobasidium pullulans are still poorly understood. In this work, the amount of PMLA was first compared when A. pullulans ipe-1 were cultured under a high DO level (70% saturation) and a low DO level (10% saturation). Meanwhile, the key enzymes involved in different pathways of the precursor L-malic acid biosynthesis were studied. The results revealed that the activities of glucose-6-phosphate dehydrogenase (G6PDH) and phosphoenolpyruvate carboxylase (PEPC) were positively correlated with cell growth and PMLA production, while the activities of phosphofructokinases (PFK), pyruvic carboxylase (PC) and citrate synthetase (CS) did no show such correlations. It indicated that the Pentose Phosphate Pathway (PPP) may play a vital role in cell growth and PMLA biosynthesis. Moreover, the precursor L-malic acid for PMLA biosynthesis was mainly biosynthesized through phosphoenolpyruvic acid (PEP) via oxaloacetate catalyzed by PEPC. It was also found that low concentration of sodium fluoride (NaF) might impel carbon flux flow to the oxaloacetate through PEP, but inhibit the flux to the oxaloacetate via pyruvic acid.