Investigation of poly(β-malic acid)synthesis pathways and regulation by strains of Aureobasidium pulluans

The possible biosynthesis pathways of poly(β-malic acid)(PMLA) and the feasible approaches to regulating PMLA production in A. pullulans BS24 were studied. To investigate the effects of the metabolic inhibitors of tricarboxylic acid cycle(TCA) cycle on PMLA fermentation, supplementation of the inhibitors to the medium was implemented. The results demonstrated that trifluoroacetic acid inhibited PMLA production, but malonic acid and maleic acid promoted PMLA production and isocitrate lyase activity. It could be concluded that PMLA synthesis was related to the TCA cycle and glyoxylate pathway in A. pullulans. Based on this result, the method of facilitating the accumulation of PMLA via metabolic intermediates was further designed. The medium containing 3.0 g·L^-1 fumaric acid or 1.5 g·L^-1 L-malic acid was used. Isocitrate lyase activity was increased by 18.39% and 25.30%, respectively. And the two added intermediates also increased the activity of L-malate dehydrogenase and fumarase, while reduced the activity of isocitrate dehydrogenase and α-ketoglutaric acid dehydrogenanse, and the final PMLA yield was increased by 46.58% and 43.70%, respectively. The metabolic intermediates could modify the redistribution of metabolic flux between TCA cycle and glyoxylate pathway, therefore, carbon source could be efficiently used to synthesize PMLA.