(489e) Metabolic Engineering of Aureobasidium Pullulans for Enhanced Polymalic Acid Production through Enhancing Oxaloacetate Conversion, Malate Transportation, and PMA Synthesis

Polymalic acid (PMA) is a biopolymer with high water solubility, biocompatibility, and biodegradability. Its unique properties attract increasing attention in food and biomedical fields. Recently, many strains of Aureobasidium pullulans, the black yeast belonging to the order Dothideales of family Dothideaceae, capable of producing PMA as an extracellular polymer have been isolated. However, industrial production of PMA requires further improvements in fermentation performance, including product yield, titer, and productivity, through strain engineering and process optimization. The biosynthesis of malic acid (MA) which is the precursor of PMA in A. pullulans involves three pathways: the oxidative TCA cycle; the reductive TCA (rTCA) pathway where pyruvate carboxylase (PYC) converts pyruvate to oxaloacetate (OAA) and malate dehydrogenase (MDH) then converts OAA to malate; and the glyoxylate pathway after which the malate was transported by C4-dicarboxylate transporter (DAT). A hypothetical biosynthesis step from malate to PMA is that malate is transferred into malyl-CoA as intermediate and then synthesized by PMA synthase (PMS).

In this study, a PMA producing strain A. pullulans ZX-10 previously isolated in our lab was engineered to overexpress the malate dehydrogenase (MDH), the C4-dicarboxylate transporter (DAT) and PMA synthase (PMS) to increase PMA production. The effects of overexpressing these genes on cell growth and PMA production were studied in batch fermentation and the results are reported in this paper.