(29n) Carbon-Economic Biosynthesis of Polymalic Acid and Malic Acid from Ethanol and Biomass Feedstocks

Polymalic acid (PMA) is a novel biopolymer composed of the monomer L-malic acid (MA), which has potential application in biomedical and environmental fields. Compared with sugars, the non-fermentable substrate ethanol exhibits a higher degree of reduction per carbon atom and a shorter route to generate acetyl-CoA. In this study, the carbon-economic biosynthesis of PMA driven by ethanol and biomass feedstocks was investigated. Ethanol was first found to be converted into PMA, and specially activated the transcription factor Cat8 to regulate the glyoxylic acid shunt in A. pullulans. A modular assembly strategy was designed to balance three modules of ethanol oxidation, glyoxylic acid shunt and the gluconeogenesis pathway. As a result, a mutant strain EGG47 was obtained and achieved a comparable PMA titer and yield of ~66.7 g/L and 0.87 g/g ethanol, Moreover, xylose-containing mother liquor was evaluated the feasibility for efficient PMA fermentation under low pH control and L-MA recovery in a non-waste-disposal system. The results showed that l-MA could recovery from the acidic downstream process without solid waste CaSO4. Our findings provide new insights into carbon-economic transformation form ethanol or the biomass feedstocks in third-generation biorefineries.