Metabolic Engineering of Aureobasidium melanogenum for Efficient Production of Gluconic Acid

Gluconic acid is an organic acid with extensive applications in food additives, pharmaceuticals, and chemical manufacturing. Recently, the integration of synthetic biology and microbial fermentation technologies has intensified interest in gluconic acid production. In this study, Aureobasidium melanogenum TSYW-58, isolated from natural environments and exhibiting an innate gluconic acid production capability, was employed as the starting chassis. Key genes responsible for the biosynthesis of pullulan, polymalic acid, liamocin, and melanin were deleted to reduce byproducts. Subsequently, overexpression of the endogenous glucose oxidase gene led to the creation of strain PPLMPG-6. Shake flask fermentation achieved a titer of up to 166.33 ± 8.08 g/L, while fed-batch fermentation in a 5 L bioreactor yielded 453.89 ± 16.50 g/L of gluconic acid, representing the highest production level reported to date. This work not only establishes a robust high-yield strain for industrial gluconic acid biosynthesis but also offers valuable insights for the microbial production of other organic acids.