Enhancing l-Malic Acid Production in via Natural Activation of Gene Expression.

The efficient production of l-malic acid using requires overcoming challenges in synthesis efficiency and excessive byproduct buildup. This study addresses these hurdles, improving the activity of NADH-dependent malate dehydrogenase (Mdh) in the early stages of the fermentation process. By employing a constitutive promoter to express the responsible for the transfer of reducing equivalents between NAD(H) and NADP(H) in , the l-malic acid production was significantly elevated. However, this resulted in conidiation defects of , limiting industrial viability. To mitigate this, we discovered and utilized the PmfsA promoter, enabling the specific expression of during the fermentation stage. This conditional expression strain showed similar phenotypes to its parent strain while exhibiting exceptional performance in a 5 L fermenter. Notably, it achieved a 65.5% increase in productivity, reduced fermentation cycle by 1.5 days, and lowered succinic acid by 76.2%. This work marks a promising advancement in industrial l-malic acid synthesis via biological fermentation, showcasing the potential of synthetic biology in for broader applications.