Combinatorial Engineering of Escherichia coli for Enhancing Lipoic Acid Production

Lipoic acid (LA) is a sulfur-containing cofactor with significant antioxidant and metabolism-regulating functions, which is widely used in the pharmaceutical and nutraceutical industries. However, current microbial production of LA relies on exogenous octanoic acid and synthesizes the product in a protein-bound form, requiring a subsequent dissociation step to obtain free LA. In this study, we constructed an Escherichia coli strain capable of de novo synthesizing free LA by deleting the compensatory pathway gene lplA and introducing eflpA, a lipoamidase that hydrolyzes protein-bound LA. A high-efficiency LA synthase (sllipA) was subsequently screened from Serratia liquefaciens and optimized at the gene copy-number level, resulting in a 44% increase in LA production. Furthermore, by enhancing the carbon flux from acetyl-CoA to the precursor octanoic acid and improving the intracellular supply of the key cofactors S-adenosylmethionine (SAM) and [4Fe-4S] iron-sulfur clusters, the LA titer was further increased by 184%. Finally, under controlled microaerobic production conditions, the optimized strain achieved an LA titer of 138.32 mg/L, representing the highest level of microbial LA production reported to date.