Combinatorial Engineering of <i>Escherichia coli</i> 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 <i>Escherichia coli</i> strain capable of <i>de novo</i> synthesizing free LA by deleting the compensatory pathway gene <i>lplA</i> and introducing <i>eflpA</i>, a lipoamidase that hydrolyzes protein-bound LA. A high-efficiency LA synthase (<i>sllipA</i>) was subsequently screened from <i>Serratia liquefaciens</i> 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.