Conversion of methionine biosynthesis inE. colifrom trans- to direct-sulfurylation enhances extracellular methionine levels

Abstract

Methionine is an essential amino acid in mammals and a critical metabolite in all organisms. As such, various applications, including food, feed, and pharmaceuticals, necessitate the addition of L-methionine. Although amino acids and other metabolites are commonly produced through bacterial fermentation, high-yield biosynthesis of L-methionine remains a significant challenge due to the strict cellular regulation of the biosynthesis pathway. As a result, methionine is produced primarily synthetically, resulting in a racemic mixture of D,L-methionine. This study aimed to enhance methionine bio-production yields inE. coliby replacing its highly regulated trans-sulfurylation pathway with the more common direct-sulfurylation pathway used by other bacteria. To this end, we generated an auxotrophE. colistrain (MG1655) by simultaneously deletingmetAandmetBgenes and complementing them withmetXandmetYfrom different bacteria. Complementation of the genetically modifiedE. coliwithmetX/metYfromCyclobacterium marinumorDeinococcus geothermalis, together with the deletion of the global repressormetJand overexpression of the transporter YjeH, resulted in a substantial increase of up to 126 and 160-fold methionine relative to the wild-type strain, respectively, and accumulation of up to 700 mg/L using minimal MOPS medium and 2 ml culture. Our findings provide a method to study methionine biosynthesis and a chassis for enhancing L-methionine production by fermentation.