Systemic intracellular analysis for balancing complex biosynthesis in a transcriptionally deregulated Escherichia coli l‐Methionine producer

Abstract

Abstract l‐Methionine (l‐Met) has gained remarkable interest due to its multifaceted and versatile applications in the fields of nutrition, pharmaceuticals and clinical practice. In this study, the fluxes of the challenging l‐Met biosynthesis in the producer strain Escherichia coli (E. coli) DM2853 were fine‐tuned to enable improved l‐Met production. The potential bottlenecks identified in sulfur assimilation and l‐Met synthesis downstream of O‐succinyl‐l‐homoserine (OSHS) were addressed by overexpressing glutaredoxin 1 (grxA), thiosulfate sulfurtransferase (pspE) and O‐succinylhomoserine lyase (metB). Although deemed as a straightforward target for improving glucose‐to‐Met conversion, the yields remained at approximately 12%–13% (g/g). Instead, intracellular l‐Met pools increased by up to four‐fold with accelerated kinetics. Overexpression of the Met exporter ygaZH may serve as a proper valve for releasing the rising internal Met pressure. Interestingly, the export kinetics revealed maximum saturated export rates already at low growth rates. This scenario is particularly advantageous for large‐scale fermentation when product formation is ideally uncoupled from biomass formation to achieve maximum performance within the technical limits of large‐scale bioreactors.