Regulatory mechanism of ferrous ion in enhancing the biosynthesis of L-homoserine, L-threonine, and L-isoleucine in Corynebacterium glutamicum.

Abstract

Iron is a vital nutrient for almost all living organisms, predominantly existing in its ferrous Fe²⁺ and ferric Fe³⁺ states within cells. The limited bioavailability of Fe³⁺ due to its poor solubility necessitates Fe²⁺ supplementation in bacterial culture media to meet cellular demands. During fermentation studies with three Corynebacterium glutamicum strains, elevated Fe²⁺ concentrations were observed to enhance biomass accumulation, accelerate glucose consumption, maintain pH homeostasis, and promote product synthesis. To elucidate the precise transmission of iron signaling to amino acid biosynthetic pathways, transcriptomic analysis was performed on cultures grown under varying Fe²⁺ concentrations. Functional enrichment analysis of differentially expressed genes revealed that Fe²⁺ orchestrated a multifaceted regulatory response: upregulation of oxidative phosphorylation enhanced ATP production, downregulation of energetically costly siderophore transport systems optimized resource allocation, and induction of antioxidant defenses mitigated cell damage. This metabolic reprogramming resulted in significant yield improvements of 25.4% for L-homoserine, 20% for L-threonine, and 16.9% for L-isoleucine. The systematic characterization of these Fe²⁺-dependent regulatory networks provides novel metabolic engineering targets for industrial strain optimization.