초록
l-Methionine biosynthesis is through multilevel regulated and multibranched biosynthetic pathway (MRMBP). Because of the complex regulatory mechanism and the imbalanced metabolic flux between branched pathways, microbial production of l-methionine has not been commercialized. In this study, local metabolic response in MRMBP of l-methionine was investigated and various crucial genes in branched pathways were determined. In l-serine pathway, the crucial gene was serABC. In O-succinyl homoserine (OSH) pathway, which was the C4 backbone of l-methionine, metB and metL controlled the metabolic flux jointly. In l-cysteine pathway, the crucial gene cysEfbr could disturb the flux distribution of local network in l-methionine biosynthesis. However, no crucial gene for l-methionine production in 5-methyl tetrahydrofolate (CH3-THF) pathway was found. The relation between these pathways was also researched. l-Serine pathway, as the upstream pathway of l-cysteine and CH3-THF, played a crucial role in l-methionine biosynthesis. l-Cysteine pathway showed the strongest controlling force of the metabolic flux, and OSH pathway was second to l-cysteine pathway. In contrast, CH3-THF pathway was the weakest, which was probably the mainly limited steps at present and had great potential in further research. In addition, constructed W3110 IJAHFEBC/pA∗HAmL was able to produce 2.62 g/L l-methionine in flask. This study is instructive for l-methionine biosynthesis and provides a new research method of biosynthesizing other metabolic products in MRMBPs.