[Multi-strategy modification for constructing an engineered strain with efficient production of O-acetyl-...

O-acetyl- l- homoserine (OAH) is a key intermediate in the synthesis of various high-value compounds such as l-methionine and has a high market value. However, the production of OAH still faces problems such as low yields and long fermentation periods. In this study, the wild type of the probiotic Escherichia coli Nissle 1917 (EcN) was used as the starting strain. Firstly, we obtained the mutant MetX^{K185R-G210S-N204T} by modifying the key enzyme l-homoserine acetyltransferase (MetX). Further, ppc, asd, and metL were overexpressed to strengthen the synthetic pathways of the precursors l-aspartic acid and l-homoserine. Strategies such as dynamic regulation were adopted to weaken the synthesis of the by-product amino acids. Different intensities of 5{L-End} ' UTR were screened to downregulate the expression level of gltA to balance the supply of another precursor acetyl-CoA, and finally an efficient OAH-producing strain was constructed. The fermentation yield of OAH in the shake flask was 11.18 g/L, and that in the 5 L fermenter reached 63.54 g/L at the time point of 52 h. The strain engineering improved the yield and productivity of OAH and laid a research foundation for the subsequent biological production of l-methionine.