Abstract: O-acetyl-homoserine（OAH）is an important industrial ingredient for homoserine and methionine production. We used the modified threonine-producing strain Escherichia coli ThrL as the host strain,to overexpress homoserine dehydrogenase gene thrA and homoserine acetyltransferase gene metX that are key genes for OAH production. The promoter combination was designed to optimize the transcription of these two key genes. Then,the concentrations of threonine and yeast extract in the fermentation medium were also optimized. After the promoter combination optimization,it showed that the OAH yield of the recombinant strain E.coli OAH4,in which the thrA and metX genes were separately controlled by J23110 promoter,was the highest and reached up to 1.54 g/L after 50 h incubation. When the concentrations of threonine and yeast extract were 2 g/L and 6 g/L,respectively,the OAH yield of E. coli OAH4 was the highest and further increased to 1.98 g/L after 50 h incubation. In this study,the synthesis of OAH was achieved in E. coli for the first time. The expression of thrA and metX,and fermentation conditions of OAH were optimized,which paved the way for the further OAH production research.

Key words: Escherichia coli, O-acetyl-homoserine, aspartate kinase I/homoserine dehydrogenase I, homoserine acetyltransferase, fermentation medium optimization