Abstract: This work is to explore the effects of transaminase for L-alanine synthesis in Escherichia coli on the metabolism and L-tryptophan synthesis of the strain. Three genes（alaA,alaC and avtA）encoding L-alanine aminotransferase were knocked out by Red recombination technique. Fermentation experiments of shaking flask and 50 L fermenter were used to investigate the accumulation of L-tryptophan,L-alanine metabolism and cell growth. Results showed that the growth of the cells and L-tryptophan synthesis were strongly inhibited in these 3 genes deficient engineering strain E. coli FS-T0ΔalaAΔalaCΔavtA;however,the influences on the growth of single or both L-alanine aminotransferase-deficient strains were very little,but L-tryptophan synthesis varied significantly. By E. coli FS-T4ΔalaAΔalaC engineering strain,the yield of L-tryptophan was 6.08 g/L while the L-alanine production was only 0.16 g/L,which increased by 26.7% and decreased by 91.0%,respectively compared with the original strain. In the 50-L fermenter,the yield of L-tryptophan further increased to 41.9 g/L,and glucose conversion rate was 20.5%,which was 13.8% and 5.1% higher than the original strain,respectively. Deficiency of both AlaA and AlaC transaminase will not affect the needs of the whole cell amino acid pool,and is conducive to reduce the accumulation of miscellaneous acids,thus leading more carbon sources into L-tryptophan synthesis metabolic flux.

Key words: L-tryptophan, L-alanine, L-alanine aminotransferase