Abstract: L-tryptophanine（L-Trp）is a kind of restricted amino acid, which is one of the essential amino acids for the growth and development of human body and animal. It is one of the key amino acids in the synthesis of many active substances and has been widely used in medicine. The production of L- tryptophan by microbial fermentation has attracted much attention in recent years, mainly because of its low price, high purity and easy separation. Therefore, the production of L-tryptophan by microorganism has a promising application prospect in large-scale industrial production. In this paper, the tryptophan high yield gene was recombined into Escherichia coli by genetic engineering. By controlling dissolved oxygen, pH value of carbon source and residual sugar content, the yield of L-tryptophan was effectively increased by direct fermentation. In this experiment, the original strain was used to explore the content of residual sugar in fermenting tank. It was found that when the residual sugar content was controlled at 1%, the growth of bacteria was the best and the growth cycle was the longest. When molasses were mixed with glucose as carbon source during fermentation, the results showed that the yield of L-tryptophan was the highest when the ratio was 3:1; then when the pH was controlled during fermentation, the yield was increased to 18.9 g/L;the dissolved oxygen condition was controlled in the range of 35% and 40%. The results showed that the production of L-tryptophan reached 27 g/L at dissolved oxygen 40%; Finally, 60% glucose and 70% wheat sugar were replaced by carbon source. The results showed that the yield of L-tryptophan was higher when glucose was the sole carbon source.

Key words: L-tryptophan, fermentation, optimization, high yield strain