Abstract: L-Trp is an essential amino acid, which is widely used in food supplement, medicine and feed-stocks. Annual demand in the world is more than 10,000 tons, but the actual capacity all over the world is only 3000 tons, which is far from satisfying the needs of market. In China, there is only small-scale production of L-Trp in Wuhan, Shanghai and Beijing, about 100 tons a year. This makes the application of L-Trp limit in the medicine. In this paper, we used a recombinant E.coli strain to develop a mode of glucose-feeding to enhance the production of L-Trp to a certain level
Firstly, we studied the impact of glucose, NH4+ and PO43-concentrations on cell growth and L-Trp production. Result shows that, under the condition of high glucose concentration, the broth accumulates a lot of Acetic acid, which made cell and L-Trp concentration is low. 50mM NH4+ and 7.5g/L~15g/L PO43- made the fermentation process have the highest yield of L-Trp. At the same time we could see that NH4+ concentration have a stronger impact on the L-Trp production than PO43-.
In the fermentor, we performed glucose-fed batch fermentation. Glucose fed mode includes the index fed of µset=0.10, 0.15, 0.20and pulse fed mode according to the experience. The final output of L-Trp is between 8g/L~11g/L, lower than data reported by others. The main reason for the low output is that the fermentation process accumulates excessive acetic acid and there is no production in the stability period. Therefore, to reduce the acetic acid accumulation and to allow E. coli produce L-Trp in the stable period has become the focus of future study. The time when the acetic acid began to accumulate generally is the time when bacteria has fastest growth rate. Therefore, it is necessary to reduce the fed rate of glucose, especially near the period of stability.
Key words：L-Tryptophan; recombinant Escherichia coli; fermentation; glucose index fed
