Abstract
The implementation of a novel cell recycling technology based on a special disk centrifuge during microbial fermentation process can continuously separate the product and harmful intermediates, while maintaining the cell viability owing to the installed cooling system. Acetate accumulation is an often encountered problem in L-tryptophan fermentation by Escherichia coli. To extend our previous studies, the current study deleted the key genes underlying acetate biosynthesis to improve l-tryptophan production. The deletion of the phosphotransacetylase (pta)–acetate kinase (ackA) pathway in a gltB (encoding glutamate synthase) mutant of E. coli TRTHB, led to the highest production of l-tryptophan (47.18 g/L) and glucose conversion rate (17.83%), with a marked reduction in acetate accumulation (1.22 g/L). This strain, TRTHBPA, was then used to investigate the effects of the cell recycling process on L-tryptophan fermentation. Four different strategies were developed concerning two issues, the volume ratio of the concentrated cell solution and clear solution and the cell recycling period. With strategy I (concentrated cell solution: clear solution, 1: 1; cell recycling within 24–30 h), L-tryptophan production and the glucose conversion rate increased to 55.12 g/L and 19.75%, respectively, 17.55% and 10.77% higher than those without the cell recycling. In addition, the biomass increased by 13.52% and the fermentation period was shortened from 40 h to 32 h. These results indicated that the cell recycling technology significantly improved L-tryptophan production by E. coli.
Highlights
Metabolic engineering is the purposeful modification of cellular activities aimed at improving the yield of a desired product through genetic engineering techniques [1]
We previously studied the effect of gene modification of the glutamate synthesis pathway on L-tryptophan production and selected an Escherichia coli strain with mutated gltB, designated as TRTHB, which was derived from the strain TRTH in our laboratory [2]
Characteristics trpEDCBA+TetR, ΔtnaA, ΔgltB Derived from TRTHB, but Δpta and ΔackA Derived from TRTHB, but Δpta and ΔtdcD Derived from TRTHB, but ΔpoxB Derived from TRTHBPA, but ΔpoxB
Summary
Metabolic engineering is the purposeful modification of cellular activities aimed at improving the yield of a desired product through genetic engineering techniques [1]. Gene modification in Escherichia coli for L-tryptophan production pharmaceutical industry, and it is the subject of intensive research [2, 3]. Glutamate formation is a major obstacle in tryptophan production. Reduction in glutamate formation has been demonstrated to increase L-tryptophan production [4]. We previously studied the effect of gene modification of the glutamate synthesis pathway on L-tryptophan production and selected an Escherichia coli strain with mutated gltB (encoding glutamate synthase), designated as TRTHB, which was derived from the strain TRTH in our laboratory [2]. TRTH produces high levels of L-tryptophan and can achieve a high glucose conversion rate but exhibits high acetate accumulation [5, 6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
