Breeding Of L-Tryptophan-Producing Strain And Studies On Its Fermentation Conditions

According to the theory of metabolic control fermentaton, the dissertation focuses on the breeding of L-tryptophan high-yielding strain and its fermentation conditions. The main research contents and results are as follows:1. Based on the properties of metabolic pathway of L-tryptophan in microorganisms, a bacterial selective culture medium to isolate L-tryptophan-producing bacterial strains from soil samples was designed and used to isolate out 832 strains. Through the primary isolation and the compound screening, six potential strains were selected and were generally identified as to be Corynebacterium glutanicum. The best strain JXQ3-28 could produce L-tryptophan 0.80 g/L, which grew well and had a short lag phase.2. Corynebacterium glutamicum JXQ3-28 as a starting strain was Stepwise mutated with N-methyl-N'-nitro-N-nitrosoguanidine and UV. One L-tryptophan high-producing strain SG-116 with genetic marker was screened through shake tube primary screening ,shake flask compound screening, genetic marker test, single clone isolation and continuous passage cultivation. This strain could produce L-tryptophan 7.31 g/L after fermentation under the fermentation condition without being optimized. Genetic characteristics of the strain SG-116 was very stable.3. The batch fermentation conditions of strain SG-116 in shake flask were studied in this dissertation. The proportion of seed medium and fermentation medium components were optimized by single factor,orthogonal design,uniform design experiment and DPS( Data Process System) software. The seed culture conditions and fermentation conditions were also studied. Under the optimum conditions,strain SG-116 could produce L-tryptophan 10.15g/L after incubation for 90 hours by flask-shaking batch fermentation.