Study On Biochemical Identification And Fermentation Conditions Of Mutant Strains Producing L-isoleucine

Breeding of high production strain is the key to microbiologic fermentation.In the previous research we have built a mutant library with size of about 104 of the mutated RNA polymerase sigA gene of Brevibacterium flavum by global transcription machinery engineering. Nineteen mutant strains were screened from the library, which showed higher L-isoleucine yield than the original strain by flask screening. To make good use of these strains, the biochemical characteristics of these strains were analysized and the fermentation condition was studied on one of the strains. The major contents and results obtained are described as follows:1?The growth spectrum method was used to identify the biochemical characteristics of the nineteen mutant strains. Results showed that twelve among the nineteen mutants are lysine auxotrophic strains, four strains are lysine leaky mutant, one strain is methionine auxotrophic mutant, and two are not auxotrophic strains.2?The lysine auxotrophic strain 21-28, which shows good growth phenotype, was selected for further studying on fermentation conduction. Test of the genectic stablity on mutant 21-28 demonstrated that strain 21-28 keeps it genetic marker and stable L-isoleucine production during the five continuously passages. The optimum seed medium was obtained by studying the effects of different seed medium on mycelium biomass and L-isoleucine production. The single-factor experiments and the response surface experiments were adopted to optimize the medium components and fermentation parameters of mutant strain 21-28. As a result, the yield of L-isoleucine reached to 9.19 g·L-1 at the optimal conditions, which is increased by 79.49% compared to that of the original fermentation condition. These results lay a foundation for further expanding cultivation of strain 21-28.