Breeding Of L-Threonine High-yielding Strain

According to the theory of metabolic control fermentaton, the dissertation focuses on the breeding of L-Threonine high-yielding strain.L-Threonine-producing strain was isolated from soil,which was treatments by many NTG,UV and DES .Finally we obtained a high yield strain which can yield L-Threonine. The main research contents and results are as follows:(1)The method of paper chromatograghy–Rf and chromatograghy-mottle elution chromometry was defined to determine L-Threonine concentration qualitative and quantitatively in the fermentation broth.The application conditions of this method were studied.(2) According to mostly L-Threonine-production strains were bacteria in microorganisms, a bacterial selective culture medium to isolate acid-producing bacterial strains from soil samples was designed and used to isolate out 757 strains. Through the primary isolation and the compound screening,three potential strains were selected and were generally identified as to be Corynebacterium glutanicum.The best strain WS4006 could produce L-Threonine 0.18g/L, which grew well and had a short lag phase.(3) Corynebacterium glutamicum WS4006 as a starting strain was stepwise mutated with N-methyl-N'-nitro-N-nitrosoguanidine(NTG),diethyl sulfate(DES) and ultraviolet rays(UV).One L-Threonine high-producing strain NUD-12 with Met-+AHVr 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-Threonine 0.31 g/L after fermentation under the fermentation condition without being optimized.Genetic characteristics of the strain NUD-12 was very stable.