Breeding Of L-threonine Producing Bacteria By Ntg Mutagenesis And The Determination Of Two Key Enzymes

In this paper, the breeding of L-Threonine Producing strain was studied by using the theory of metabolic control fermentaton. Besides, two key enzymes activity were determined and analysed in the whole process. The results were as follows:1. Corynebacterium glutamicum WS4006 was used to be the starting strain in the experiment. After the treatment of NTG mutagenesis and structural analogues of a-amino-β-hydroxy acid (AHV) repeatedly, an L-Threonine producing strain Y-1 (L-Met-+L-Lys-+AHVr+Ile-) was obtained. The strain could produce L-Threonine 4.14g/L after fermentation for 72 hours, which increased to 12.4 times than the strain's start production 0.31 g/L.2. Departing from the relation between the microbial metabolism and key enzyme activity, the two key enzymes's activity of several auxotroph destination strains and the relation with L-threonine production were analyzed.(1) The activity of homoserine dehydrogenase was determined by referring to the determination of dehydrogenase of sludge method. It was observed that with the strains's genetic characteristics increased,the FPase concentration of TTC increased from 0.1249 to Y-l's (L-Met-+L-Lys-+AHVr+Ile-) on WS4006 strains's, which was nearly three times greater than the starting strains's.(2) The aspartate kinase's activity of the objective was determined by taking L-aspartic acid as substrate. It turned out that after the NTG stepwise mutated and AHV resistance, Y-l's (L-Met-+L-Lys-+AHVr+Ile-) Fpase enzymic activity reached 39.1, which increased nearly two times greater than the WS4006's.