Breeding Of Brevibacterium Flavum Strains And Optimization Of Fermentation Conditions For L-isoleucine Production

L-isoleucine which has been widely used in many fields, such as food industry, medicaldomain and photochemistry, has showed a incalculable economic value. According to thetheory of metabolic control fermentation, our work concentrate on strain improvement andoptimization of fermentation conditions with Brevibacterium flavum i10505（Met-+Ethr+α-ABr）as the initial strain. The main research contents and results are as follows:(1) We got an amino acid auxotrophic strain with resistances of α-AB and AEC whichdecreased the feedback inhibition and feedback repression of L-isoleucine during thefermentation by ultraviolet mutagenesis (UV). The final strain B.flavum KM011（Met-+LysL+Ethr+α-ABr+AECr）, under the original fermentation condition, could produce L-isoleucine by8.67g/L.(2) We optimized the culture medium by utilizing betaine, VB5, VB12as the single factorand then applied an orthogonal design. The fed-batch L-isoleucine production of strainB.flavum KM011was19.45g/L at60h, in the shake flask, under the appropriate optimalconditions.(3) Finally, under the optimal condition, we got a L-isoleucine production by B. flavumi10505and B. flavum KM011with11.85g/L and35.28g/L under fed-batch test in5Lfermenter, containing3L culture mediumwith15%(v/v) inoculum size.The innovation of our work is that we get a double mutant strain KM011with methioninedefect and lysine leakage defect. By adding betaine, VB5and VB12, fermentation period hasbeen shortern and the efficiency of L-isoleucine product has been obviously improved.