过表达hom基因对谷氨酸棒杆菌发酵L-异亮氨酸的影响

谷氨酸棒杆菌（Corynebacterium glutamicum）中hom基因编码的高丝氨酸脱水酶为L-异亮氨酸合成过程的关键酶，本研究通过在L-异亮氨酸生产菌cglutamicum YILW中过表达高丝氨酸脱水酶，考察过表达高丝氨酸脱水酶对发酵卜异亮氨酸产量的影响．以L-异亮氨酸生产菌cglutamicum YILW基因组为模板克隆horn基因，将horn基因与表达载体pXMJ19连接构建出重组质粒pXMJ19-hom，再转入Cglutamicum YILW构建C．glutamicum YILW（pXMJ19．hom）．通过5L罐发酵研究重组质粒对工程菌的生长、耗糖、L-异亮氨酸产量及副产物积累等方面的影响．结果显示，重组酶的表达使菌株对卜苏氨酸的抗反馈抑制作用得到加强．最终L-异亮氨酸和L-蛋氨酸积累量分别为36．5g／L和2．8g／L，分别较出发菌株提高7％和33％，同时L-赖氨酸合成量仅为2．1g／L，较出发菌株降低了63．8％．

Effects of Overexpression of Homoserine Dehydratase on L-Isoleucine Production in Corynebacterium glutamicum

Homoserine dehydratase, a key enzyme of L-isoleucine synthesis process, is encoded by the horn gene in Cory- nebacterium glutamicum. The effect of overexpressed homoserine dehydratase in C. glutamicum YILW on the production of L-isoleucine was studied. The horn gene was PCR amplified using C. glutamicum YILW genomic DNA as template and then inserted into a multicopy plasmid pXMJ19 to construct a recombined expression plasmid pXMJ19-hom. The recombined plasmid was then transformed into C. glutamicum YILW to construct recombined C. glutamicum YILW （pXMJ 19-horn）. The effects of pXMJ19-hom on cell growth, glucose consumption rate, yield of L-isoleucine and accumulation of byproducts were investigated by using 5 L batch fermentation. Enzyme studies showed that the recombined homoserine dehydratase expressed in C. glutamicum YILW （pXMJ 19-horn） strain was much less sensitive to threonine inhibition. Compared with the original strain, the yields of L-isoleucine and L-methionine by using C. glutamicum YILW （pXMJ 19-hom）were 36.5 g/L and 2.8 g/L, which indicated on increase of 7% and 33% respectively, but the yield of L-lysine was only 2.1 g/L, decreased by 63.8%.