谷氨酸棒杆菌的乙醛酸循环与谷氨酸合成

Glyoxylate Cycle is Required for the Overproduction of Glutamate but is not Esse ntial for Corynebacterium glutamicum Growth on Glucose

为阐明谷氨酸棒杆菌的乙醛酸循环与菌体的生长以及谷氨酸合成之间的关系 ,以谷氨酸棒杆菌基因组测序用典型菌株CorynebacteriumglutamicumATCC 130 32为出发菌株 ,构建了乙醛酸循环途径缺失的谷氨酸棒杆菌突变株CorynebacteriumglutamicumWTΔA。该菌株没有异柠檬酸裂解酶活性 ,不能在以乙酸盐为唯一碳源的基本培养基上生长。与出发菌株ATCC130 32相比 ,WTΔA在以葡萄糖为唯一碳源的培养基上生长时不受影响 ,说明谷氨酸棒杆菌并不需要乙醛酸循环途径提供菌体生长所需的能量和生物合成反应所需的中间产物。但是 ,与出发菌株ATCC 130 32相比 ,WTΔA的谷氨酸合成能力大幅下降。

The glyoxylate cycle was hypothesed to be indispensable for glutamate overproduction in coryneform bacteria, for it was thought to fulfill anaplerotic functions and to supply energy during the growth phase. During glutamate overproduction phase, however, it has been noted that the high level of the cycle is detrimental to the glutamate production. In order to clarify the relationship between the glutamate production and the glyoxylate cycle, a chrom osomal aceA-disrupted mutant of wild-type C. glutamicum ATCC 13032 was construct ed. The isocitrate lyase (ICL) activity of the parental strain was 0\^011u/mg of protein and reached 1.980u/mg of protein after acetate induction; the mutant strain WTΔA, however, had no detectable ICL activity and was no longer able to grow on minimal medium with ac et ate as the sole carbon source. Compared with the wild-type C.glutamicum WT, the mutant strain WTΔA, exhibited the same growth rate with glucose as the sole c ar bon source, indicating glyoxylate cycle is not required for its growth on glucos e. On the contrary, the glutamate production in WTΔA was severely impaired a nd more residual glucose was found in the fermentation broth at the end of ferment ation with the mutant strain than with the wild-type strain. Further investigat ions into the relationship between the glutamate production and the glyoxylate c ycle are under the way, which may help to elucidate the mechanism of glutamate o verproduction.