中文摘要：

谷氨酸脱羧酶（GAD）能催化L-谷氨酸（Glu）脱羧生成γ-氨基丁酸（GABA）,而GAD和位于细胞膜上的Glu/GABA反向转运蛋白的协同作用则和一些细菌的耐酸机制有关。短乳杆菌GAD系统主要含有两个谷氨酸脱羧酶（Gad A和Gad B）和一个Glu/GABA反向转运蛋白（Gad C）。研究以Lactobacillus brevis CGMCC NO.1306为材料,在不同培养条件下,采用实时定量PCR的方法研究了酸胁迫对gad A、gad B和gad C表达的影响。实验结果表明,gad B和gad C组成操纵子,在菌体生长进入对数后期以后,低p H环境能极大地促进gad CB的表达,菌体的GAD活力主要由Gad B提供且在菌体生长进入稳定期时达到最大值;相对而言,gad A的表达水平几乎不受p H环境和细胞周期的影响。以上结果将为短乳杆菌GABA发酵工艺的优化和研究酸胁迫对该菌株耐酸能力的影响提供理论指导。

英文摘要：

Glutamate decarboxylase（GAD） can catalyze the decarboxylation reaction of L-glutamate（Glu） to produce γ-aminobutyric acid（GABA）. The synergetic action of GAD and membrane-located Glu/GABA antiporter is related to the acid resistance of some bacterial cells under acidic conditions. The GAD system of Lactobacillus brevis is mainly comprised of two glutamate decarboxylases（Gad A and Gad B） and a Glu/GABA antiporter（Gad C）. In this study, quantitative real-time PCR was employed to investigate the effect of acid stress on the expression of gad A, gad B and gad C in L. brevis CGMCC NO.1306 under different culture conditions. The results indicate that gad B forms an operon with gad C and the expression of gad CB is greatly upregulated in response to low ambient p H when cells enter late exponential growth phase. The GAD activity of cells is mainly from Gad B and the highest enzyme activity is observed in the stationary growth phase. In contrast, the expression of gad A is almost not affected by the ambient p H and cell cycle. These results will provide guidance for the optimization of GABA fermentation as well as the study on the ability of acid resistance of L. brevis under acid stress.