Gu Xinyi, Zhao Jiancun, Zhang Rongling, Yu Ruohan, Guo Tingting, Kong Jian
State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China.
College of Food Science and Engineering, Shandong Agricultural University, Tai'an, China.
Front Microbiol. 2021 Sep 10;12:691968. doi: 10.3389/fmicb.2021.691968. eCollection 2021.
() is a common bacterium inhabiting the intestines of humans and other animals. Most strains of this species can produce gamma-aminobutyric acid (GABA) the glutamate decarboxylase (GAD) system, but the presence and genetic organization of their GAD systems are poorly characterized. In this study, our bioinformatics analyses showed that the GAD system in strains was generally encoded by three genes (, , and ), together with an antiporter gene () and regulator gene (), and these genes are organized in a cluster. This finding contrasts with that for other lactic acid bacteria. SDMCC050406, a GABA producer isolated from human feces, was employed to investigate the contribution of the three genes to GABA biosynthesis. The results showed that the relative expression level of was higher than those of and in the exponential growth and stationary phases, and this was accompanied by the synchronous transcription of . After heterologous expression of the three genes in BL21 (DE3), the value of the purified GAD3 was 4.26 ± 0.48 mM, a value lower than those of the purified GAD1 and GAD2. Moreover, gene inactivation caused decreased GABA production, accompanied by a reduction in resistance to acid stress. These results indicated that plays a crucial role in GABA biosynthesis and this property endowed the strain with acid tolerance. Our findings provided insights into how strains survive the acidic environments of fermented foods and throughout transit through the stomach and gut while maintaining cell viability.
（）是一种常见的细菌，栖息于人类和其他动物的肠道中。该物种的大多数菌株可通过谷氨酸脱羧酶（GAD）系统产生γ-氨基丁酸（GABA），但其GAD系统的存在和基因组织特征尚不明确。在本研究中，我们的生物信息学分析表明，（）菌株中的GAD系统通常由三个（）基因（、和）、一个反向转运蛋白基因（）和调节基因（）编码，这些基因成簇排列。这一发现与其他乳酸菌不同。从人粪便中分离出一株GABA产生菌SDMCC050406，用于研究这三个（）基因对GABA生物合成的贡献。结果表明，在指数生长期和稳定期，的相对表达水平高于和，且这伴随着的同步转录。在（）BL21（DE）中异源表达这三个（）基因后，纯化的GAD3的（）值为4.26±0.48 mM，低于纯化的GAD1和GAD2的值。此外，基因失活导致GABA产量降低，同时对酸胁迫的抗性降低。这些结果表明，在GABA生物合成中起关键作用，这一特性赋予该菌株耐酸性。我们的研究结果为（）菌株如何在发酵食品的酸性环境中以及在整个通过胃和肠道的过程中存活并保持细胞活力提供了见解。
