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首页> 外文期刊>Applied Microbiology >Functional γ-Aminobutyrate Shunt in Listeria monocytogenes: Role in Acid Tolerance and Succinate Biosynthesis
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Functional γ-Aminobutyrate Shunt in Listeria monocytogenes: Role in Acid Tolerance and Succinate Biosynthesis

机译：单核细胞增生李斯特菌中的功能性γ-氨基丁酸酯分流：在耐酸和琥珀酸生物合成中的作用

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Listeria monocytogenes , the causative agent of human listeriosis, is known for its ability to withstand severe environmental stresses. The glutamate decarboxylase (GAD) system is one of the principal systems utilized by the bacterium to cope with acid stress, a reaction that produces γ-aminobutyrate (GABA) from glutamate. Recently, we have shown that GABA can accumulate intracellularly under acidic conditions, even under conditions where no extracellular glutamate-GABA exchange is detectable. The GABA shunt, a pathway that metabolizes GABA to succinate, has been described for several other bacterial genera, and the present study sought to determine whether L. monocytogenes has this metabolic capacity, which, if present, could provide a possible route for succinate biosynthesis in L. monocytogenes . Using crude protein extracts from L. monocytogenes EGD-e, we show that this strain exhibits activity for the two main enzyme reactions in the GABA shunt, GABA aminotransferase (GABA-AT) and succinic semialdehyde dehydrogenase (SSDH). Two genes were identified as candidates for encoding these enzyme activities, argD (GABA-AT) and lmo0913 (SSDH). Crude protein extracts prepared from a mutant lacking a functional argD gene significantly reduced GABA-AT activity, while an lmo0913 mutant lost all detectable SSDH activity. The deletion of lmo0913 increased the acid tolerance of EGD-e and showed an increased accumulation of intracellular GABA, suggesting that this pathway plays a significant role in the survival of this pathogen under acidic conditions. This is the first report of such a pathway in the genus Listeria , which highlights an important link between metabolism and acid tolerance and also presents a possible compensatory pathway to partially overcome the incomplete tricarboxylic acid cycle of Listeria .
机译：单核细胞增生李斯特菌是人类李斯特菌病的病因，以其能够承受严重的环境压力而著称。谷氨酸脱羧酶（GAD）系统是细菌用来应对酸胁迫的主要系统之一，该反应是从谷氨酸产生γ-氨基丁酸酯（GABA）的反应。最近，我们已经表明，即使在没有可检测到细胞外谷氨酸-GABA交换的条件下，GABA也可以在酸性条件下在细胞内积累。 GABA分流是一种将GABA代谢为琥珀酸的途径，已经针对其他几个细菌属进行了描述，本研究旨在确定单核细胞增生李斯特菌是否具有这种代谢能力，如果存在，则可能为琥珀酸的生物合成提供可能的途径。在单核细胞增生李斯特菌中。使用单核细胞增生李斯特氏菌EGD-e的粗蛋白提取物，我们表明该菌株对GABA分流中的两个主要酶反应具有活性，即GABA氨基转移酶（GABA-AT）和琥珀酸半醛脱氢酶（SSDH）。确定了两个基因作为编码这些酶活性的候选基因，即argD（GABA-AT）和lmo0913（SSDH）。由缺乏功能性argD基因的突变体制备的粗蛋白提取物显着降低了GABA-AT活性，而lmo0913突变体则失去了所有可检测的SSDH活性。 lmo0913的缺失增加了EGD-e的耐酸性，并显示了细胞内GABA的积累增加，表明该途径在该病原体在酸性条件下的存活中起着重要作用。这是李斯特菌属中这种途径的第一份报告，强调了代谢与耐酸性之间的重要联系，并提出了可能的补偿途径，以部分克服李斯特菌的不完全三羧酸循环。

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