A glutamate decarboxylase system protects Listeria monocytogenes in gastric fluid
A glutamate decarboxylase system protects Listeria monocytogenes in gastric fluid
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DOI：
10.1046/j.1365-2958.2001.02398.x
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发表时间：
2001-04-01
影响因子：
3.6
通讯作者：
Hill, C
中科院分区：
文献类型：
--
作者：
Cotter, PD;Gahan, CGM;Hill, C
我们观察到谷氨酸极大地增强了胃液中单核细胞增生李斯特菌的存活，这一现象与谷氨酸脱羧酶活性（GAD）直接相关。谷氨酸介导的酸耐受性在其他肠属中与GAD系统相关，其中谷氨酸被内化并转化为γ-氨基丁酸（消耗细胞内质子），其随后通过膜定位的反向转运蛋白交换为另一种细胞外谷氨酸。L.单核细胞增多症LO 28揭示了两种谷氨酸脱羧酶同源物的存在，命名为gadA和gadB，其差异表达。gadB基因与上游基因gadC串联共转录，gadC编码潜在的谷氨酸/γ-氨基丁酸反向转运蛋白。该转录本的表达在轻度酸胁迫（pH 5.5）下上调。相比之下，单顺反子gadA信息的表达较弱，并且不被弱酸处理诱导。非极性缺失突变导致GAD活性水平急剧下降，并且对于静止期和对数期培养物，以LO 28> Delta gadA > Delta gadB = Delta gadC > Delta gadAB的顺序伴随着耐酸性下降。Delta gadAB突变体对离体猪和合成人胃液的灵敏度证明了GAD系统在促进摄取后生物体在胃中和其他低pH环境中的存活方面的明确作用。此外，不同菌株间GAD活性水平的差异。单核细胞增多症与对胃液的耐受水平显著相关。敏感菌株，包括测序的L。单核细胞增多症EGD表现出GAD活性水平降低。本研究表明，L.单核细胞增生菌株是在胃环境中生存的绝对要求。
We observed that glutamate greatly enhances the survival of Listeria monocytogenes in gastric fluid, a phenomenon that is directly linked to glutamate decarboxylase activity (GAD). Glutamate-mediated acid tolerance has been associated in other intestinal genera with the GAD system, in which glutamate is internalized and converted to gamma -aminobutyrate (consuming an intracellular proton) that is subsequently exchanged for another extracellular glutamate via a membrane-located antiporter. Molecular analysis of L. monocytogenes LO28 revealed the presence of two glutamate decarboxylase homologues, designated gadA and gadB, that are differentially expressed. The gadB gene is co-transcribed in tandem with an upstream gene, gadC, which encodes a potential glutamate/gamma -aminobutyrate antiporter. Expression of this transcript is upregulated in response to mild acid stress (pH 5.5). In contrast, expression of the monocistronic gadA message was weaker and was not induced by mild acid treatment. Non-polar deletion mutations resulted in a dramatic decrease in the level of GAD activity and a concomitant decrease in acid resistance in the order LO28 > Delta gadA > Delta gadB = Delta gadC > Delta gadAB for both stationary and logarithmic phase cultures. The exquisite sensitivity of the Delta gadAB mutant to ex vivo porcine and synthetic human gastric fluid demonstrates a clear role for the GAD system in facilitating survival of the organism in the stomach after ingestion and in other low-pH environments. Furthermore, variations in levels of GAD activity between different strains of L. monocytogenes correlate significantly with levels of tolerance to gastric fluid. Sensitive strains, which include the sequenced L. monocytogenes EGD, exhibit reduced levels of GAD activity. It is clear from this study that expression of GAD by L. monocytogenes strains is an absolute requirement for survival in the stomach environment.