Presence of GadD1 glutamate decarboxylase in selected Listeria monocytogenes strains is associated with an ability to grow at low pH
Presence of GadD1 glutamate decarboxylase in selected Listeria monocytogenes strains is associated with an ability to grow at low pH
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DOI：
10.1128/aem.71.6.2832-2839.2005
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发表时间：
2005-06-01
影响因子：
4.4
通讯作者：
Hill, C
中科院分区：
文献类型：
--
作者：
Cotter, PD;Ryan, S;Hill, C
谷氨酸脱羧酶（GAD）系统对单核细胞增生李斯特菌（Listeria monocytogenes）LO 28在低pH胁迫（<pH4.0）下的存活至关重要。GAD系统典型地涉及两种蛋白质，谷氨酸脱羧酶与谷氨酸/γ-氨基丁酸反向转运蛋白偶联，这导致每个进入系统的谷氨酸消耗细胞内质子。在原核生物中，一些菌株的L。单核细胞增多症，包括菌株LO 28，具有编码三种脱羧酶（gadD 1、gadD 2和gadD 3）和两种反向转运蛋白（gadT 1和gadT 2）的基因。它们被组织成两对（gadD 1 T1和gadD 2 T2）和一个不同的gadD 3。虽然GadD 3突变体的产生是不可能的，但对15个同基因突变体的分析证实了先前的观察结果，即GadD 2/T2主要负责在严重的酸挑战（pH 2.8）中存活。然而，我们现在已经确定GadD 1在弱酸性pH（pH 5.1）下的生长中起主要作用。当菌株变异研究表明，大量的L。当单核细胞增多性菌株（包括所有血清型4菌株）缺乏gadD 1 gadT 1对时，进行低pH生长测定。发现大多数在pH 5.1下生长不良的菌株缺乏这些基因。菌株在弱酸性条件下生长的可变能力可以解释为什么非血清型4菌株的L。单核细胞增多症在食物中占优势。
The glutamate decarboxylase (GAD) system is critical to the survival of Listeria monocytogenes LO28 at low-pH stress (< pH 4.0). The GAD system classically involves two proteins, a glutamate decarboxylase enzyme coupled to a glutamate/gamma-aminobutyrate antiporter, which results in the consumption of an intracellular proton for each glutamate entering the system. Uniquely among prokaryotes, some strains of L. monocytogenes, including strain LO28, possess genes encoding three decarboxylases (gadD1, gadD2, and gadD3) and two antiporters (gadT1 and gadT2). These are organized in two pairs (gadD1T1 and gadD2T2) and a distinct gadD3. While the creation of a gadD3 mutant has not been possible, analysis of 15 isogenic mutants has confirmed previous observations that GadD2/T2 are primarily responsible for surviving severe acid challenge (pH 2.8). However, we have now established that GadD1 plays a major role in growth at mildly acidic pHs (pH 5.1). When strain variation studies revealed that a large number of L. monocytogenes strains (including all serotype 4 strains) lack the gadD1 gadT1 pair, low-pH growth assays were carried out. It was found that the majority of strains that grew poorly at pH 5.1 lacked these genes. The strain-variable ability to grow in mildly acidic conditions may explain why non-serotype 4 strains of L. monocytogenes predominate in foods.