Genes of the GadX-GadW regulon in Escherichia coli.
Genes of the GadX-GadW regulon in Escherichia coli.
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大肠杆菌中 GadX-GadW 调节子的基因。
DOI：
10.1128/jb.185.10.3190-3201.2003
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发表时间：
2003
影响因子：
3.2
通讯作者：
Conway,Tyrrell
中科院分区：
文献类型：
--
作者：
Tucker,DonL;Tucker,Nancy;Ma,Zhuo;Foster,JohnW;Miranda,ReginaL;Cohen,PaulS;Conway,Tyrrell
胃酸被认为是细菌在肠道内定植的屏障。然而，大肠杆菌有三个抗酸系统，克服了这一障碍。这些系统中最有效的依赖于谷氨酸的转运和脱羧。GadX调节两个编码谷氨酸脱羧酶同型异构体的基因，这对谷氨酸脱羧酶系统至关重要，但与谷氨酸依赖的抗酸系统相关的其他基因仍有待鉴定。将gadxgene和另一个下游ac样转录因子基因gadW分别或联合突变，并将突变体的基因表达谱与野生型菌株在中性和酸化培养基中培养的基因表达谱进行比较，这些条件有利于诱导谷氨酸依赖的耐酸性。聚类分析和主成分分析鉴定出15个gadx调控的酸诱导基因。逆转录酶图谱显示这些基因由10个操纵子组成。对缺乏GadX但具有GadW的菌株的分析证实，GadX是酸性生长条件下的转录激活剂。对缺乏GadW但具有GadX的菌株的分析表明，GadW对GadX的三个靶基因具有负调控作用。缺乏GadX和GadW的菌株在大多数GadX靶基因的酸诱导上存在缺陷，但不是所有GadX靶基因都存在缺陷，这与GadW作为GadX依赖性基因激活的抑制剂和其他基因激活剂的作用一致。在某些条件下，agadx突变体的抗酸能力下降，而gadxandgadw的联合突变则更明显。然而，gadx突变体在链霉素处理小鼠模型中的定殖与野生型竞争没有缺陷，并且gadx突变体比野生型更具定殖优势。因此,E。小鼠的结肠定植似乎不需要依赖谷氨酸的耐酸性。
Acid in the stomach is thought to be a barrier to bacterial colonization of the intestine.Escherichia coli, however, has three systems for acid resistance, which overcome this barrier. The most effective of these systems is dependent on transport and decarboxylation of glutamate. GadX regulates two genes that encode isoforms of glutamate decarboxylase critical to this system, but additional genes associated with the glutamate-dependent acid resistance system remained to be identified. ThegadXgene and a second downstreamaraC-like transcription factor gene,gadW, were mutated separately and in combination, and the gene expression profiles of the mutants were compared to those of the wild-type strain grown in neutral and acidified media under conditions favoring induction of glutamate-dependent acid resistance. Cluster and principal-component analyses identified 15 GadX-regulated, acid-inducible genes. Reverse transcriptase mapping demonstrated that these genes are organized in 10 operons. Analysis of the strain lacking GadX but possessing GadW confirmed that GadX is a transcriptional activator under acidic growth conditions. Analysis of the strain lacking GadW but possessing GadX indicated that GadW exerts negative control over three GadX target genes. The strain lacking both GadX and GadW was defective in acid induction of most but not all GadX target genes, consistent with the roles of GadW as an inhibitor of GadX-dependent activation of some genes and an activator of other genes. Resistance to acid was decreased under certain conditions in agadXmutant and even more so by combined mutation ofgadXandgadW. However, there was no defect in colonization of the streptomycin-treated mouse model by thegadXmutant in competition with the wild type, and thegadX gadWmutant was a better colonizer than the wild type. Thus,E. colicolonization of the mouse does not appear to require glutamate-dependent acid resistance.