Mey Alexandra R, Wyckoff Elizabeth E, Oglesby Amanda G, Rab Eva, Taylor Ronald K, Payne Shelley M
Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712-1095, USA.
Infect Immun. 2002 Jul;70(7):3419-26. doi: 10.1128/IAI.70.7.3419-3426.2002.
The gram-negative enteric pathogen Vibrio cholerae requires iron for growth. V. cholerae has multiple iron acquisition systems, including utilization of heme and hemoglobin, synthesis and transport of the catechol siderophore vibriobactin, and transport of several siderophores that it does not itself make. One siderophore that V. cholerae transports, but does not make, is enterobactin. Enterobactin transport requires TonB and is independent of the vibriobactin receptor ViuA. In this study, two candidate enterobactin receptor genes, irgA (VC0475) and vctA (VCA0232), were identified by analysis of the V. cholerae genomic sequence. A single mutation in either of these genes did not significantly impair enterobactin utilization, but a strain defective in both genes did not use enterobactin. When either irgA or vctA was supplied on a plasmid, the ability of the irgA vctA double mutant to use enterobactin was restored. This indicates that both VctA and IrgA transport enterobactin. We also identify the genes vctPDGC, which are linked to vctA and encode a periplasmic binding protein-dependent ABC transport system that functions in the utilization of both enterobactin and vibriobactin (VCA0227-0230). An irgA::TnphoA mutant strain, MBG40, was shown in a previous study to be highly attenuated and to have a strong colonization defect in an infant mouse model of V. cholerae infection (M. B. Goldberg, V. J. DiRita, and S. B. Calderwood, Infect. Immun. 58:55-60, 1990). In this work, a new irgA mutation was constructed, and this mutant strain was not significantly impaired in its ability to compete with the parental strain in infant mice and was not attenuated for virulence in an assay of 50% lethal dose. These data indicate that the virulence defect in MBG40 is not due to the loss of irgA function and that irgA is unlikely to be an important virulence factor.
革兰氏阴性肠道病原体霍乱弧菌生长需要铁。霍乱弧菌有多种铁获取系统，包括血红素和血红蛋白的利用、儿茶酚铁载体弧菌素的合成与运输，以及几种自身不产生的铁载体的运输。霍乱弧菌运输但不产生的一种铁载体是肠杆菌素。肠杆菌素运输需要TonB，且独立于弧菌素受体ViuA。在本研究中，通过对霍乱弧菌基因组序列的分析，鉴定出两个候选肠杆菌素受体基因，即irgA（VC0475）和vctA（VCA0232）。这两个基因中任何一个发生单突变都不会显著损害肠杆菌素的利用，但两个基因都有缺陷的菌株则不能利用肠杆菌素。当irgA或vctA通过质粒提供时，irgA vctA双突变体利用肠杆菌素的能力得以恢复。这表明VctA和IrgA都能运输肠杆菌素。我们还鉴定了vctPDGC基因，它们与vctA相连，编码一种依赖周质结合蛋白的ABC运输系统，该系统在肠杆菌素和弧菌素的利用中发挥作用（VCA0227 - 0230）。在先前的一项研究中，irgA::TnphoA突变株MBG40在霍乱弧菌感染的幼鼠模型中表现出高度减毒且具有强烈的定殖缺陷（M. B. Goldberg、V. J. DiRita和S. B. Calderwood，《感染与免疫》58:55 - 60，1990）。在这项工作中，构建了一个新的irgA突变体，该突变株在幼鼠中与亲本菌株竞争的能力没有显著受损，并且在50%致死剂量试验中其毒力也没有减弱。这些数据表明MBG40中的毒力缺陷并非由于irgA功能丧失，并且irgA不太可能是一个重要的毒力因子。
