Wyckoff Elizabeth E, Mey Alexandra R, Leimbach Andreas, Fisher Carolyn F, Payne Shelley M
University of Texas, Section of Molecular Genetics and Microbiology, 1 University Station A5000, Austin, TX 78712-0162, USA.
J Bacteriol. 2006 Sep;188(18):6515-23. doi: 10.1128/JB.00626-06.
Vibrio cholerae has multiple iron acquisition systems, including TonB-dependent transport of heme and of the catechol siderophore vibriobactin. Strains defective in both of these systems grow well in laboratory media and in the infant mouse intestine, indicating the presence of additional iron acquisition systems. Previously uncharacterized potential iron transport systems, including a homologue of the ferrous transporter Feo and a periplasmic binding protein-dependent ATP binding cassette (ABC) transport system, termed Fbp, were identified in the V. cholerae genome sequence. Clones encoding either the Feo or the Fbp system exhibited characteristics of iron transporters: both repressed the expression of lacZ cloned under the control of a Fur-regulated promoter in Escherichia coli and also conferred growth on a Shigella flexneri mutant that has a severe defect in iron transport. Two other ABC transporters were also evaluated but were negative by these assays. Transport of radioactive iron by the Feo system into the S. flexneri iron transport mutant was stimulated by the reducing agent ascorbate, consistent with Feo functioning as a ferrous transporter. Conversely, ascorbate inhibited transport by the Fbp system, suggesting that it transports ferric iron. The growth of V. cholerae strains carrying mutations in one or more of the potential iron transport genes indicated that both Feo and Fbp contribute to iron acquisition. However, a mutant defective in the vibriobactin, Fbp, and Feo systems was not attenuated in a suckling mouse model, suggesting that at least one other iron transport system can be used in vivo.
霍乱弧菌有多种铁获取系统，包括血红素和儿茶酚铁载体弧菌素的TonB依赖性转运。这两种系统有缺陷的菌株在实验室培养基和幼鼠肠道中生长良好，表明存在其他铁获取系统。在霍乱弧菌基因组序列中鉴定出了以前未表征的潜在铁转运系统，包括亚铁转运蛋白Feo的同源物和一种周质结合蛋白依赖性ATP结合盒（ABC）转运系统，称为Fbp。编码Feo或Fbp系统的克隆表现出铁转运蛋白的特征：二者都抑制了在大肠杆菌中Fur调控启动子控制下克隆的lacZ的表达，并且还使在铁转运方面有严重缺陷的福氏志贺氏菌突变体能够生长。还评估了另外两种ABC转运蛋白，但这些检测结果均为阴性。Feo系统将放射性铁转运到福氏志贺氏菌铁转运突变体中受到还原剂抗坏血酸的刺激，这与Feo作为亚铁转运蛋白的功能一致。相反，抗坏血酸抑制Fbp系统的转运，表明它转运三价铁。携带一种或多种潜在铁转运基因突变的霍乱弧菌菌株的生长表明，Feo和Fbp都有助于铁的获取。然而，在弧菌素、Fbp和Feo系统中存在缺陷的突变体在乳鼠模型中并未减毒，这表明体内至少可以使用另一种铁转运系统。
