Bäumler A J, Norris T L, Lasco T, Voight W, Reissbrodt R, Rabsch W, Heffron F
Department of Medical Microbiology and Immunology, Texas A&M University, College Station 77843-1114, USA.
J Bacteriol. 1998 Mar;180(6):1446-53. doi: 10.1128/JB.180.6.1446-1453.1998.
Speciation in enterobacteria involved horizontal gene transfer. Therefore, analysis of genes acquired by horizontal transfer that are present in one species but not its close relatives is expected to give insights into how new bacterial species were formed. In this study we characterize iroN, a gene located downstream of the iroBC operon in the iroA locus of Salmonella enterica serotype Typhi. Like iroBC, the iroN gene is present in all phylogenetic lineages of S. enterica but is absent from closely related species such as Salmonella bongori or Escherichia coli. Comparison of the deduced amino acid sequence of iroN with other proteins suggested that this gene encodes an outer membrane siderophore receptor protein. Mutational analysis in S. enterica and expression in E. coli identified a 78-kDa outer membrane protein as the iroN gene product. When introduced into an E. coli fepA cir fiu aroB mutant on a cosmid, iroN mediated utilization of structurally related catecholate siderophores, including N-(2,3-dihydroxybenzoyl)-L-serine, myxochelin A, benzaldehyde-2,3-dihydroxybenzhydrazone, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-L-lysine, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-L-lysine amide, and enterochelin. These results suggest that the iroA locus functions in iron acquisition in S. enterica.
肠杆菌中的物种形成涉及水平基因转移。因此，分析通过水平转移获得的、存在于一个物种而其近缘物种中不存在的基因，有望深入了解新细菌物种是如何形成的。在本研究中，我们对位于肠炎沙门氏菌血清型伤寒菌株iroA位点的iroBC操纵子下游的基因iroN进行了表征。与iroBC一样，iroN基因存在于肠炎沙门氏菌的所有系统发育谱系中，但在近缘物种如邦戈尔沙门氏菌或大肠杆菌中不存在。将iroN推导的氨基酸序列与其他蛋白质进行比较表明，该基因编码一种外膜铁载体受体蛋白。在肠炎沙门氏菌中的突变分析以及在大肠杆菌中的表达鉴定出一种78 kDa的外膜蛋白为iroN基因产物。当通过黏粒导入大肠杆菌fepA cir fiu aroB突变体时，iroN介导了包括N-(2,3-二羟基苯甲酰)-L-丝氨酸、黏液螯合素A、苯甲醛-2,3-二羟基苯腙、2-N,6-N-双(2,3-二羟基苯甲酰)-L-赖氨酸、2-N,6-N-双(2,3-二羟基苯甲酰)-L-赖氨酸酰胺和肠螯合素在内的结构相关儿茶酚类铁载体的利用。这些结果表明，iroA位点在肠炎沙门氏菌的铁获取中发挥作用。
