Deng Kaiping, Blick Robert J, Liu Wei, Hansen Eric J
Department of Microbiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9048, USA.
Infect Immun. 2006 Jul;74(7):4224-36. doi: 10.1128/IAI.01975-05.
Cells of an attenuated live vaccine strain (LVS) of F. tularensis grown under iron-restricted conditions were found to contain increased quantities of several proteins relative to cells of this same strain grown under iron-replete conditions. Mass spectrometric analysis identified two of these proteins as IglC and PdpB, both of which are encoded by genes located in a previously identified pathogenicity island in F. tularensis LVS. Regions with homology to the consensus Fur box sequence were located immediately in front of the iglC and pdpB open reading frames (ORFs), and in silico analysis of the F. tularensis Schu4 genome detected a number of predicted 5' untranslated regions that contained putative Fur boxes. The putative Fur box preceding Francisella iron-regulated gene A (figA) had the highest degree of identity with the consensus Fur box sequence. DNA microarray analysis showed that nearly 80 of the genes in the F. tularensis LVS genome were up- or down-regulated at least twofold under iron-restricted growth conditions. When tested for possible siderophore production by means of the Chrome Azurol S assay, a wild-type F. novicida strain produced a large reaction zone whereas its figA mutant produced very little reactivity in this assay. In addition, a cross-feeding experiment demonstrated that this siderophore-like activity produced by the wild-type F. novicida strain could enhance the ability of the F. novicida figA mutant to grow under iron-restricted conditions. This study provides the first identification of iron-regulated genes in F. tularensis LVS and evidence for the production of a siderophore-like molecule by F. novicida.
相对于在铁充足条件下生长的同一菌株的细胞，在铁限制条件下生长的土拉弗朗西斯菌减毒活疫苗株（LVS）的细胞被发现含有几种蛋白质的量增加。质谱分析确定其中两种蛋白质为IglC和PdpB，这两种蛋白质均由位于土拉弗朗西斯菌LVS先前鉴定的致病岛中的基因编码。与共有Fur框序列具有同源性的区域紧邻iglC和pdpB开放阅读框（ORF）之前，并且对土拉弗朗西斯菌Schu4基因组的计算机分析检测到许多包含推定Fur框的预测5'非翻译区。弗朗西斯菌铁调节基因A（figA）之前的推定Fur框与共有Fur框序列具有最高程度的同一性。DNA微阵列分析表明，土拉弗朗西斯菌LVS基因组中近80个基因在铁限制生长条件下上调或下调至少两倍。当通过铬天青S试验测试可能的铁载体产生时，野生型新凶手弗朗西斯菌菌株产生大的反应区，而其figA突变体在该试验中产生的反应性非常小。此外，交叉喂养实验表明，野生型新凶手弗朗西斯菌菌株产生的这种铁载体样活性可以增强新凶手弗朗西斯菌figA突变体在铁限制条件下生长的能力。本研究首次鉴定了土拉弗朗西斯菌LVS中的铁调节基因，并为新凶手弗朗西斯菌产生铁载体样分子提供了证据。
