Pradel E, Guiso N, Menozzi F D, Locht C
INSERM U447, Institut Pasteur de Lille, 59019 Lille Cedex, France.
Infect Immun. 2000 Apr;68(4):1919-27. doi: 10.1128/IAI.68.4.1919-1927.2000.
In gram-negative bacteria, high-affinity iron uptake requires the TonB/ExbB/ExbD envelope complex to release iron chelates from their specific outer membrane receptors into the periplasm. Based on sequence similarities, the Bordetella pertussis tonB exbB exbD locus was identified on a cloned DNA fragment. The tight organization of the three genes suggests that they are cotranscribed. A putative Fur-binding sequence located upstream from tonB was detected in a Fur titration assay, indicating that the tonB exbB exbD operon may be Fur-repressed in high-iron growth conditions. Putative structural genes of the beta-subunit of the histone-like protein HU and of a new two-component regulatory system were identified upstream from tonB and downstream from exbD, respectively. A B. pertussis DeltatonB exbB::Km(r) mutant was constructed by allelic exchange and characterized. The mutant was impaired for growth in low-iron medium in vitro and could not use ferrichrome, desferal, or hemin as iron sources. Levels of production of the major bacterial toxins and adhesins were similar in the TonB(+)/TonB(-) pair. The DeltatonB exbB mutant was still responsive to chemical modulators of virulence; thus, the BvgA/BvgS two-component system is not TonB dependent. Nevertheless, in vivo in the mouse respiratory infection model, the colonization ability of the mutant was reduced compared to the parental strain.
在革兰氏阴性菌中，高亲和力铁摄取需要TonB/ExbB/ExbD外膜复合物将铁螯合物从其特定外膜受体释放到周质中。基于序列相似性，在一个克隆的DNA片段上鉴定出了百日咳博德特氏菌的tonB、exbB、exbD基因座。这三个基因紧密排列，表明它们是共转录的。在Fur滴定试验中，在tonB上游检测到一个假定的Fur结合序列，这表明tonB exbB exbD操纵子在高铁生长条件下可能受到Fur抑制。分别在tonB上游和exbD下游鉴定出了类组蛋白HUβ亚基和一个新的双组分调节系统的假定结构基因。通过等位基因交换构建了百日咳博德特氏菌DeltatonB exbB::Km(r)突变体并对其进行了表征。该突变体在体外低铁培养基中生长受损，并且不能将高铁菌素、去铁胺或血红素用作铁源。主要细菌毒素和黏附素的产生水平在TonB(+)/TonB(-)配对中相似。DeltatonB exbB突变体仍然对毒力化学调节剂有反应；因此，BvgA/BvgS双组分系统不依赖于TonB。然而，在小鼠呼吸道感染模型的体内实验中，与亲本菌株相比，该突变体的定殖能力降低。
