Ghysels Bart, Ochsner Urs, Möllman Ute, Heinisch Lothar, Vasil Michael, Cornelis Pierre, Matthijs Sandra
Department of Molecular and Cellular Interactions, Laboratory of Microbial Interactions, Flanders Interuniversity Institute of Biotechnology (VIB6), Vrije Universiteit Brussel, Brussels, Belgium.
FEMS Microbiol Lett. 2005 May 15;246(2):167-74. doi: 10.1016/j.femsle.2005.04.010.
Actively secreted iron chelating agents termed siderophores play an important role in the virulence and rhizosphere competence of fluorescent pseudomonads, including Pseudomonas aeruginosa which secretes a high affinity siderophore, pyoverdine, and the low affinity siderophore, pyochelin. Uptake of the iron-siderophore complexes is an active process that requires specific outer membrane located receptors, which are dependent of the inner membrane-associated protein TonB and two other inner membrane proteins, ExbB and ExbC. P. aeruginosa is also capable of using a remarkable variety of heterologous siderophores as sources of iron, apparently by expressing their cognate receptors. Illustrative of this feature are the 32 (of which 28 putative) siderophore receptor genes observed in the P. aeruginosa PAO1 genome. However, except for a few (pyoverdine, pyochelin, enterobactin), the vast majority of P. aeruginosa siderophore receptor genes still remain to be characterized. Ten synthetic iron chelators of catecholate type stimulated growth of a pyoverdine/pyochelin deficient P. aeruginosa PAO1 mutant under condition of severe iron limitation. Null mutants of the 32 putative TonB-dependent siderophore receptor encoding genes engineered in the same genetic background were screened for obvious deficiencies in uptake of the synthetic siderophores, but none showed decreased growth stimulation in the presence of the different siderophores. However, a double knock-out mutant of ferrienterobactin receptor encoding gene pfeA (PA 2688) and pirA (PA0931) failed to be stimulated by 4 of the tested synthetic catecholate siderophores whose chemical structures resemble enterobactin. Ferric-enterobactin also failed to stimulate growth of the double pfeA-pirA mutant although, like its synthetic analogues, it stimulated growth of the corresponding single mutants. Hence, we confirmed that pirA represents a second P. aeruginosa ferric-enterobactin receptor. The example of these two enterobactin receptors probably illustrates a more general phenomenon of siderophore receptor redundancy in P. aeruginosa.
被称为铁载体的主动分泌型铁螯合剂在荧光假单胞菌的毒力和根际竞争力中发挥着重要作用，其中包括分泌高亲和力铁载体绿脓菌素和低亲和力铁载体绿脓杆菌素的铜绿假单胞菌。铁 - 铁载体复合物的摄取是一个主动过程，需要位于外膜的特定受体，这些受体依赖于内膜相关蛋白托普辛（TonB）以及另外两种内膜蛋白ExbB和ExbC。铜绿假单胞菌显然还能够通过表达其同源受体，利用多种不同的异源铁载体作为铁源。在铜绿假单胞菌PAO1基因组中观察到的32个（其中28个为推定的）铁载体受体基因就说明了这一特征。然而，除了少数几个（绿脓菌素、绿脓杆菌素、肠杆菌素）之外，绝大多数铜绿假单胞菌铁载体受体基因仍有待表征。在严重铁限制条件下，十种儿茶酚型合成铁螯合剂刺激了绿脓菌素/绿脓杆菌素缺陷型铜绿假单胞菌PAO1突变体的生长。在相同遗传背景下构建的32个推定的托普辛（TonB）依赖性铁载体受体编码基因的缺失突变体，被筛选是否在合成铁载体摄取方面存在明显缺陷，但在不同铁载体存在的情况下，没有一个显示出生长刺激减少的情况。然而，编码铁肠杆菌素受体基因pfeA（PA 2688）和pirA（PA0931）的双敲除突变体，未能被4种化学结构类似于肠杆菌素的测试合成儿茶酚铁载体刺激生长。铁 - 肠杆菌素也未能刺激双pfeA - pirA突变体的生长，尽管它与其合成类似物一样，刺激了相应单突变体的生长。因此，我们证实pirA代表铜绿假单胞菌的第二个铁肠杆菌素受体。这两种肠杆菌素受体的例子可能说明了铜绿假单胞菌中铁载体受体冗余这一更为普遍的现象。
