Outer-membrane siderophore receptors of heterotrophic oceanic bacteria
Outer-membrane siderophore receptors of heterotrophic oceanic bacteria
复制标题
DOI：
10.4319/lo.2004.49.2.0579
复制
发表时间：
2004-03-01
影响因子：
4.5
通讯作者：
Price, NM
中科院分区：
文献类型：
--
作者：
Armstrong, E;Granger, J;Price, NM
在铁（Fe）受限的生长过程中，致病性革兰氏阴性菌利用特定受体将铁载体复合物转运穿过其外膜。此类受体在海洋异养细菌中尚未得到表征。我们使用非变性聚丙烯酰胺凝胶电泳结合试验以及用Fe - 55标记的铁载体去铁胺B（FB），对四种γ - 变形菌进行了铁 - 铁载体受体存在情况的检测。小亚基rRNA序列分析将这些细菌归为假交替单胞菌属和交替单胞菌属。两种海洋物种，即之前已表明在生长过程中能够转运和同化与FB结合的铁的盐单胞菌属的嗜盐浮游假交替单胞菌（海王星株）和交替单胞菌属的麦氏交替单胞菌（Ju188株），在铁受限条件下合成了一种外膜FB受体。当这些细菌在高铁浓度下生长时，仅检测到低浓度的受体。嗜盐浮游假交替单胞菌（海王星株）的FB受体表观分子量为79 kDa，且具有一个外向结合位点。麦氏交替单胞菌（Ju188株）的受体分子量为100 kDa。我们的方法在两种沿海物种，即红色假交替单胞菌（LMG1）和杀鱼假交替单胞菌（PWF3）中未检测到FB受体。嗜盐浮游假交替单胞菌（海王星株）和麦氏交替单胞菌（Ju188株）也能结合Fe - 55 - 高铁色素，这是一种与FB类似的三羟基肟酸铁载体。在去铁胺B浓度不断增加的情况下，用115 nmol/L的Fe - 55 - FB进行结合试验，结果显示受体蛋白结合的Fe - 55 - FB量逐渐减少，这表明受体对无铁铁载体具有强亲和力。我们的研究结果首次证明了海洋异养细菌中存在铁 - 铁载体受体。
Pathogenic gram-negative bacteria use specific receptors to transport ferric siderophore complexes across their outer membrane during iron (Fe)-limited growth. Receptors such as these have not yet been characterized in oceanic heterotrophic bacteria. We examined four species of gamma-proteobacteria for the presence of Fe-siderophore receptors with the use of a nondenaturing polyacrylamide gel electrophoresis binding assay and the siderophore ferrioxamine B (FB) labeled with Fe-55. Small-subunit rRNA sequence analysis assigned these bacteria to the genera Pseudoalteromonas and Alteromonas. Two oceanic species, Pseudoalteromonas haloplanktis (Neptune) and Alteromonas macleodii (Ju188), which were shown previously to transport and assimilate Fe bound to FB during growth, synthesized an outer-membrane FB receptor under Fe-limiting conditions. Only low concentrations of the receptors were detected in these bacteria when they were grown with high concentrations of Fe. The FB receptor of P. haloplanktis (Neptune) had an apparent molecular mass of 79 kDa and an externally oriented binding site. The molecular mass of the receptor of A. macleodii (Ju188) was 100 kDa. No FB receptors were detected by our methods in two coastal species, Pseudoalteromonas rubra (LMG1) and Pseudoalteromonas piscicida (PWF3). P. haloplanktis (Neptune) and A. macleodii (Ju188) also bound Fe-55-ferrichrome, a trihydroxamate siderophore like FB. Binding assays conducted with 115 nmol L-1 Fe-55-FB in the presence of increasing concentrations of desferrioxamine B showed a progressive decrease in the amount of Fe-55-FB bound by the receptor protein, suggesting strong affinity of the receptor for the Fe-free siderophore. Our results provide the first demonstration of Fe-siderophore receptors in oceanic heterotrophic bacteria.