Cyanobacteria are globally important primary producers and nitrogen fixers with high iron demands. Low ambient dissolved iron concentrations in many aquatic environments mean that these organisms must maintain sufficient and selective transport of iron into the cell. However, the nature of iron transport pathways through the cyanobacterial outer membrane remains obscure. Here we present multiple lines of experimental evidence that collectively support the existence of a novel class of substrate‐selective iron porin, Slr1908, in the outer membrane of the cyanobacterium Synechocystis sp. PCC 6803. Elemental composition analysis and short‐term iron uptake assays with mutants in Slr1908 reveal that this protein is primarily involved in inorganic iron uptake and contributes less to the accumulation of other metals. Homologues of Slr1908 are widely distributed in both freshwater and marine cyanobacteria, most notably in unicellular marine diazotrophs. Complementary experiments with a homologue of Slr1908 in Synechococcus sp. PCC 7002 restored the phenotype of Synechocystis knockdown mutants, showing that this siderophore producing species also possesses a porin with a similar function in Fe transport. The involvement of a substrate‐selective porins in iron uptake may allow cyanobacteria to tightly control iron flux into the cell, particularly in environments where iron concentrations fluctuate.

中文翻译：

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独特的孔蛋白可通过蓝细菌外膜思考铁的选择性转运

蓝细菌是全球重要的初级生产者和固氮需求较高的固氮剂。在许多水生环境中，环境中溶解的铁浓度较低，这意味着这些生物必须保持铁向细胞中的选择性迁移。然而，通过蓝细菌外膜的铁运输途径的性质仍然不清楚。在这里，我们提供多行实验证据，共同支持在蓝藻集胞藻的外膜中存在一类新型的底物选择性铁孔蛋白Srr1908。sp。PCC 6803. Slr1908中的突变体的元素组成分析和短期铁吸收测定表明，该蛋白主要参与无机铁的吸收，对其他金属的积累贡献较小。Slr1908的同系物广泛分布在淡水和海洋蓝细菌中，最主要的是在单细胞海洋重氮细菌中。互补实验与Syr1908在Synechococcus sp。的同系物。PCC 7002恢复了集胞藻的表型敲低突变体，表明该产生铁载体的物种还具有在铁转运中具有相似功能的孔蛋白。底物选择性孔蛋白参与铁的吸收，可能会使蓝细菌严格控制铁向细胞的通量，特别是在铁浓度波动的环境中。