The proteomic response of a marine Vibrio to low iron and desferrioxamine siderophore bioavailability

Competition for limited iron resources is a key driver of microbial community structure in many regions of the surface ocean. The bacterial siderophores ferrioxamine and amphibactin have been identified in marine surface waters, suggesting that they may represent an important bacterial strategy for obtaining iron from a scarcely populated pool. We screened several strains of marine Vibrio for the presence of putative amphibactin biosynthesis gene homologues and amphibactin production. Whole cell proteomics, siderophore isolation, and isotopically labeled iron uptake experiments were performed. Here, we show that an amphibactin-producing marine bacterium, Vibrio cyclitrophicus str. 1F-53, harbors an independently regulated uptake pathway for ferrioxamines. Proteomic analyses identified upregulation of the amphibactin NRPS system and a putative amphibactin siderophore transporter in response to low iron concentrations. In addition, multiple other transporters were upregulated, however when desferrioxamine was present, amphibactin production decreased and the ferrioxamine receptor increased in abundance. Such cheating phenotypes, which appear widespread among marine amphibactin producers, highlight the strategies that contribute to the fitness of marine bacteria in the face of iron stress. These results demonstrate siderophore producer and cheater phenotypes and highlight the cellular restructuring which is involved due to competition for iron, that shapes the community structure of marine ecosystems.