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Abstract When two or more bacterial species inhabit a shared niche, often, they must compete for limited nutrients. Iron is an essential nutrient that is especially scarce in the marine environment. Bacteria can use the production, release, and re‐uptake of siderophores, small molecule iron chelators, to scavenge iron. Siderophores provide fitness advantages to species that employ them by enhancing iron acquisition, and moreover, by denying iron to competitors incapable of using the siderophore–iron complex. Here, we show that cell‐free culture fluids from the marine bacteriumVibrio fischeriES114 prevent the growth of other vibrio species. Mutagenesis reveals the aerobactin siderophore as the inhibitor. Our analysis reveals a gene, that we nameaerE, encodes the aerobactin exporter, and LuxT is a transcriptional activator of aerobactin production. In co‐culture, under iron‐limiting conditions, aerobactin production allowsV. fischeriES114 to competitively excludeVibrio harveyi, which does not possess aerobactin production and uptake genes. In contrast,V. fischeriES114 mutants incapable of aerobactin production lose in competition withV. harveyi. Introduction ofiutA,encoding the aerobactin receptor, together withfhuCDB, encoding the aerobactin importer are sufficient to convertV. harveyiinto an “aerobactin cheater.”