The role of siderophores for bacterial community building.

Iron is an essential trace element for most organisms on earth including bacteria. However, iron in the environment generally occurs in its ferric (Fe3+) form and is therefore not bioavailable. To capture ferric iron, many bacteria produce siderophores - a class of secreted secondary metabolites that scavenge iron from natural sources and allow iron uptake via specific transporters. As secreted molecules, siderophores inevitably affect other community members, and recent evidence suggests that siderophores play important roles in shaping interaction networks between strains and species in complex communities. In this review, we first explain how siderophores induce ecological interactions among bacteria ranging from mutualism to exploitation to competition. Subsequently, we elaborate on how physicochemical properties of siderophores, like production rates, diffusibility, stability, iron affinity, and chemical specificity, influence the type and strength of siderophore-mediated interactions. Finally, we introduce various scenarios to illustrate how siderophore interaction networks and community building can arise. We conclude our review by highlighting that our knowledge of siderophore interaction networks is restricted to a few taxa that were studied in detail, and that future work should break this limitation by studying the role of siderophore-mediated interactions at the microbiome scale.