Iron‐limited growth of cyanobacteria: Multiple siderophore production is a common response

During periods when levels of biologically available iron are low, cyanobacteria produce low‐molecular‐weight ferric‐specific chelators (siderophores). We investigated the frequency of siderophore production in iron‐deficient culture of freshwater and marine cyanobacteria and examined the effects of extracellular iron chelators on iron uptake in a coccoid marine species. The results confirm that iron chelate production is prevalent among freshwater and marine species and that some of these iron chelators function as siderophores. The frequent identification of catechol‐type siderophores further indicates that these iron chelators may be as important in high‐affinity iron transport as are the hydroxamic acid‐type siderophores.