Ecology of iron-limited cyanobacteria: a review of physiological responses and implications for aquatic systems

Recent studies have demonstrated that cyanobacteria are capable of responding to low levels of iron availability through alterations in cellular iron requirements and by increasing their ability to scavenge iron from the environment through the activation of siderophore-mediated high-affinity transport systems. The significant amount of evidence In the literature on siderophore production by cyanobacteria suggests that these iron-chelating compounds may b e important in the determination of iron availability in aquatic systems. This review focuses on how cyanobacteria respond to growthlimiting levels of available iron and on how siderophores potentially alter the biological availability of iron in the system thereby allowing the cyanobacteria to e x ~s t at low iron availabilities. In the light of recent findings on the amount of organically complexed iron in aquatic systems, it is concluded that the production of siderophores by aquatic organisms may specifically dictate the levels of biologically available iron in some aquatic systems.