ECOLOGY OF IRON-LIMITED CYANOBACTERIA - A REVIEW OF PHYSIOLOGICAL-RESPONSES AND IMPLICATIONS FOR AQUATIC SYSTEMS

Recent studies have demonstrated that cyanobacteria are capable of res ponding to low levels of iron availability through alterations in cell ular iron requirements and by increasing their ability to scavenge iro n 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 th at these iron-chelating compounds may be important in the determinatio n of iron availability in aquatic systems. This review focuses on how cyanobacteria respond to growth-limiting levels of available iron and on how siderophores potentially alter the biological availability of i ron in the system thereby allowing the cyanobacteria to exist at low i ron availabilities. In the light of recent findings on the amount of o rganically complexed iron in aquatic systems, it is concluded that the production of siderophores by aquatic organisms may specifically dict ate the levels of biologically available iron in some aquatic systems.