Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria (original) (raw)
Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe envi-ronmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cya-nobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, uni-cellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite estab-lished dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Syne-chocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influ-ence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experi-mental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Syne-chocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a signifi-cant biological component to mineral phase iron bioavailability in aquatic environments.