Ecophysiology
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Cyanobacteria photosynthesize using water as the electron donor and produce oxygen as in algae,
although a small number of strains can also use hydrogen sulfide (H2S) and convert it to elemental
sulfur. In general, cyanobacteria can tolerate low oxygen conditions and concentrations of H2S that are
toxic to eukaryotic algae. This tolerance may contribute to their ability to survive in anoxic, eutrophic lake
sediments as well as in certain mat environments.