Picocyanobacteria: the smallest cell-size cyanobacteria

Picocyanobacteria, the smallest cell-size cyanobacteria, are numerous and ubiquitous in freshwater, brackish, and marine environments. In freshwater, they are represented mainly by genera including Synechococcus, Cyanobium, and Synechocystis, and in marine waters, predominantly by Synechococcus and Prochlorococcus. Several Synechocystis and Synechococcus isolates from freshwater and brackish environments were found to produce hepatotoxins from the microcystin group. A strain of Synechococcus from the Salton Sea, capable of microcystin-LR and microcystin-YR production, was shown to be closely related to marine Synechococcus. A Synechococcus strain isolated from the Mazurian Lake BeÅ,dany was shown to have mcy genes, closely related to the Planktothrix mcy-gene cluster. Other results suggest that picocyanobacteria may be also a source of neurotoxins (neurotoxin β-N-methylamino-l-alanine), lipopolysaccharides, taste, and odour compounds as well as cytotoxic and antimicrobial compounds. These findings suggest that picocyanobacteria can be a new potential source of toxins and other bioactive compounds in freshwaters and marine environments that have, so far, been overlooked.