Abstract
DNA base composition and DNA--DNA hybridization among the cyanobacterial genus Microcystis were determined using nine axenic Microcystis strains, including the three 'morphological' species of Microcystis aeruginosa, Microcystis viridis and Microcystis wesenbergii. These Microcystis species showed a similar DNA base composition (42.1--42.8 mol% G+C) and demonstrated more than 70% DNA relatedness, confirming their synonymy based on bacterial criteria.