Abstract
Two strains of gas-vacuolated heterotrophic bacteria have been isolated from freshwaters by using 0.01% peptone enrichments. Both are nonmotile, vibrioid organisms that form rings before division. In terms of these morphological traits and other characteristics, including nutritional characters and deoxyribonucleic acid base composition, these new isolates are very similar to Microcyclus aquaticus. It is proposed that they be considered strains of this species.