DNA-DNA and rRNA-DNA hybridization studies in the genus Ectothiorhodospira and other purple sulfur bacteria

DNA-DNA hybridization reveals low DNA homologies (about 14%) between the species of Ectothiorhodospira genus and indicate clearly that the degree of divergence within this genus exceeds the interspecific level. The degree of genome similarities of E. mobilis and E. vacuolata (more than 80% homology) is high and characteristic for the strains of one and the same species.The results of rRNA-DNA and secondary DNA-DNA hybridization indicate the following: Ectothiorhodospira and Thiocapsa are far less related than the genera of one and the same family; the genus Ectothiorhodospira is equidistant from both families of purple sulfur and nonsulfur bacteria. Thus Ectothiorhodospira is a taxon of a higher rank than a genus; we agree with Imhoff's proposal of a new family Ectothiorhodospiraceae.