PHYLOGENETIC-RELATIONSHIPS AMONG BUDDING PURPLE BACTERIA OF THE GENUSRHODOPSEUDOMONAS

Phylogenetic relationships within a group of budding purple nonsulfur bacteria of the genus Rhodopseudomonas were studied by DNA-DNA hybridi zation. Most of the strains were new isolates from natural environment s with a wide range of physicochemical conditions. A total of 32 strai ns were analyzed, including the type strains of Rhodopseudomonas palus tris, Rps. rutila, Rps. marina, and Rps. acidophila. Nine phylogenetic ally remote clusters were revealed, showing an average DNA-DNA homolog y of 15%. One of the clusters contained the type strain of Rps. marina , isolated from marine habitats, and two new isolates from hot freshwa ter springs. These new isolates turned out to be facultative halophile s with a salinity optimum of 1-3% and were assigned to Rps. marina on the basis of their phenotypic characteristics and DNA-DNA homology of 60% with the type strain of this species. The type strain of Rps. acid ophila was not specifically related to any other strain used during th is investigation. The remaining 26 isolates and the type strains of Rp s. palustris and Rps. rutila were very similar phenotypically, but for med seven phylogenetically remote clusters including 13 genospecies; n one of the new isolates were closely related to the type strains of Rp s. palustris and Rps. rutila, which also proved to be phylogenetically distinct. Thus, the Rps. palustris-like bacteria, which are widesprea d in nature and comprise phenotypically a homogeneous group, appear to be phylogenetically diverse. The prospects for developing a classific ation system for these budding purple nonsulfur bacteria that would be in agreement with their phylogenetic relationships are discussed. Pos sible correlation between the phylogenetic relationships of these bact eria and the ecological peculiarities of their natural habitats is als o considered.