RHODOCISTA-CENTENARIA GEN-NOV, SP-NOV, A CYST-FORMING ANOXYGENIC PHOTOSYNTHETIC BACTERIUM AND ITS PHYLOGENETIC POSITION IN THE PROTEOBACTERIA ALPHA-GROUP

To elucidate the taxonomic position of ''Rhodospirillum centenum'' IAM 14193T (= ATCC 43720T) (T = type strain), a cyst-forming anoxygenic p hototrophic bacterium, the small rRNA sequences (about 1,300 bases) we re determined for the organism, two cyst-forming isolates (MT-SP-2 and MT-SP-3), Rhodopseudomonas palustris ATCC 17001T and Erythrobacter lo ngus JCM 6170T by using the reverse transcription-dideoxy sequencing m ethod. ''Rhodospirillum centenum'' IAM 14193T and the two isolates had high phylogenetic affinity (98.8% homology). The sequences of the two isolates were identical. Comparative analysis of the presently determ ined sequences and the reference sequences (1,107 bases) revealed that the three cyst-forming organisms belonged to the alpha group of the c lass Proteobacteria, and were distantly related to Rhodospirillum rubr um (the type species, alpha-1 subgroup) (89.9% homology) and the repre sentative members of other subgroups (alpha-2, -3 and -4) (87.6-89.8% homology). They constituted a new phylogenetic branch in the alpha gro up. ''Rhodospirillum centenum'' IAM 14193T possessed Q-9 as the major quinone but no rhodoquinones or menaquinones, that was a quinone syste m distinct from that of other anoxygenic phototrophs. The phylogenetic evidence and the phenotypic characteristics indicated that ''Rhodospi rillum centenum'' IAM 14193T did not belong to the genus Rhodospirillu m. We proposed Rhodocista centenaria gen. nov., sp. nov. for the organ ism.