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

Abstract

To elucidate the taxonomic position of "Rhodospirillum centenum" IAM 14193^T (=ATCC 43720^T) (T=type strain), a cyst-forming anoxygenic phototrophic bacterium, the small rRNA sequences (about 1, 300 bases) were determined for the organism, two cyst-forming isolates (MT-SP-2 and MT-SP-3), Rhodopseudomonas palustris ATCC 17001^T and Erythrobacter longus JCM 6170^T by using the reverse transcription-dideoxy sequencing method. "Rhodospirillum centenum" IAM 14193^T and the two isolates had high phylogenetic affinity (98.8% homology). The sequences of the two isolates were identical. Comparative analysis of the presently determined sequences and the reference sequences (1, 107 bases) revealed that the three cyst-forming organisms belonged to the α group of the class Proteobacteria, and were distantly related to Rhodospirillum rubrum (the type species, α-1 subgroup) (89.9% homology) and the representative members of other subgroups (α-2, -3 and -4) (87.6-89.8% homology). They constituted a new phylogenetic branch in the α group. "Rhodospirillum centenum" IAM 14193^T possessed Q-9 as the major quinone but no rhodoquinones or menaquinones, that was a quinone system distinct from that of other anoxygenic phototrophs. The phylogenetic evidence and the phenotypic characteristics indicated that "Rhodospirillum centenum" IAM 14193^T did not belong to the genus Rhodospirillum. We proposed Rhodocista centenaria gen. nov., sp. nov. for the organism.