PHYLOGENY OF BACTEROIDES, PREVOTELLA, AND PORPHYROMONAS SPP AND RELATED BACTERIA

The phylogenetic structure of the bacteroides subgroup of the cytophaga-flavobacter-bacteroides (CFB) phylum was examined by 16S rRNA sequence comparative analysis. Approximately 95% of the 16S rRNA sequence was determined for 36 representative strains of species of Prevotella, Bacteroides, and Porphyromonas and related species by a modified Sanger sequencing method. A phylogenetic tree was constructed from a corrected distance matrix by the neighbor-joining method, and the reliability of tree branching,vas established by bootstrap analysis. The bacteroides subgroup was divided primarily into three major phylogenetic clusters which contained most of the species examined. The first cluster, termed the prevotella cluster, was composed of 16 species of Prevotella, including P. melaninogenica, P. intermedia, P. nigrescens, and the ruminal species P. ruminicola. Two oral species, P. zoogleoformans and P. heparinolytica, which had been recently placed in the genus Prevotella, did not fall within the prevotella cluster. These two species and six species of Bacteroides, including the type species B. fragilis, formed the second cluster, termed the bacteroides cluster. The third cluster, termed the porphyromonas cluster, was divided into two subclusters. The first contained Porphyromonas gingivalis, P. endodontalis, P. asaccharolytica, P. circumdentaria, P. salivosa, [Bacteroides] levii (the brackets around genus are used to indicate that the species does not belong to the genus by the sensu stricto definition), and [Bacteroides] macacae, and the second subcluster contained [Bacteroides] forsythus and [Bacteroides] distasonis. [Bacteroides] splanchnicus fell just outside the three major clusters but still belonged within the bacteroides subgroup. On the basis of bootstrap analysis, the remaining species, [Bacteroides] putredinis, Rikenella microfusus, and two misclassified, free-living species of Cytophaga, appeared to form an additional subgroup separate from the. bacteroides and other subgroups of the CFB phylum. However, on classification by single-base signatures, these species belonged within the bacteroides subgroup. Additional single-base signatures defined and differentiated clads within the bacteroides subgroup. With few exceptions, the 16S rRNA data were in overall agreement with previously proposed reclassifications of species of Bacteroides, Prevotella, and Polphyromonas. Suggestions are made to accommodate those species which do not fit previous reclassification schemes.