Genome-Based Taxonomic Classification of .

The bacterial phylum , characterized by a distinct gliding motility, occurs in a broad variety of ecosystems, habitats, life styles, and physiologies. Accordingly, taxonomic classification of the phylum, based on a limited number of features, proved difficult and controversial in the past, for example, when decisions were based on unresolved phylogenetic trees of the 16S rRNA gene sequence. Here we use a large collection of type-strain genomes from and closely related phyla for assessing their taxonomy based on the principles of phylogenetic classification and trees inferred from genome-scale data. No significant conflict between 16S rRNA gene and whole-genome phylogenetic analysis is found, whereas many but not all of the involved taxa are supported as monophyletic groups, particularly in the genome-scale trees. Phenotypic and phylogenomic features support the separation of as new phylum from and of as new class from . is nested within the older genus and without significant phenotypic differences; thus merging the two genera is proposed. Similarly, is proposed to be included in . is confirmed as being heterogeneous and dissected, yielding six distinct genera. is a later heterotypic synonym of . Compared to values directly calculated from genome sequences, the G+C content mentioned in many species descriptions is too imprecise; moreover, corrected G+C content values have a significantly better fit to the phylogeny. Corresponding emendations of species descriptions are provided where necessary. Whereas most observed conflict with the current classification of is already visible in 16S rRNA gene trees, as expected whole-genome phylogenies are much better resolved.