Updated phylogenetic description of the Mycoplasma hominis cluster (Weisburg et al. 1989) based on 16S rDNA sequences

The fastidious nature of the mollicutes (mycoplasmas), their lack of a clas sic bacterial cell wall, and their very small genome, make phylogenetic pla cements of new species in this enlarging group of prokaryotes an important and valuable aid in their classification, In this report we have determined the phylogeny of the Mycoplasma hominis cluster of the hominis group. The 16S rDNA sequences from several previously described Mycoplasma species wer e determined and ten species were found to belong to the M. hominis cluster . With almost complete sequences available, the phylogenetic analysis revea led that the M, hominis cluster currently comprises 19 species, forming a d istinct clade as judged from branch lengths, bootstrap percentage values, n ucleotide signature analysis, and structural elements in the 165 rRNA molec ule. The 16S rRNA gene sequences of species in the M, hominis cluster were found to be greater than or equal to 94% similar and the range within which similarities can be used in the classification of new species is discussed . Members of the M. hominis cluster all share a major biochemical property of M, hominis, in that they hydrolyse arginine and are incapable of ferment ing glucose. This consistency in phenotypic pattern has not been found in a ny of the other phylogenetic clusters of the hominis group. Two species, th e non-cultivable agent of Grey Lung disease in rodents (tentatively named ' Candidatus Mycoplasma ravipulmonis') and the avian species Mycoplasma gypis strain B1/T1(T), were regarded as close relatives to the M. hominis cluste r, but are clearly separated from the species of this cluster. Both species formed early branches of the M, hominis cluster and should be regarded as individual lines containing one species.