Phylogenetic relationships among members of the class Mollicutes deduced from rps3 gene sequences.

A gene for a ribosomal protein, rps3, was amplified by PCR and sequenced from representatives of the class Mollicutes. Alignments of the deduced amino acid sequences allowed the construction of a phylogeny that is consistent with the phylogenetic trees created from 5S and 16S rRNA comparisons, including the position of the former Acholeplasma florum on the Mycoplasma branch, rather than with the classical Acholeplasmataceae. Additional confirmation of the phylogeny comes from the deduction that the UGA triplet encodes tryptophan in the rps3 gene from Mesoplasma florum, as it does in the mycoplasmas and spiroplasmas. The sequence data from Acholeplasma axanthum 743 and Acholeplasma sp. strain J233 allow refinements to the phylogenetic tree within the Acholeplasmataceae, providing evidence that the sterol requirement of Anaeroplasma abactoclasticum (order Anaeroplasmatales) is a derived trait. It was also evident that the nonhelical plant-pathogenic members of the class Mollicutes, referred to as mycoplasma-like organisms or phytoplasmas, are more closely related to the true acholeplasmas (Acholeplasma laidlawii and strain J233) than to other members of the Mollicutes.