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 sequenc ed from representatives of the class Mollicutes. Alignments of the ded uced amino acid sequences allowed the construction of a phylogeny that is consistent with the phylogenetic trees created from 5S and 16S rRN A comparisons, including the position of the former Acholeplasma floru m on the Mycoplasma branch, rather than with the classical Acholeplasm ataceae. Additional confirmation of the phylogeny comes from the deduc tion that the UGA triplet encodes tryptophan in the rps3 gene from Mes oplasma florum, as it does in the mycoplasmas and spiroplasmas. The se quence data from Acholeplasma axanthum 743 and Acholeplasma sp. strain J233 allow refinements to the phylogenetic tree within the Acholeplas mataceae, providing evidence that the sterol requirement of Anaeroplas ma abactoclasticum (order Anaeroplasmatales) is a derived trait. It wa s also evident that the nonhelical plant-pathogenic members of the cla ss Mollicutes, referred to as mycoplasmalike organisms or phytoplasmas , are more closely related to the true acholeplasmas (Acholeplasma lai dlawii and strain J233) than to other members of the Mollicutes.