Phylogenetic analysis of the mycoplasmas.

Abstract

The phylogenetic relationships between the mycoplasmas and bacteria have been established from a comparative analysis of their 16S rRNA oligonucleotide citalogs. The genera Mycoplasma, Spiroplasma, and Atholeplasma arose b degenerative evolution, as a deep branch of the subline of costridial ancestry that led to Bacillus and Lactobacillus.Thermoplasma has no specific relationship to the other mycoplasmas; it belongs with the archaebacteria.Mycoplasma is the general name for a group of prokaryotes that do not have cell walls; each cell is bounded by a single lipoprotein membrane (for reviews, see refs. 1 and 2). The various isolates have been placed in the class Mollicutes, order Mycoplasmatales and classified into the genera Mycoplasma (containing about 50 currently recognized species), Acholeplasma (6 species), Ureaplasma (1 species), and Spiroplasma (1 species). In addition, the class Mollicutes contains two genera of uncertain taxonomic position: Anaeroplasma (two species) are obligate anaerobes and Thermoplasma (one species) is an acidophilic thermophile. The taxonomy and characteristics of these genera have been reviewed recently by Tully (3). All mycoplasmas, except Acholeplasma and some Anaeroplasma isolates, require sterol for growth. The genome size of the Mycoplasma and Ureaplasma is about 0.5 X 109 daltons, that of the Acholeplasma, Spiroplasma, and Thermoplasma about 1.0 X 109 daltons. The G.C content of the cell DNA is: Mycoplasma, 23-41%; Acholeplasma, 29-35%; Ureaplasma, 28%; Spiroplasma, 26%; Anaeroplasma, 29-34%; and Thermoplasma, 46% (2).A review of the biochemical and biophysical studies of the mycoplasmas concluded that, in general, their biology is qualitatively similar to that of other prokaryotes, the only differences being quantitative ones due to the limited size of the mycoplasma cell and genome (1). In particular, mycoplasma ribosomal and transfer RNAs contain many kinds of modified bases, but in smaller amounts than reported for other prokaryotes (1, 4, 5).The origin of and relationships among mycoplasmas have been controversial for many years. Their small genome sizes and general simplicity led some workers to suggest that they might be descendants of a primitive type of organism that preceded the typical bacteria in the evolutionary progression (6). However, mycoplasmas may merely be degenerate forms. If so, there is still the question of whether mycoplasmas constitute a separate and major branch of the bacteria, as the name Mollicutes connotes, or whether they represent a diverse collection of wall-less forms derived from many different branches of bacteria.In the studies presented here, we have examined the question of mycoplasma genealogy through comparative analyses of their 16S rRNA sequences. This technique, rRNA cataloging, has been used successfully in determining the phylogenetic structure of a variety of bacterial groups (7,8). We find that the mycoplasmas are not a phylogenetically coherent group in the sense that all derive from a common ancestor, itself a mycopl...

Phylogenetic Diversity of Phytopathogenic Mycoplasmalike Organisms

“…Their genomes range in size from 680 to 1,600 kb (36). Previous analyses of 16s rRNA and 5s rRNA sequences have shown that members of the class Mollicutes are phylogenetically related to gram-positive bacteria (30,40,46,48). It has been postulated that the Mollicutes arose by degenerative evolution from clostridium-like ancestors.…”

The Subunit b of the F0F1-type ATPase of the Bacterium Mycoplasma pneumoniae Is a Lipoprotein

“…According to a widely accepted theory, these bacteria originated from Gram-positive bacteria by genome reduction (29). Since Gram-positive and all other bacteria so far analyzed do not carry the lipoprotein motif in the subunit b of the F 0 F 1 -ATPase, one can assume that mycoplasmas adopted this motif during the process of genome reduction either from another lipoprotein gene of the same cell or they received it by horizontal gene transfer.…”

‘Candidatus Phytoplasma malaysianum’, a novel taxon associated with virescence and phyllody of Madagascar periwinkle (Catharanthus roseus)

“…Phytoplasmas inhabit phloem sieve cells of infected plants and are transmitted by phloem-feeding insects, mainly leafhoppers and psyllids (Weintraub & Beanland, 2006;Hogenhout et al, 2008). Phylogenetic studies of genes encoding 16S rRNA and a large set of concatenated core housekeeping proteins have suggested that existing phytoplasmas share a common ancestor and are descended from low G+C Gram-positive bacteria in the Bacillus-Clostridium group (Woese et al, 1980;Weisburg et al, 1989;Gundersen et al, 1994;Zhao et al, 2005). Although the evolutionary events that led to the origin of the first phytoplasma remain to be unveiled, a hypothesis has been put forward (Wei et al, 2008a) based on the unique architecture discovered in phytoplasmal genomes (Jomantiene & Davis, 2006;Jomantiene et al, 2007): ancient phage predations and subsequent genetic recombination events played a formative role in triggering evolution of the phytoplasma clade.…”