The 5S rRNA sequences of eubacteria and mycoplasmas have been analyzed and a phylogenetic tree constructed. We determined the sequences of 5S rRNA from CMstridium innocuum, Acholeplasma laidlawii, Acholeplasma modicum, Anaeroplasma bactoclasticum, Anaeroplasma abactoclasticum, Ureaplasma urealyticum, Mycoplasma mycoides mycoides, Mycoplasma pneumoniae, and Mycoplasma gallisepticum. Analysis of these and published sequences shows that mycoplasmas form a coherent phylogenetic group that, with C. innocuum, arose as a branch of the low G+C Gram-positive tree, near the lactobacilli and streptococci. The initial event in mycoplasma phylogeny was formation of the Acholeplasma branch; hence, loss of cell wall probably occurred at the time of genome reduction to lO000 MDa. A subsequent branch produced the Spiroplasma. This branch appears to have been the origin of sterol-requiring mycoplasmas. During development of the Spiroplasma branch there were several independent genome reductions, each to -500 MDa, resulting in Mycoplasma and Ureaplasma species. Mycoplasmas, particularly species with the smallest genomes, have high mutation rates, suggesting that they are in a state of rapid evolution.The wall-less prokaryotes are grouped in the class Mollicutes and are referred to as mycoplasmas (1). Mycoplasma genera (Table 1) are diverse in terms of their biochemistry, ecological niches, and genome structure. In addition, some of these organisms are significant animal, plant, and insect pathogens. Two aspects of mycoplasma biology are of particular interest. First, some mycoplasmas (i.e., Spiroplasma, Mycoplasma, Ureaplasma, and some Anaeroplasma species) are the only prokaryotes known to require cholesterol for growth; and, second, mycoplasmas have the smallest amounts of genetic information of any free-living organisms. Mycoplasma DNAs contain a low percentage of G+C.Mycoplasma genomes fall into two size classes. Acholeplasma, Spiroplasma, and Thermoplasma genomes are "1000 MDa, a size that is rare but not unknown among eubacteria (reviewed in ref.2). Mycoplasma and Ureaplasma genomes are "500 MDa, the smallest reported cellular genomes. This is only slightly larger than the theoretical minimal amount of genetic information for a cellular system (4), indicating that the complexity of mycoplasma cells must be constrained by their limited genome content.The origin and phylogenetic relationships of mycoplasmas have been of interest because these cells are the result of natural selection operating within the constraint of limited genome complexity. In the past decade, a number of studies indicated that particular biochemical properties of some Mycoplasma and Acholeplasma species are closer to those of Gram-positive than to Gram-negative eubacteria (reviewed in refs. 2 and 3). A more complete view of mycoplasma evolution came from a recent comparative analysis of 16S rRNA oligonucleotide catalogs of Acholeplasma laidlawii, Spiroplasma citri, Mycoplasma capricolum, Mycoplasma gallisepticum, and Thermoplasma acidophilum with ...

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Examination of synovial fluid in eight patients with epidemic polyarthritis following Ross River virus infection showed cell counts ranging from 1,500 to 13,800 per mm3. Stained smears were notable for a paucity of neutrophils and high proportions of monocytes and vacuolated macrophages, which were further characterised by light and electron microscopy. Ross River virus antigen was detected by specific immunofluorescence in monocytes and macrophages of four cases early in the course of the illness, but intact virus was not identified by electron microscopy or cell culture. No cell-associated C3 component of complement or immunoglobulin of IgM or IgG class was detected in any cell-type. These findings indicate that cell counts and simple smears may be useful in the early diagnosis of suspected epidemic polyarthritis, and provide further information pertinent to the pathogenesis of this disease.

Twenty-six isolates belonging to the 'Mycoplasma mycoides cluster' have been characterized by one-dimensional SDS-PAGE of their cellular proteins. A numerical classification based on the resulting patterns and using a correlation coefficient revealed four distinct phenons at a similarity (S) level of 70%, comprising: (a) bovine group 7 strains; (b) M. capricolum and F38-like strains; (c) M. mycoides subsp. capri and LC strains ('subsp. mycoides'); (d) M. mycoides subsp. mycoides (SC). At the 75% S level, they could be divided further to give eight phenons. The composition of the clusters at both levels was in good agreement with their previous classification, except for M. mycoides subsp. mycoides LC and M. mycoides subsp. capri, which were clustered in a single phenon at 70% S and could not be clearly separated at 75% S. We conclude that high-resolution SDS-PAGE, combined with computerized analysis of protein patterns, provides an extremely effective approach to the investigation of taxonomic relationships within this group of mycoplasmas.