Analysis and application of the 16S-23S rRNA intergenic spacers in mycoplasmas

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Mycoplasmas (class Molicutes) are consisting of group of the smallest prokaryotes known that are able to grow in cell-free media, lack a cell wall, and have very small genomes with a low G+C content. Members of the genus Mycoplasma are ubiquitous in nature, and their hosts range from plants to animals. The phylogenetic analyzes of the Mycoplasma species largely depends on the 16S rRNA sequence. On the basis of the 16S rRNA sequence anlysis, the genus Mycoplasma is divided into five clsters, M.mycoides group, M.pneumoniae group, M.hyorhinis group, M.hominis group, and M.fermentans group. The genes coding for rRNA molecules of mycoplasmas are organized in operons and arranged in the order of 5'-16S-23S-5S-3', in which the individual rRNA genes are separated by internal transcribed spacer (ITS) regions. Mycoplasmas have only one or two operons for the rRNA genes. The ITS regions between the 16S and 23S rRNA genes have been shown to lack tRNA genes and to be variable in seqence and length depending on the Mycoplasma species. In this study we sequenced and analyzed the mycoplasmal ITS region between the 16S and 23S rRNA genes as an alternative to 16S rRNA,because recent studies indicate the ITS can be used as chronometers for determining the relationships of genetically closely related species, as they have higher rates of divergence than 16S rRNA genes. Our previous studies on the genus Ureaplasma indicated that the phylogenetic relationships derived from the 16S rRNA and ITS sequences are almost identical.