Unusual intragenomic and interspecific variability of Geobacillus 16S-23S rRNA internal transcribed spacers

The aim of this study was to evaluate the inter-and intraspecific as well as intragenomic variability of Geobacillus 16S-23S rRNA internal transcribed spacers without tRNA genes and to compare these sequences with sequences bearing tRNA genes. In this study the structural analysis was performed in a unique way because the length and the sequence of the structural blocks were adjusted to fit the structure of 16S-23S rRNA internal transcribed spacers of five different Geobacillus species. Our study demonstrated the mosaic-like structure of 16S-23S rRNA internal transcribed spacers in Geobacillus. Some characteristics of these spacers of geobacilli were not previously reported for other bacteria: unusually short conserved sequence in the 5' end region, some identical conserved blocks in both 5' and 3' regions of 16S-23S rRNA internal transcribed spacers, the same sequence blocks in both 16S-23S and 23S-5S rRNA intergenic spacers. Our study demonstrated quite uniform arrangement of the sequence blocks in Geobacillus thermodenitrificans. This species diverged early in the phylogenetic tree of the genus Geobacillus. For the phylogenetically recent species Geobacillus kaustophilus and Geobacillus lituanicus the low inter-and intraspecific, but high intragenomic variability, as a consequence of recent phylogenetic events, was established.