In small cell wall-lacking microorganisms, such as Mycoplasma spp, the number of ribosomal RNA operon (rrn) varies from 1-2. The goal of this study was to characterize Mycoplasma bovis intraspecies variability of the rrn loci with respect to the number of rrn, the type of Insertion like sequences (IS) and the place of their insertions within rrns. Molecular characterization of rrn loci in 70 M. bovis isolates revealed that 5 isolates contained one rrn, while 65 had two rrns. In addition, our results showed the presence of ISs, related to the ISMbov1 and ISMbov4 isomers, in 35/70 of the M. bovis isolates. The insertion of ISs was into intergenic regions (IGR) -1 or 3, comprised the putative promoter regions of rrn3 and rrn4, respectively and into IGR-5, located downstream to 23S rRNA gene (allele rrl4). Overall, relative to the IS elements, eight different configurations (A-H) of rrn loci were obtained, including those found in three annotated genomes of M. bovis. Transcriptional start site (TSS) for rrn was further examined in M. bovis strain 88127, which contains one rrn. TTS was mapped as guanine residue within the IGR-1, 60 bp upstream of the of annotated start point of the rrs gene. Our results suggest that M. bovis rrn locus serves as a hot spot for IS resulting in M. bovis intraspecies variability. The impact of the IS insertionson expression of the ribosomal genes in M. bovis isolates with different configurations of the rrn loci is currently under investigation in our laboratory.
