High Prevalence of Diverse Insertion Sequences within the rRNA Operons of Mycoplasma bovis

Insertion sequences (ISs) are widespread in the genome ofMycoplasma bovis strain PG45, but no ISs were identified within its two tandemly positioned rRNA operons (rrn1 andrrn2 ). However, characterization of therrn locus in 70M. bovis isolates revealed the presence of ISs related to the ISMbov1 (IS30 family) and ISMbov4 (IS4 family) isomers in 35 isolates. ISs were inserted into intergenic region 1 (IGR-1) or IGR-3, which are the putative promoter regions ofrrn1 andrrn2 , respectively, and into IGR-5, located downstream of therrl2 gene. Seven different configurations (A to G) of therrn locus with respect to ISs were identified, including those in five annotated genomes. The transcriptional start site for the singlerrn operon inM. bovis strain 88127 was mapped within IGR-1, 60 bp upstream of therrs gene. Notably, only 1 nucleotide separated the direct repeat (DR) for ISMbov1 and the promoter –35 element in configuration D, while in configuration F, the −35 motif was a part of the ISMbov1 DR. Relative quantitative real-time (qRT) PCR analysis and growth rate comparisons detected a significant increase (P < 0.05) in the expression of therrs genes and in the number of viable cells during log phase growth (8, 12, and 16 h) in the strains with configuration F in comparison to strains with one or tworrn operons that did not have ISs. A high prevalence of IS elements within or close to theM. bovis rrn operon-promoter region may reflect their important role in regulation of both ribosome synthesis and function.IMPORTANCE Data presented in this study show a high prevalence of diverse ISs within theM. bovis rrn locus resulting in intraspecies variability and diversity. Such abundance of IS elements near or within therrn locus may offer a selective advantage toM. bovis . Moreover, the fact that expression of therrs genes as well as the number of viable cells increased in the group of strains with IS element insertion within a putative promoter −35 sequence (configuration F) in comparison to that in strains with one or tworrn operons that do not have ISs may serve as a basis for understanding the possible role ofM. bovis IS elements in fundamental biological processes such as regulation of ribosome synthesis and function.