Comparison of the 23S ribosomal RNA genes and the spacer region between the 16S and 23S rRNA genes of the closely related Mycobacterium avium and Mycobacterium paratuberculosis and the fast-growing Mycobacterium phlei.

The 23S rDNA sequences of Mycobacterium paratuberculosis, M. avium and M. phlei and the sequences of the spacer regions between the 16S and 23S rRNA genes were determined. The overall 23S rDNA sequence identity between M. paratuberculosis and M. avium was 99.7% (nine mismatches), showing the very close relatedness of these mycobacteria. Evolutionary distances between the five known mycobacterial 23S rRNA/rDNA sequences and those of other Gram-positive G + C-rich bacteria were determined. The 23S rDNA sequences of mycobacteria showed two inserted regions compared to the other bacteria. A mycobacterial unique region contained one mismatch between M. paratuberculosis and M. avium. An Actinomycetales-specific insertion, consisting of 111 nucleotides, was completely identical for M. paratuberculosis and M. avium. The sequence of the intergenic spacer region between 16S and 23S rDNA had a length of 278 bp for M. paratuberculosis and M. avium with only two mismatches. The spacer region of the fast-growing M. phlei was 85 bp longer. No tRNA-encoding region was found in the spacer region.