Comparative evaluation of sequence analysis of 16S rRNA and rpoB genes for identification of aquatic mycobacteria

The nucleotide sequences of partial 16S rRNA and bacterial RNA polymerase beta-subunit (rpoB) genes for 57 mycobacterial strains were determined. Compared to the 16S rRNA gene sequences, variable regions were scattered along the whole fragment sequence, indicating that the rpoB gene is more polymorphic. Unlike 16S rRNA sequences, species variation was observed within M. fortuitum strains. The topology of the rpoB-based phylogenetic tree was almost the same as that of the 16S rRNA sequence analysis. These results suggest that the rpoB gene is a highly conserved gene, and taxonomical studies based on this gene may be comparable with similar studies based on the 16S rRNA gene. The overall mean distance for rpoB-gene-based sequences was 2.5 times greater than that of the 16S rRNA gene for all 57 mycobacterial strains examined. However, some slowly growing mycobacteria could not be differentiated based on rpoB gene sequences. Moreover, a bootstrap value above 70% was observed for 13 nodes, while this value was 14 nodes in the case of 16S rRNA sequences. To the best of our knowledge, this is the first investigation evaluating the use of 16S rRNA and rpoB sequence analyses for identification of aquatic mycobacteria obtained from diverse geographical locations.