Intragenomic heterogeneity between multiple 16S ribosomal RNA operons in sequenced bacterial genomes.

The availability of a large number of completely sequenced bacterial genomes allows the rapid and reliable determination of intragenomic sequence heterogeneity of 16S rRNA genes. In the present study we assessed the intragenomic sequence heterogeneity of 16S rRNA genes in 55 bacterial genomes, representing various phylogenetic groups. The total number of rRNA operons in genomes included ranged from 2 to 13. The maximum number of nucleotides that were different between any pair of 16S rRNA genes within a genome ranged from 0 to 19. The corresponding minimal similarity ranged from 100 to 98.74%. This indicates that the intragenomic heterogeneity between multiple 16S rRNA operons in these genomes is rather limited and is unlikely to have a profound effect on the classification of taxa. Among the multiple copies of the 16S rRNA genes present in the genomes included, 199 mutations were counted with transitions being the dominant type of mutations over the total length of the 16S rRNA gene. Most heterogeneity occurred in variable regions V1, V2, and V6.