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Background  Previous studies have suggested that variations in DNA repair genes of W-Beijing strains may have led to transient mutator phenotypes which in turn may have contributed to host adaptation of this strain family. Single nucleotide polymorphism (SNP) in the DNA repair gene  mutT 1 was identified in MDR-prone strains from the Central African Republic. A  Mycobacteriumtuberculosis  H37Rv mutant inactivated in two DNA repair genes, namely  ada/alkA  and  ogt , was shown to display a hypermutator phenotype. We then looked for polymorphisms in these genes in Central African Republic strains (CAR).    Results  In this study, 55 MDR and 194 non-MDR strains were analyzed. Variations in DNA repair genes  ada/alkA  and  ogt  were identified. Among them, by comparison to  M. tuberculosis  published sequences, we found a non-sense variation in  ada/alkA  gene which was also observed in  M. bovis  AF2122 strain. SNPs that are present in the adjacent regions to the amber variation are different in  M. bovis  and in  M. tuberculosis  strain.    Conclusion  An Amber codon was found in the  ada/alkA  locus of clustered  M. tuberculosis  isolates and in  M. bovis  strain AF2122. This is likely due to convergent evolution because SNP differences between strains are incompatible with horizontal transfer of an entire gene. This suggests that such a variation may confer a selective advantage and be implicated in hypermutator phenotype expression, which in turn contributes to adaptation to environmental changes.

A non-sense mutation in the putative anti-mutator gene ada/alkA of Mycobacterium tuberculosis and M. bovis isolates suggests convergent evolution