Large Sequence Polymorphisms of the Euro-American lineage of Mycobacterium tuberculosis: a phylogenetic reconstruction and evidence for convergent evolution in the DR locus

Abstract

The Euro-American lineage of the Mycobacterium tuberculosis complex consists of 10 sublineages, each defined by a deletion of a large genomic region (RD, region of difference); by spoligotyping, that probes the polymorphism of the Direct Repeat (DR) locus, the Euro-American strains are classified into 5 lineages (T, Haarlem, LAM, S and X) and 34 sublineages, but the relationships between the RD-defined sublineages and the spoligotype groupings are largely unclear. By testing a global sample of 158 Euro-American strains, mutually exclusive deletions of RD115, RD122, RD174, RD182, RD183, RD193, RD219, RD726 or RD761 were found in 122 strains; deletion of RD724, typical of strains from Central Africa, was not found. The RD-defined sublineages, tested for katG463/gyrA95 polymorphism, belonged to Principal Genotypic Group (PGG) 2, with the exception of RD219 sublineage belonging to PGG3; the 36 strains with no deletion were of either PGG2 or 3. Based on these polymorphisms, a phylogenetic reconstruction of the Euro-American lineage, that integrates the previously reported phylogeny, is proposed. Although certain deletions were found to be associated to certain spoligotype lineages (i.e., deletion RD115 to T and LAM, RD174 to LAM, RD182 to Haarlem, RD219 to T), our analysis indicates a general lack of concordance between RD-defined sublineages and spoligotype groupings. Moreover, of the 42 spoligotypes detected among the study strains, sixteen were shared by strains belonging to different RD sublineages. IS6110-RFLP analysis of strains sharing spoligotypes confirmed a poor genetic relatedness between strains of different RD sublineages. These findings provide evidence for the occurrence of a high degree of homoplasy in the DR locus leading to convergent evolution to identical spoligotypes. The incongruence between Large Sequence Polymorphism and spoligotype polymorphism argues against the use of spoligotyping for establishing phylogenetic relationships within the Euro-American lineage.