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Open Access Research article

Evolution of two distinct phylogenetic lineages of the emerging human pathogen Mycobacterium ulcerans

Michael Käser1*, Simona Rondini1, Martin Naegeli1, Tim Stinear2, Francoise Portaels3, Ulrich Certa4 and Gerd Pluschke1

Author Affiliations

1 Swiss Tropical Institute, Socinstr. 57, 4002 Basel, Switzerland

2 Department of Microbiology, Monash University, Wellington Rd, Clayton 3800, Australia

3 Institute of Tropical Medicine, Antwerp 2000, Belgium

4 F. Hoffmann-La Roche Ltd., 4070 Basel, Switzerland

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BMC Evolutionary Biology 2007, 7:177  doi:10.1186/1471-2148-7-177

Published: 27 September 2007

Abstract

Background

Comparative genomics has greatly improved our understanding of the evolution of pathogenic mycobacteria such as Mycobacterium tuberculosis. Here we have used data from a genome microarray analysis to explore insertion-deletion (InDel) polymorphism among a diverse strain collection of Mycobacterium ulcerans, the causative agent of the devastating skin disease, Buruli ulcer. Detailed analysis of large sequence polymorphisms in twelve regions of difference (RDs), comprising irreversible genetic markers, enabled us to refine the phylogenetic succession within M. ulcerans, to define features of a hypothetical M. ulcerans most recent common ancestor and to confirm its origin from Mycobacterium marinum.

Results

M. ulcerans has evolved into five InDel haplotypes that separate into two distinct lineages: (i) the "classical" lineage including the most pathogenic genotypes – those that come from Africa, Australia and South East Asia; and (ii) an "ancestral" M. ulcerans lineage comprising strains from Asia (China/Japan), South America and Mexico. The ancestral lineage is genetically closer to the progenitor M. marinum in both RD composition and DNA sequence identity, whereas the classical lineage has undergone major genomic rearrangements.

Conclusion

Results of the InDel analysis are in complete accord with recent multi-locus sequence analysis and indicate that M. ulcerans has passed through at least two major evolutionary bottlenecks since divergence from M. marinum. The classical lineage shows more pronounced reductive evolution than the ancestral lineage, suggesting that there may be differences in the ecology between the two lineages. These findings improve the understanding of the adaptive evolution and virulence of M. ulcerans and pathogenic mycobacteria in general and will facilitate the development of new tools for improved diagnostics and molecular epidemiology.