Abstract
BackgroundComparative 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.ConclusionResults 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.
Highlights
Comparative genomics has greatly improved our understanding of the evolution of pathogenic mycobacteria such as Mycobacterium tuberculosis
Identification and localisation of genomic regions of difference (RDs) in M. ulcerans In a previous study we identified twelve RDs among 30 M. ulcerans strains of diverse geographic origin using a DNA microarray based on the Ghanaian reference strain Agy99 [17]
Size analysis of the deletions clustered the 30 analysed M. ulcerans strains of diverse geographic origin into five haplotypes
Summary
Comparative genomics has greatly improved our understanding of the evolution of pathogenic mycobacteria such as Mycobacterium tuberculosis. 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. M. ulcerans is the causative agent of the chronic necrotising human skin disease Buruli ulcer. Buruli ulcer is the third most common mycobacterial disease, and Western Africa is the world region most affected. The mode of transmission is thought to be from environment to human but is still very poorly understood, partly because standard molecular typing methods lack the resolution required for detailed micro-epidemiological analyses
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