BACKGROUND : Mycobacterium tuberculosis is one of the most dangerous human pathogens, the causative agent of
tuberculosis. While this pathogen is considered as extremely clonal and resistant to horizontal gene exchange,
there are many facts supporting the hypothesis that on the early stages of evolution the development of
pathogenicity of ancestral Mtb has started with a horizontal acquisition of virulence factors. Episodes of infections
caused by non-tuberculosis Mycobacteria reported worldwide may suggest a potential for new pathogens to
appear. If so, what is the role of horizontal gene transfer in this process?
RESULTS : Availing of accessibility of complete genomes sequences of multiple pathogenic, conditionally pathogenic
and saprophytic Mycobacteria, a genome comparative study was performed to investigate the distribution of
genomic islands among bacteria and identify ontological links between these mobile elements. It was shown that
the ancient genomic islands from M. tuberculosis still may be rooted to the pool of mobile genetic vectors
distributed among Mycobacteria. A frequent exchange of genes was observed between M. marinum and several
saprophytic and conditionally pathogenic species. Among them M. avium was the most promiscuous species
acquiring genetic materials from diverse origins.
CONCLUSIONS : Recent activation of genetic vectors circulating among Mycobacteria potentially may lead to
emergence of new pathogens from environmental and conditionally pathogenic Mycobacteria. The species which
require monitoring are M. marinum and M. avium as they eagerly acquire genes from different sources and may
become donors of virulence gene cassettes to other micro-organisms.