Scimex: The bacteria responsible for causing human tuberculosis (Mycobacterium tuberculosis) is genetically diverse and has evolved multiple lineages throughout the world. Some lineages appear to adapt to particular human populations, but of the seven human lineages, only one - lineage 4 - exists on all continents. A global genetic study published in Nature and including New Zealand data has looked at why lineage 4 was so globally successful when other lineages are so geographically restricted. The study found that lineage 4 bacteria were mainly ‘generalists’ rather than ‘specialists’, and therefore filled a larger ecological niche.
Generalist and specialist species differ in the breadth of their
ecological niches. Little is known about the niche width of obligate
human pathogens. Here we analyzed a global collection of Mycobacterium tuberculosis
lineage 4 clinical isolates, the most geographically widespread cause
of human tuberculosis. We show that lineage 4 comprises globally
distributed and geographically restricted sublineages, suggesting a
distinction between generalists and specialists. Population genomic
analyses showed that, whereas the majority of human T cell epitopes were
conserved in all sublineages, the proportion of variable epitopes was
higher in generalists. Our data further support a European origin for
the most common generalist sublineage. Hence, the global success of
lineage 4 reflects distinct strategies adopted by different sublineages
and the influence of human migration.