A re-evaluation of M. prototuberculosis

It has been suggested that a group of smooth tubercle bacilli, isolated from patients with tuberculosis and associated with Djibouti, East Africa, along with the seven species and subspecies that are traditional members of the Mycobacterium tuberculosis complex, should be considered a single species. This suggestion is based on the sequence similarity of the16S rRNA and segments of six housekeeping genes. The very concept of bacterial species is now subject to debate, and I follow the lead of Maynard Smith, who, in a review of the bacterial species concept, suggested that using genetic distance to define bacterial species was “arbitrary and of little merit”. If defining a species by sequence diversity alone is controversial, then it is important to carefully examine the recent claim that strains of M. tuberculosis are descendants and members of a much more ancient and large bacterial species called Mycobacterium prototuberculosis. Furthermore, given the importance of M. tuberculosis as a human pathogen and the implications for research, it is important to verify the claim that our remote hominid ancestors may have suffered from tuberculosis and that the tubercle bacilli originated in Africa.