A smooth tubercle bacillus from Ethiopia phylogenetically close to the Mycobacterium tuberculosis complex

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• The Mycobacterium tuberculosis complex (MTBC) comprises key human and animal pathogens.
• The MTBC is hypothesized to have originated in East Africa from a Mycobacterium canettii-like ancestral pool.

Purpose of the Study:

• To investigate the evolutionary origins of the MTBC.
• To characterize a novel clinical tuberculosis strain from Ethiopia with unique phylogenetic placement.

Main Methods:

• Genomic analysis of a clinical tuberculosis isolate from Ethiopia.
• Phylogenetic analysis comparing the isolate to M. canettii and MTBC strains.
• Analysis of horizontal gene transfer traces in related strains.

Main Results:

• Discovery of a clinical tuberculosis strain in Ethiopia exhibiting M. canettii-like features but phylogenetically closer to MTBC.
• Genomic analysis revealed persistent, though reduced, horizontal gene transfer in this isolate and other M. canettii strains.
• Evidence suggests a very recent evolutionary emergence of MTBC from a free-living M. canettii-like progenitor.

Conclusions:

• The MTBC's emergence is evolutionarily recent.
• Extant derivatives of ancestral MTBC stages may exist along the Great Rift Valley.
• The study supports a continuum of evolution from M. canettii-like ancestors to the modern MTBC.