Origin, spread and demography of the Mycobacterium tuberculosis complex

Area of Science:

• Evolutionary biology
• Microbial genetics
• Pathogen dynamics

Background:

• The evolutionary history and dissemination of the Mycobacterium tuberculosis complex (MTBC), a globally significant bacterial pathogen group, are not well understood.
• Investigating the origins and spread of MTBC is crucial for understanding host-pathogen co-evolution and disease epidemiology.

Purpose of the Study:

• To determine the evolutionary timing and geographic spread of the Mycobacterium tuberculosis complex (MTBC).
• To elucidate the host association and diversification patterns within MTBC lineages.

Main Methods:

• Utilized mycobacterial tandem repeat sequences as genetic markers for phylogenetic analysis.
• Applied Bayesian statistics and experimental data on marker variability to estimate divergence times.
• Employed coalescence analysis to infer demographic history and expansion events.

Main Results:

• Identified two distinct MTBC clades: one human-exclusive and another with mixed human and animal isolates, suggesting an original human host.
• Estimated the age of MTBC at approximately 40,000 years, aligning with early modern human migrations out of Africa.
• Observed significant recent demographic expansion in most M. tuberculosis lineages, correlating with the recent surge in human populations.

Conclusions:

• The evolutionary trajectory of MTBC is intricately linked to human population dynamics and migration patterns.
• MTBC's deep history and recent expansions highlight a dynamic co-evolutionary relationship between humans and this pathogen.
• Findings provide critical insights into the long-term association between human hosts and tuberculosis-causing bacteria.