The evolution of mycobacterial pathogenicity: clues from comparative genomics

Area of Science:

• Genomics
• Microbiology
• Evolutionary Biology

Background:

• Slow-growing mycobacteria present complex challenges in understanding pathogenesis and evolution.
• The Mycobacterium tuberculosis complex is highly conserved, with limited single-nucleotide polymorphisms.
• Genome plasticity is crucial for adaptation and evolution in bacterial pathogens.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the evolution and phenotypic diversity of slow-growing mycobacteria.
• To identify the primary drivers of genome plasticity within the Mycobacterium tuberculosis complex.
• To explore the role of genomic changes in pathogen attenuation, exemplified by the BCG vaccine strain.

Main Methods:

• Comparative genomics analyses.
• Investigation of insertion and deletion events (InDels).
• Examination of recombinational events, insertion sequence (IS)-mediated events, and DNA sequence expansions/contractions.

Main Results:

• Insertion and deletion events (InDels) are identified as the principal source of genome plasticity in the Mycobacterium tuberculosis complex.
• InDels arise from various mechanisms including recombination, IS activity, repetitive DNA expansion, and replication errors.
• Comparative genomic data suggest gene loss is a significant factor in the evolution of slow-growing mycobacterial pathogens.

Conclusions:

• InDels are key drivers of genomic variation and adaptation in slow-growing mycobacteria.
• Gene loss plays a role in the evolutionary trajectory of these pathogens.
• Genomic alterations, including gene loss, may explain the attenuation of the Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine strain.