Genomic Comparisons Reveal Microevolutionary Differences in Mycobacterium abscessus Subspecies

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• Mycobacterium abscessus complex comprises three subspecies (M. abscessus, M. massiliense, M. bolletii) known for opportunistic infections.
• Distinct clinical and biological characteristics among subspecies suggest underlying evolutionary divergence.
• The evolutionary forces shaping these differences remain largely unknown.

Purpose of the Study:

• To investigate the roles of homologous recombination and positive selection in the diversification of the Mycobacterium abscessus complex.
• To identify specific genes and evolutionary processes contributing to subspecies-specific traits.

Main Methods:

• Comparative genomics analysis of 243 Mycobacterium abscessus strains from the NCBI Refseq database.
• Phylogenetic analysis using Minimum Spanning Tree and MUMi-based genomic distances.
• Identification of positively selected genes using Maximum Likelihood analysis (dN/dS ratios).
• Genome-wide alignment of concatenated locally-collinear blocks to assess recombination patterns.

Main Results:

• Phylogenetic analyses clearly separated the three subspecies.
• Homologous recombination was identified as a more significant driver of diversification than mutation and positive selection.
• M. massiliense exhibited higher recombination frequencies compared to the other subspecies.
• Recombined segments originated from diverse intra-species and inter-species sources.

Conclusions:

• Recombination plays a crucial role in the independent evolution and diversification of Mycobacterium abscessus subspecies.
• Specific gene sets potentially responsible for subspecies-specific features were identified.
• Understanding these evolutionary dynamics is key to addressing the clinical variations observed within the M. abscessus complex.