Evolutionary Divergence of Aggregatibacter actinomycetemcomitans.

Area of Science:

• Microbiology
• Genomics
• Oral Health

Background:

• Aggregatibacter actinomycetemcomitans is a Gram-negative oral pathogen linked to periodontitis.
• Significant genetic diversity exists among A. actinomycetemcomitans strains.
• Understanding this heterogeneity is crucial for periodontitis research.

Purpose of the Study:

• To conduct a comprehensive genomic analysis of A. actinomycetemcomitans and the related A. aphrophilus.
• To investigate the genetic basis of heterogeneity within A. actinomycetemcomitans.
• To explore evolutionary divergence and adaptation strategies.

Main Methods:

• Whole genome sequencing of 31 A. actinomycetemcomitans and 2 A. aphrophilus strains using Illumina MiSeq.
• Sequence similarity analysis to identify core and accessory genes.
• Phylogenetic analysis using concatenated core genes and genomic island identification.

Main Results:

• Identified 3,220 unique genes (1,550 core, 1,670 accessory) across both species.
• Phylogenetic analysis delineated A. aphrophilus from A. actinomycetemcomitans, which further divided into 5 clades.
• Accessory genes, often in genomic islands acquired via horizontal gene transfer, varied significantly between clades. Clade e' strains lacked cytolethal distending toxin genes.

Conclusions:

• Genomic divergence between A. aphrophilus and A. actinomycetemcomitans occurred through gene gain/loss.
• A. actinomycetemcomitans diversified into clades with distinct gene repertoires and genomic islands.
• These genetic differences likely contribute to clade-specific adaptation and virulence in the oral environment.