The Widespread Colonization Island of Actinobacillus actinomycetemcomitans

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Paul J Planet1, Scott C Kachlany, Daniel H Fine

  • 1Department of Microbiology, College of Physicians & Surgeons, Columbia University, 701 West 168th Street, New York, New York 10032, USA.

Nature Genetics
|April 30, 2003
PubMed

Insights

The Widespread Colonization Island, containing the tight adherence (tad) locus, is crucial for biofilm formation and surface colonization in Actinobacillus actinomycetemcomitans. Its presence across diverse species suggests horizontal gene transfer played a role in its evolution and disease association.

Area of Science:

  • Microbiology
  • Genomics
  • Evolutionary Biology

Background:

  • Genomic islands drive microbial evolution and diversification.
  • Pathogenicity islands are key examples of mobile genetic elements.
  • The tight adherence (tad) locus is involved in surface colonization and biofilm formation.

Purpose of the Study:

  • To investigate the Widespread Colonization Island and its tad locus in Actinobacillus actinomycetemcomitans.
  • To determine the role of the tad locus genes in biofilm formation and pilus assembly.
  • To explore the evolutionary history and distribution of tad-related regions in bacteria and archaea.

Main Methods:

  • Genetic analysis of tad-locus mutants in Actinobacillus actinomycetemcomitans.
  • Phylogenetic analysis comparing the tad locus to organismal phylogeny.
  • Statistical tests of congruence and tree reconciliation to assess gene transfer events.

Main Results:

  • At least 12 tad genes are essential for biofilm formation and bundled Flp pilus synthesis.
  • The tad locus appears to encode a secretion system for Flp pilus export and assembly.
  • Tad-related regions are widespread in Bacteria and Archaea, indicating horizontal gene transfer.
  • Phylogenetic analysis supports a complex evolutionary history involving recombination, horizontal transfers, duplications, and losses.

Conclusions:

  • The Widespread Colonization Island, encompassing the tad locus, is a significant factor in Actinobacillus actinomycetemcomitans colonization and pathogenesis.
  • Evidence strongly supports multiple horizontal gene transfer events shaping the evolution of the tad locus.
  • A specific horizontal transfer event likely contributed to the establishment of this region as a disease determinant.

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