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Novel large-scale chromosomal transfer in Bacteroides fragilis contributes to its pan-genome and rapid environmental

Fasahath Husain1, Kevin Tang2, Yaligara Veeranagouda3

  • 11​Brentwood Biomedical Research Institute, Los Angeles, CA, USA.

Microbial Genomics
|December 7, 2017
PubMed

Insights

Large chromosomal segments transferred between Bacteroides fragilis strains, driving antigenic diversity and adaptation. This process disseminates the B. fragilis pan-genome and can confer pathogenic traits.

Area of Science:

  • Microbiology
  • Genetics
  • Bacterial Pathogenesis

Background:

  • Bacteroides fragilis is a key human gut microbe.
  • This bacterium can cause severe infections outside the gastrointestinal tract.
  • Understanding its genetic adaptability is crucial for public health.

Purpose of the Study:

  • To investigate the mechanisms and consequences of large chromosomal segment transfer in Bacteroides fragilis.
  • To determine how such transfers impact bacterial adaptation, diversity, and pathogenicity.

Main Methods:

  • Conjugation experiments were performed between multidrug-resistant B. fragilis HMW615 and B. fragilis 638R.
  • Whole-genome sequencing and comparative genomic analysis were used to identify transferred segments.
  • Bioinformatic tools were employed to analyze gene content, including polysaccharide biosynthesis loci, shufflons, and restriction/modification systems.

Main Results:

  • Demonstrated transfer and recombination of large chromosomal segments (~435 Kb) between B. fragilis strains.
  • Transferred segments replaced existing loci, including polysaccharide biosynthesis genes and DNA inversion-controlled shufflons.
  • Introduced new shufflons encoding restriction/modification systems and antibiotic resistance genes.
  • Identified potential roles for conjugative transposon-like genes and an integrative conjugative element (ICE5) in mediating transfer.

Conclusions:

  • Chromosomal transfer significantly drives antigenic diversity and nutrient adaptation in Bacteroides.
  • This process facilitates the spread of the extensive B. fragilis pan-genome.
  • Rapid adaptation to environmental changes and acquisition of pathogenic characteristics are key outcomes.
Keywords:
Bacteroides fragilishorizontal transmissionpolysaccharide capsulesrestriction modification system

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