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Exposing the third chromosome of Burkholderia cepacia complex strains as a virulence plasmid

K Agnoli1, S Schwager, S Uehlinger

  • 1Department of Microbiology, Institute of Plant Biology, University of Zürich, Zollikerstrasse 107. CH-8008 Zürich, Switzerland.

Molecular Microbiology
|December 17, 2011
PubMed

Insights

The Burkholderia cepacia complex

Area of Science:

  • Microbiology
  • Genomics
  • Pathogenesis

Background:

  • The Burkholderia cepacia complex (Bcc) comprises 17 opportunistic bacterial species.
  • Bcc bacteria pose significant threats to cystic fibrosis patients and immunocompromised individuals.
  • Bcc genomes are characterized by multiple replicons, typically three chromosomes per strain.

Purpose of the Study:

  • To investigate the role of chromosome 3 (c3) in Bcc virulence and essential functions.
  • To determine if c3 is a dispensable element or a core component of Bcc genomes.
  • To characterize the phenotypic impact of c3 loss on Bcc species.

Main Methods:

  • Transposon mutagenesis screen in a Caenorhabditis elegans infection model.
  • Construction of a c3 mini-replicon for plasmid incompatibility-based c3 curing.
  • Generation of nine c3-null strains across seven Bcc species.
  • Phenotypic characterization of c3-null mutants in various infection models and metabolic assays.

Main Results:

  • Mutants lacking c3 exhibited significantly attenuated virulence across multiple hosts (rat, zebrafish, C. elegans, G. mellonella, D. melanogaster).
  • Loss of c3 resulted in diminished antifungal activity and impaired utilization of d-xylose, fatty acids, and pyrimidines in some strains.
  • c3 was found to be essential for exopolysaccharide production and proteolytic activity in certain Bcc strains.

Conclusions:

  • Chromosome 3 (c3) is not an essential chromosomal element in the Burkholderia cepacia complex.
  • c3 functions as a large plasmid encoding crucial virulence factors, secondary metabolism, and accessory functions.
  • The dispensability of c3 offers potential avenues for novel therapeutic strategies against Bcc infections.

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