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Evolution towards Virulence in a Burkholderia Two-Component System.

Matthew M Schaefers1,2, Benjamin X Wang3, Nicole M Boisvert1

  • 1Division of Critical Care Medicine, Department of Anesthesiology, Critical Care and Pain Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.

Mbio
|August 10, 2021
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Mutations in the fixL gene help Burkholderia cepacia complex bacteria survive better in cystic fibrosis patients but harm their survival in soil. These fixL gene changes allow BCC to adapt to the host environment.

Keywords:
Burkholderiaevolutiontwo-component regulatory systemsvirulence regulation

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Area of Science:

  • Microbiology
  • Genetics
  • Infectious Diseases

Background:

  • The Burkholderia cepacia complex (BCC) causes serious infections in cystic fibrosis (CF) patients, often exhibiting antibiotic resistance.
  • Mutations in the fixL gene, part of the FixLJ two-component system, are frequently observed during chronic BCC infections in CF.
  • The FixLJ system regulates bacterial responses to environmental cues and is crucial for BCC virulence.

Purpose of the Study:

  • To investigate the impact of clinically observed fixL mutations on BCC fitness during host infection and in the environment.
  • To understand the molecular mechanisms by which fixL mutations affect BCC virulence and persistence.

Main Methods:

  • Comparative analysis of BCC strains with ancestral and evolved fixL sequences in macrophage survival and murine pneumonia models.
  • In vitro phosphotransfer assays to assess FixL autophosphorylation and FixJ phosphorylation.
  • LacZ reporter assays to measure fix pathway activity.
  • Soil survival assays to evaluate environmental fitness.

Main Results:

  • BCC strains with evolved fixL sequences showed increased survival in macrophages and enhanced virulence in a murine pneumonia model compared to strains with the ancestral fixL.
  • The evolved FixL protein W439S exhibited reduced autophosphorylation and FixJ phosphorylation in vitro.
  • BCC strains with evolved fixL alleles displayed reduced fix pathway activity and decreased fitness in a soil survival assay.
  • Adaptation to the host environment via fixL mutations comes at a cost to environmental fitness.

Conclusions:

  • Modulation of the FixLJ two-component system through point mutations in fixL is a key mechanism for BCC adaptation to the host environment during CF infections.
  • Evolved fixL mutations enhance BCC persistence within the host but reduce fitness in their natural soil habitat.
  • These findings highlight a trade-off between host adaptation and environmental survival for BCC pathogens.