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Expression and contribution to virulence of each polysaccharide capsule of Bacillus cereus strain G9241

Jennifer M Scarff1, Yuliya I Seldina1, James M Vergis1

  • 1Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD, United States of America.

Plos One
|August 23, 2018
PubMed

Insights

Bacillus cereus G9241 produces two capsules, hyaluronic acid (HA) and tetrasaccharide (TS), encoded on virulence plasmids. Loss of the HA capsule significantly reduced bacterial virulence more than the TS capsule in mouse models.

Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Molecular Biology

Background:

  • Bacillus cereus strain G9241 exhibits anthrax-like illness symptoms.
  • Virulence in G9241 is plasmid-dependent, involving pBCXO1 and pBC210.
  • Both plasmids harbor multi-gene capsule loci, producing hyaluronic acid (HA) and tetrasaccharide (TS) capsules.

Purpose of the Study:

  • To characterize the tetrasaccharide (TS) capsule locus on the pBC210 plasmid.
  • To investigate the transcriptional organization of the TS capsule locus.
  • To determine the contribution of HA and TS capsules to Bacillus cereus G9241 virulence.

Main Methods:

  • Identification of promoter regions for the TS capsule operons.
  • Construction of isogenic mutants deficient in HA or TS capsule production.
  • Determination of Lethal Dose 50% (LD50) in mouse models via subcutaneous and intranasal routes.

Main Results:

  • The pBC210 capsule locus is transcribed as two operons.
  • Deletion of the hyaluronic acid (HA) capsule gene resulted in greater attenuation of virulence compared to the tetrasaccharide (TS) capsule deletion.
  • Both HA and TS capsules contribute to G9241 virulence, but to different extents.

Conclusions:

  • The study elucidates the transcriptional regulation of the unique TS capsule.
  • Hyaluronic acid capsule plays a more critical role in Bacillus cereus G9241 virulence than the TS capsule.
  • These findings highlight the differential impact of plasmid-encoded capsules on bacterial pathogenesis.

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