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  • The EMBO Journal (2005) 24, 221 - 227
  • doi:10.1038/sj.emboj.7600495

Published online: 16 December 2004

Capsule synthesis by Bacillus anthracis is required for dissemination in murine inhalation anthrax

Melissa Drysdale1,ab, Sara Heninger2,a, Julie Hutt3, Yahua Chen1, C Rick Lyons2 and Theresa M Koehler1

  1. Department of Microbiology and Molecular Genetics, The University of Texas Houston Health Science Center, Houston, TX, USA
  2. Department of Internal Medicine, University of New Mexico Health Science Center, Albuquerque, NM, USA
  3. Lovelace Respiratory Research Institute, Albuquerque, NM, USA

Correspondence to:

Theresa M Koehler, Department of Microbiology and Molecular Genetics, University of Texas Houston Health Science Center Medical School, 6431 Fannin St, JFB 1.765, Houston, TX 77030, USA. Tel.: +1 713 500 5450; Fax: +1 713 500 5499; E-mail: Theresa.M.Koehler@uth.tmc.edu

aThese authors contributed equally to this work

bPresent address: Department of Internal Medicine, University of New Mexico Health Science Center, Albuquerque, NM 87131, USA

Received 14 June 2004; Accepted 4 November 2004

Bacillus anthracis, the agent of anthrax, produces a poly-D-glutamic acid capsule that has been implicated in virulence. Many strains missing pXO2 (96 kb), which harbors the capsule biosynthetic operon capBCAD, but carrying pXO1 (182 kb) that harbors the anthrax toxin genes, are attenuated in animal models. Also, noncapsulated strains are readily phagocytosed by macrophage cell lines, whereas capsulated strains are resistant to phagocytosis. We show that a strain carrying both virulence plasmids but deleted specifically for capBCAD is highly attenuated in a mouse model for inhalation anthrax. The parent strain and capsule mutant initiated germination in the lungs, but the capsule mutant did not disseminate to the spleen. A mutant harboring capBCAD but deleted for the cap regulators acpA and acpB was also significantly attenuated, in agreement with the capsule-negative phenotype during in vitro growth. Surprisingly, an acpB mutant, but not an acpA mutant, displayed an elevated LD50 and reduced ability to disseminate, indicating that acpA and acpB are not true functional homologs and that acpB may play a larger role in virulence than originally suspected.

  • Keywords:

    • anthracis,
    • anthrax,
    • capsule,
    • infection,
    • virulence