Research Article

ClpX Contributes to Innate Defense Peptide Resistance and Virulence Phenotypes of Bacillus anthracis
Shauna M. McGillivray^a, Celia M. Ebrahimi^a, Nathan Fisher^f, Mojgan Sabet^b, Dawn X. Zhang^a, Yahua Chen^g, Nina M. Haste^c, Raffi V. Aroian^d, Richard L. Gallo^b, Donald G. Guiney^b, Arthur M. Friedlander^f, Theresa M. Koehler^g, Victor Nizet^{a, c, e}

Departments of
^aPediatrics and
^bMedicine,
^cSkaggs School of Pharmacy and Pharmaceutical Sciences, and
^dDivision of Biological Sciences, University of California San Diego, La Jolla, Calif.,
^eRady Children's Hospital, San Diego, Calif.,
^fUnited States Army Medical Research Institute of Infectious Diseases, Frederick, Md., and
^gDepartment of Microbiology and Molecular Genetics, University of Texas Houston Health Science Center Medical School, Houston, Tex., USA

Address of Corresponding Author

J Innate Immun 2009;1:494-506 (DOI: 10.1159/000225955)

  Key Words

• Antimicrobial peptides
• Bacillus anthracis
• Bacterial infection
• Cathelicidins
• Hemolysis
• Innate immunity
• Protease
• Transposon mutagenesis
• Virulence factor

  Abstract

Bacillus anthracis is a National Institute of Allergy and Infectious Diseases Category A priority pathogen and the causative agent of the deadly disease anthrax. We applied a transposon mutagenesis system to screen for novel chromosomally encoded B. anthracis virulence factors. This approach identified ClpX, the regulatory ATPase subunit of the ClpXP protease, as essential for both the hemolytic and proteolytic phenotypes surrounding colonies of B. anthracis grown on blood or casein agar media, respectively. Deletion of clpX attenuated lethality of B. anthracis Sterne in murine subcutaneous and inhalation infection models, and markedly reduced in vivo survival of the fully virulent B. anthracis Ames upon intraperitoneal challenge in guinea pigs. The extracellular proteolytic activity dependent upon ClpX function was linked to degradation of cathelicidin antimicrobial peptides, a front-line effector of innate host defense. B. anthracis lacking ClpX were rapidly killed by cathelicidin and -defensin antimicrobial peptides and lysozyme in vitro. In turn, mice lacking cathelicidin proved hyper-susceptible to lethal infection with wild-type B. anthracis Sterne, confirming cathelicidin to be a critical element of innate defense against the pathogen. We conclude that ClpX is an important factor allowing B. anthracis to subvert host immune clearance mechanisms, and thus represents a novel therapeutic target for prevention or therapy of anthrax, a foremost biodefense concern.

Copyright © 2009 S. Karger AG, Basel

  Author Contacts

Dr. Victor Nizet
Department of Pediatrics and Pharmacy and Skaggs School of
Pharmacy and Pharmaceutical Sciences, University of California
9500 Gilman Drive, Mail Code 0687, La Jolla, CA 92093-0687 (USA)
Tel. +1 858 534 7408, Fax +1 858 534 5611, E-Mail vnizet@ucsd.edu

  Article Information

Received: March 3, 2009
Accepted after revision: April 7, 2009
Published online: June 18, 2009
Number of Print Pages : 13
Number of Figures : 6, Number of Tables : 0, Number of References : 40