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Infection and Immunity, November 2007, p. 5233-5239, Vol. 75, No. 11
0019-9567/07/$08.00+0     doi:10.1128/IAI.00660-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Bacillus anthracis Exosporium Protein BclA Affects Spore Germination, Interaction with Extracellular Matrix Proteins, and Hydrophobicity

Trupti N. Brahmbhatt,^1, Brian K. Janes,^2, E. Scott Stibitz,² Stephen C. Darnell,¹ Patrick Sanz,¹ Susan B. Rasmussen,¹ and Alison D. O'Brien^1*

Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, Maryland 20814,¹ Division of Bacterial, Parasitic, and Allergic Products, Centers for Biologics Evaluation and Research, 29 Lincoln Drive, Bethesda, Maryland 20892²

Received 11 May 2007/ Returned for modification 6 July 2007/ Accepted 3 August 2007

Bacillus collagen-like protein of anthracis (BclA) is the immunodominant glycoprotein on the exosporium of Bacillus anthracis spores. Here, we sought to assess the impact of BclA on spore germination in vitro and in vivo, surface charge, and interaction with host matrix proteins. For that purpose, we constructed a markerless bclA null mutant in B. anthracis Sterne strain 34F2. The growth and sporulation rates of the bclA and parent strains were nearly indistinguishable, but germination of mutant spores occurred more rapidly than that of wild-type spores in vitro and was more complete by 60 min. Additionally, the mean time to death of A/J mice inoculated subcutaneously or intranasally with mutant spores was lower than that for the wild-type spores even though the 50% lethal doses of the two strains were similar. We speculated that these in vitro and in vivo differences between mutant and wild-type spores might reflect the ease of access of germinants to their receptors in the absence of BclA. We also compared the hydrophobic and adhesive properties of bclA and wild-type spores. The bclA spores were markedly less water repellent than wild-type spores, and, probably as a consequence, the extracellular matrix proteins laminin and fibronectin bound significantly better to mutant than to wild-type spores. These studies suggest that BclA acts as a shield to not only reduce the ease with which spores germinate but also change the surface properties of the spore, which, in turn, may impede the interaction of the spore with host matrix substances.

Published ahead of print on 20 August 2007.

Editor: V. J. DiRita

Present address: Biological Defense Research Directorate, Naval Medical Research Center, Silver Spring, MD 20910.

Present address: Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109.

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