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The BclB Glycoprotein of Bacillus anthracis Is Involved in Exosporium Integrity

Department of Veterinary Pathobiology and Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211,¹ Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas 66506,² Department of Pathology, Microbiology, and Immunology, University of South Carolina School of Medicine, Columbia, South Carolina 29208³

Received 15 May 2007/ Accepted 2 July 2007

Anthrax is a highly fatal disease caused by the gram-positive, endospore-forming, rod-shaped bacterium Bacillus anthracis. Spores, rather than vegetative bacterial cells, are the source of anthrax infections. Spores of B. anthracis are enclosed by a prominent loose-fitting structure called the exosporium. The exosporium is composed of a basal layer and an external hair-like nap. Filaments of the hair-like nap are made up largely of a single collagen-like glycoprotein called BclA. A second glycoprotein, BclB, has been identified in the exosporium layer. The specific location of this glycoprotein within the exosporium layer and its role in the biology of the spore are unknown. We created a mutant strain of B. anthracis Sterne that carries a deletion of the bclB gene. The mutant was found to possess structural defects in the exosporium layer of the spore (visualized by electron microscopy, immunofluorescence, and flow cytometry) resulting in an exosporium that is more fragile than that of a wild-type spore and is easily lost. Immunofluorescence studies also indicated that the mutant strain produced spores with increased levels of the BclA glycoprotein accessible to the antibodies on the surface. The resistance properties of the mutant spores were unchanged from those of the wild-type spores. A bclB mutation did not affect spore germination or kinetics of spore survival within macrophages. BclB plays a key role in the formation and maintenance of the exosporium structure in B. anthracis.

Published ahead of print on 20 July 2007.