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J Bacteriol. 2011 Oct;193(19):5098-104. doi: 10.1128/JB.05658-11. Epub 2011 Aug 5.

Localization and assembly of the novel exosporium protein BetA of Bacillus anthracis.

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Department of Biochemistry, 471E Bond Life Sciences Center, 1201 E. Rollins Street, University of Missouri, Columbia, MO 65211, USA.


The exosporium of Bacillus anthracis is comprised of two distinct layers: a basal layer and a hair-like nap that covers the basal layer. The hair-like nap contains the glycoproteins BclA and, most likely, BclB. BclA and BclB are directed to assemble into the exosporium by motifs in their N-terminal domains. Here, we identify a previously uncharacterized putative gene encoding this motif, which we have named betA (Bacillus exosporium-targeted protein of B. anthracis). Like bclA, betA encodes a putative collagenlike repeat region. betA is present in several genomes of exosporium-producing Bacillus species but, so far, not in any others. Using fluorescence microscopic localization of a BetA-enhanced green fluorescent protein (eGFP) fusion protein and immunofluorescence microscopy with anti-BetA antibodies, we showed that BetA resides in the exosporium basal layer, likely underneath BclA. BetA assembles at the spore surface at around hour 5 of sporulation and under the control of BxpB, similar to the control of deposition of BclA. We suggest a model in which BclA and BetA are incorporated into the exosporium by a mechanism that depends on their similar N termini. These data suggest that BetA is a member of a growing family of exosporium proteins that assemble under the control of targeting sequences in their N termini.

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