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Non‐uniform assembly of the Bacillus anthracis exosporium and a bottle cap model for spore germination and outgrowth
Author(s) -
Steichen Christopher T.,
Kearney John F.,
Turnbough Charles L.
Publication year - 2007
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2007.05658.x
Subject(s) - biology , bacillus anthracis , spore , mutant , glycoprotein , cell wall , monoclonal antibody , spore germination , microbiology and biotechnology , biochemistry , genetics , antibody , bacteria , gene
Summary Spores of Bacillus anthracis are enclosed by an exosporium composed of a basal layer and an external hair‐like nap. The nap is formed by a collagen‐like glycoprotein called BclA, while the basal layer contains many different proteins, one of which is a spore‐specific alanine racemase (Alr). In this study, we employed fluorescence microscopy and a fluorescently labelled anti‐Alr monoclonal antibody (mAb) to examine the distribution of Alr within the exosporium. Binding of the mAb occurred over approximately three‐quarters of the exosporium but not in a cap‐like region at one end of the spore, indicating the absence or inaccessibility of Alr in this region. We also determined that the cap‐like region, or cap, corresponds to the first part of the exosporium assembled within the mother cell during sporulation and the only part of the exosporium assembled in a Δ exsY mutant strain of B. anthracis . Our results provide the first direct evidence that exosporium assembly is a non‐uniform process and suggest that exosporium formation is discontinuous. Finally, we demonstrated that during spore germination and outgrowth, the outgrowing cell always escapes from its exosporium shell by popping through the cap, suggesting that the cap is designed to facilitate the emergence of the outgrowing cell.