A novel spore protein, ExsM, regulates formation of the exosporium in Bacillus cereus and Bacillus anthracis and affects spore size and shape.
Bacillus cereus spores are assembled with a series of concentric layers that protect them from a wide range of environmental stresses. The outermost layer, or exosporium, is a bag-like structure that interacts with the environment and is composed of more than 20 proteins and glycoproteins. Here, we identified a new spore protein, ExsM, from a beta-mercaptoethanol extract of B. cereus ATCC 4342 spores. Subcellular localization of an ExsM-green fluorescent protein (GFP) protein revealed a dynamic pattern of fluorescence that follows the site of formation of the exosporium around the forespore. Under scanning electron microscopy, exsM null mutant spores were smaller and rounder than wild-type spores, which had an extended exosporium (spore length for the wt, 2.40 +/- 0.56 microm, versus that for the exsM mutant, 1.66 +/- 0.38 microm [P < 0.001]). Thin-section electron microscopy revealed that exsM mutant spores were encased by a double-layer exosporium, both layers of which were composed of a basal layer and a hair-like nap. Mutant exsM spores were more resistant to lysozyme treatment and germinated with higher efficiency than wild-type spores, and they had a delay in outgrowth. Insertional mutagenesis of exsM in Bacillus anthracis DeltaSterne resulted in a partial second exosporium and in smaller spores. In all, these findings suggest that ExsM plays a critical role in the formation of the exosporium.
Fazzini
Monica M
MM
Laboratory of Bacterial Pathogenesis and Immunology, the Rockefeller University, New York, New York 10065, USA.
Schuch
Raymond
R
Fischetti
Vincent A
VA
D001408:Bacillus anthracis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D001409:Bacillus cereus / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D009154:Mutation; D013171:Spores, Bacterial / Q000502:physiology / Q000648:ultrastructure
D001426:Bacterial Proteins