Surface architecture of endospores of the Bacillus cereus/anthracis/thuringiensis family at the subnanometer scale

Abstract

Bacteria of the Bacillus cereus family form highly resistant spores, which in the case of the pathogen B. anthracis act as the agents of infection. The outermost layer, the exosporium, enveloping spores of the B. cereus family as well as a number of Clostridia, plays roles in spore adhesion, dissemination, targeting, and germination control. We have analyzed two naturally crystalline layers associated with the exosporium, one representing the "basal" layer to which the outermost spore layer ("hairy nap") is attached, and the other likely representing a subsurface ("parasporal") layer. We have used electron cryomicroscopy at a resolution of 0.8-0.6 nm and circular dichroism spectroscopic measurements to reveal a highly α-helical structure for both layers. The helices are assembled into 2D arrays of "cups" or "crowns." High-resolution atomic force microscopy of the outermost layer showed that the open ends of these cups face the external environment and the highly immunogenic collagen-like fibrils of the hairy nap (BclA) are attached to this surface. Based on our findings, we present a molecular model for the spore surface and propose how this surface can act as a semipermeable barrier and a matrix for binding of molecules involved in defense, germination control, and other interactions of the spore with the environment.electron crystallography | cryoelectron microscopy | two-dimensional crystal

The Exosporium Layer of Bacterial Spores: a Connection to the Environment and the Infected Host

“…Advances in electron microscopic imaging techniques have led to spectacular improvements in our understanding of the exosporium architecture of spores from the B. cereus family (36)(37)(38)(39). The basic structures of the exosporium are similar for B. anthracis, B. cereus, and B. thuringiensis.…”

“…The external face of this structure consists of a series of hexagonally packed concave cups in a honeycomb pattern, with the open ends oriented toward the external environment ( Fig. 2) (38). The spore core-facing side of this structure consists of a honeycomb pattern of hexameric crowns with a diameter of ϳ7.5 to 9 nm (Fig.…”

“…The open ends of the crowns abut one another to form channels between the two faces of the basal layer. The channels have a diameter of ϳ20 to 34 Å (36,38). A channel of this size is cereus family.…”

Sporulation Temperature Reveals a Requirement for CotE in the Assembly of both the Coat and Exosporium Layers of Bacillus cereus Spores

“…The spore peptidoglycan cortex, a structure common to all endospores, is a major factor in the resistance of spores to heat (1,4). The cortex is surrounded by a proteinaceous coat, and in organisms such as Bacillus anthracis or Bacillus cereus the coat is further enveloped by an exosporium, a "balloon-like" structure consisting of a paracrystalline basal layer and an external hair-like nap formed mainly by the collagen-like glycoprotein BclA (5)(6)(7)(8)(9)(10)(11). While the coat contributes to protection against peptidoglycan-breaking enzymes, UV light, and oxidative agents, it is also central to the proper interaction of spores with compounds that trigger germination (10).…”

Complete Genome Sequence of Bacillus cereus Bacteriophage PBC1

“…Although outbreaks caused by B. cereus are relatively infrequent, concerns about B. cereus have not diminished because it is commonly isolated from foods and food additives due to its abilities to form endospores and to grow at a broad range of temperatures (5 to 55°C) (5,9,10,15). With the rapid emergence of antibiotic-resistant bacteria, the use of bacteriophages has regained attention as an efficient alternative method for their control (7,14).…”