Morphogenesis of the Bacillus anthracis spore.

摘要

With the ability to shut down metabolism, survive exposure to high degrees of heat, ultra-violet and ionizing radiation, digestive enzymes, and antimicrobials, the bacterial spore is one of the most-resistant forms of life on earth. Although most spores are harmless, several species' spores cause serious diseases such as tetanus, anthrax, gas gangrene, botulism, and diarrhea. Spore-forming bacteria differentiate into spores in response to stresses (especially starvation) in a multi-stage developmental pathway involving the coordinated expression of hundreds of genes and the formation of specialized protective organelles which surround and protect the spore during dormancy. The Bacillus anthracis spore (the causative agent of anthrax) has three of these protective structures: a specialized peptidoglycan called the cortex, a proteinaceous coat and (flexible) exosporium, the latter of which is studded with collagen-like fibers made up of both proteins and glycoproteins. About 80 proteins make up the coat and exosporium. Only about nine or ten of these proteins control the deposition and assembly of all the others into these highly-organized organelles. These so-called morphogenetic proteins are highly conserved and were first identified in the model spore forming organism Bacillus subtilis where they are responsible for organizing the assembly of the coat. To better understand the role that these proteins play in forming the unique architecture of the coat and exosporium in B. anthracis my colleagues and I disrupted five homologues of morphogenetic protein genes and analyzed their role in forming spore structures. These analyses suggest that morphogenetic proteins responsible for the formation of the outer-most structures evolve to form novel surface architectures, possibly allowing each species' spore to take on new functions, and may allow them to occupy novel environmental niches.