The high-resolution architecture and structural dynamics of Bacillus spores

¹ Lawrence Livermore National Laboratory
² Children's Hospital Oakland Research Institute

^* To whom correspondence should be addressed. E-mail: malkin1{at}llnl.gov.

Submitted on July 9, 2004
Revised on September 10, 2004
Accepted on 13 October 2004

	Abstract

The capability to image single microbial cell surfaces at nanometer scale under native conditions would profoundly impact mechanistic and structural studies of pathogenesis, immunobiology, environmental resistance and biotransformation. Here, using in vitro atomic force microscopy (AFM), we have directly visualized high-resolution native structures of bacterial endospores, including the exosporium and spore coats of four Bacillus species in air and water environments. Our results demonstrate that the mechanisms of spore coat self-assembly are similar to those described for inorganic and macromolecular crystallization. The dimensions of individual Bacillus atrophaeus spores decrease reversibly by 12% in response to a change in the environment from aqueous to aerial phase, establishing that the dormant spore is a dynamic physical structure. The interspecies distributions of spore length and width were determined for four species of Bacillus spores in water and air environments. The dimensions of individual spores differ significantly depending upon species, growth regimes and environmental conditions. These findings may be useful in the reconstruction of environmental and preparation conditions during spore formation and for modeling the inhalation and dispersal of spores. This study provides a direct insight into molecular architecture and structural variability of bacterial endospores as a function of spatial, temporal and developmental organizational scales.

Key Words: atomic force microscopy, bacterial spores, exosporium, spore coat, spore dynamics, spore size distribution

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