Resistant Bacterial Spore Coats and Their Breakdown During Germination

摘要

The bacterial endospore is a uniquely resistant and highly differentiated form of bacterial cell. Its unique structure confers resistance to a variety of conditions such as heat, pressure, radiation, dehydration and chemicals. Nevertheless, it is able to respond rapidly to an appropriate chemical stimulus, undergoing biophysical and degradative changes that remove the specialized layers of coat and cortex, and restore the activities of a vegetative cell. Two major proteases of broad specificity have been detected in spore coat layers. One, AprX, is released into the supernatant during germination, both in a free form and associated with high molecular weight complexes. The second, a 30kDa protease, is retained in the spore. Mutant spores lacking AprX overproduce the 30kDa protease, possibly in a compensatory manner. These proteases of broad specificity are likely to be involved in the breakdown of spore coat proteins during germination. A strain with an unusually alkali-resistant spore coat was identified as Brevibacillus borstelensis. Coat proteins were successfully extracted by boiling at neutral pH with high concentrations of reducing agent and detergent. This strain germinated very slowly and asynchronously, making it impractical to undertake biochemical studies of spore germination or coat degradation.