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Bacterial spores are robust and dormant life forms with formidable resistance properties, in part, attributable to the multiple layers of protein that encase the spore in a protective and flexible shield. The coat has a number of features pertinent to the emerging field of nanobiotechnology including self-assembling protomers and the capacity for engineering and delivery of foreign molecules. This review gives an account of recent progress describing the use of the spore, and specifically, the spore coat as a vehicle for heterologous antigen presentation and protective immunization (vaccination). As interest in the spore coat increases it seems likely that they will be exploited further for drug and enzyme delivery as well as a source of novel self-assembling proteins.

SpoIVB is essential for intercompartmental signalling in the sigma(K)-checkpoint of Bacillus subtilis. SpoIVB is synthesized in the spore chamber and is the signal which activates proteolytic processing of pro-sigma(K) to its mature and active form sigma(K). We show here that SpoIVB is a serine peptidase of the SA clan. Expression of SpoIVB in Escherichia coli has shown that SpoIVB is able to self-cleave into at least three discrete products, and in vitro studies have shown cleavage in trans. Autoproteolysis of SpoIVB is tightly linked to the initiation of the two developmental functions of this protein, signalling of pro-sigma(K) processing and a yet, uncharacterized, second function which is essential for the formation of heat-resistant spores. In B. subtilis, SpoIVB is synthesized as a zymogen and is subject to two levels of proteolysis. First, autoproteolysis generating intermediate products, at least one of which is proposed to be the active form, followed by processing by one or more enzymes to smaller species. This could provide a mechanism for switching off the active SpoIVB intermediate(s) and suggests a similarity to other proteolytic cascades such as those found in blood coagulation.

The expression of the Bacillus subtilis spoIVB gene, which encodes a developmental cell-cell signalling molecule, has been characterized. In some conditions, this gene can be transcribed by RNA polymerase associated with either sigma F or sigma G, in contrast to previous studies implying exclusive control by sigma G. However, during sporulation, only sigma G directs significant levels of spoIVB expression.

Our understanding of the genetics and physiology of the spore-forming genus Bacillus is remarkable. On the other hand, though, where these Gram-positive bacteria live and grow is far from clear. The soil, once considered their habitat, may simply serve as a reservoir. A growing number of studies show that Bacillus spores can be found in the intestinal tracts of animals, raising the question of whether this could be where they live and grow. In this study, we have conducted the first evaluation of Bacillus spore formers in soil and in human faeces. Our aim is simply to determine the abundance of aerobic spore-formers. Our results show that soil carries approximately approximately 10(6)spores/g while human faeces an average of up to 10(4)spores/g. The numbers of spores found in faeces, we reason, is too high to be accounted for principally by ingestion of food contaminated with spores from soil. This provides further evidence that Bacillus spore formers may have adapted to survival within the intestinal tract of insects and other animals that ingest them; if so they may well be hitherto undiscovered gut commensals.