Heat Shock Proteins Do Not Influence Wet Heat Resistance of Bacillus subtilis Spores

Abstract

Spores of Bacillus subtilis are significantly more resistant to wet heat than are their vegetative cell counterparts. Analysis of the effects of mutations in and the expression of fusions of a coding gene for a thermostable ␤-galactosidase to a number of heat shock genes has shown that heat shock proteins play no significant role in the wet heat resistance of B. subtilis spores.The gram-positive bacterium Bacillus subtilis undergoes the process of sporulation when nutrients become exhausted, and the resulting spores are more resistant than are the growing cells to a variety of environmental insults including heat, UV and gamma radiation, and a number of toxic chemicals (8,34). Wet heat resistance is probably the most dramatic resistance property of dormant spores, as spores are resistant to about 40°C-higher temperatures than are vegetative cells (8). Spore wet heat resistance is due to a number of factors including dehydration of the spore protoplast or core (8), mineralization of the spore core (8), saturation of spore DNA with ␣/␤-type small acid-soluble proteins (33, 34), and thermal adaptation, as spores of a single species formed at higher temperatures are more wet heat resistant than are spores formed at lower temperatures (8, 39).Although many factors contribute to spore wet heat resistance, the identity of the target for wet heat killing of spores is not known. However, two different types of studies have indicated that spore DNA is not the killing target and suggested that some spore protein might be the target (2, 7, 30). If spore killing by wet heat is indeed through protein damage, then it is possible that repair or removal of a damaged protein might be important in spore wet heat resistance. Proteins that can repair or remove denatured proteins in vivo are often members of the heat shock regulon, which is important in the survival of many different bacteria after a heat shock (9,17). Since sporulation at elevated temperatures results in spores with increased heat resistance and heat shock protein synthesis is increased at elevated temperatures (12, 38), then spores prepared at higher temperatures may also have increased levels of heat shock proteins which may in turn contribute to their increased heat resistance. In order to investigate whether proteins of the heat shock regulon play any role in wet heat resistance of B. subtilis spores, we have examined (i) the effect of mutations in known heat shock genes on spore wet heat resistance, (ii) the effect of mild heat shock at various times during sporulation on spore wet heat resistance, and (iii) the expression of heat shock genes during germination of spore populations which had been killed ϳ50% by wet heat treatment.Effects of mutations in heat shock genes on spore wet heat resistance. The heat shock genes of B. subtilis are grouped into at least three classes based on the precise mechanism for the regulation of their expression (11); we examined the effects of mutations in representatives from each of the three classes. Mutations in class I genes...

Spores of Bacillus subtilis: their resistance to and killing by radiation, heat and chemicals

“…However, the higher intrinsic thermostability of macromolecules, in particular proteins, from thermophiles also likely contributes to the increased wet heat resistance of their spores. In contrast to the situation in growing cells, heat shock proteins play no role in the wet resistance of spores (Melly and Setlow 2001).…”

The effect of acid shock on sporulating Bacillus subtilis cells

“…In this study, KatA disappeared 2 h after acid shock was applied. It has also been shown that heat‐shock proteins do not directly influence wet heat resistance of B. subtilis spores, since analysis of the effects of mutations of heat‐shock genes did not produce differences in spore heat resistance (Melly and Setlow 2001).…”

“…In this study, KatA disappeared 2 h after acid shock was applied. It has also been shown that heat-shock proteins do not directly influence wet heat resistance of B. subtilis spores, since analysis of the effects of mutations of heat-shock genes did not produce differences in spore heat resistance (Melly and Setlow 2001). It is possible that sporulation was delayed by 1 h as a result of the 30 min of acid shock, but it is also possible that the induction of stress proteins for 30 min was responsible for the delay.…”

Photocatalytic inactivation of spores of Bacillus anthracis using titania nanomaterials

“…Heat treatment, UV, and ␥ radiation also exhibited promising decontamination properties against spores of Bacillus species. These reports have also indicated that, B. thuringiensis and B. anthracis Sterne along with B. cereus form a better group of surrogates for virulent B. anthracis [19][20][21][22][23].…”