SUMMARY: Phenols are able to lower the temperature of heat activation (breaking of dormancy by heat shock) in spores. The effect was observed with a series of phenols ranging, according to increasing lipophilic character, from unsubstituted phenol to 2,4-dichlorophenol. However, the concentration required to produce the same effect with each phenol was reduced with increasing apolar character. A linear relationship was obtained between the log of the concentration of each phenol needed to produce a 4 °C shift of the half-activation temperature and the log of its octanol/water partition coefficient. In contrast, the isopropyl-substituted phenols thymol, 2- and 4-isopropylphenol and 3-isopropylcatechol all raised the half-activation temperature of the spores. The same effect was observed with menthol, the unsaturated analogue of thymol. The heat resistance of the spores was lowered by all phenols, including isopropyl-substituted phenols. Although the reason for the anomalous behaviour of isopropyl-substituted phenols is not known, the opposite effect on spore heat activation and spore heat resistance indicates that the activation process of the spores is not linked to the process of spore killing. Therefore, spore activation is not due to some kind of non-specific sublethal protein denaturation, as might have been concluded previously from the fact that many spore activation methods are sublethal treatments.


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