Heat resistance of bacterial spores correlated with protoplast dehydration, mineralization, and thermal adaptation

Abstract

Twenty-eight types of lysozyme-sensitive spores among seven Bacillus species representative of thermophiles, mesophiles, and psychrophiles were obtained spanning a 3,000-fold range in moist-heat resistance. The resistance within species was altered by demineralization of the native spores to protonated spores and remineralization of the protonated spores to calcified spores and by thermal adaptation at maximum, optimum, and minimum sporulation temperatures. Protoplast wet densities, and thereby protoplast water contents, were obtained by buoyant density sedimentation in Nycodenz gradients (Nyegaard and Co., Oslo, Norway). Increases in mineralization and thermal adaptation caused reductions in protoplast water content between limits of ca. 57 and 28% (wet weight basis), and thereby correlated with increases in sporal heat resistance. Above and below these limits, however, increases in mineralization and thermal adaptation correlated with increases in sporal resistance independently of unchanged protoplast water contents. All three factors evidently contributed to and were necessary for heat resistance of the spores, but dehydration predominated.

Analysis of the role of bacterial endospore cortex structure in resistance properties and demonstration of its conservation amongst species

“…Spore protoplast hydration, measured as core wet density, has been previously associated with heat resistance of spores (Nakashio and Gerhardt 1985;Beaman and Gerhardt 1986). Spores prepared in NB show the lowest wet density (Table 3).…”

Impacts of sporulation temperature, exposure to compost matrix and temperature on survival of Bacillus cereus spores during livestock mortality composting

“…Results of this study are consistent with Collado et al (2006) who theorized that differences in ST for B. cereus altered the germination mechanism of the spores, with sporulation at higher temperatures rendering spores more resistant to germination. In contrast, Gonzalez et al (1999) determined that effects of ST on thermal resistance of spores of B. cereus was strain specific, possibly explaining contradictory studies where thermal resistance of Bacillus spores increased with ST (Beaman and Gerhardt 1986), was inversely related to ST (De Pieri and Ludlow 1992) or was superior at the mid-point of a range of ST (Fernandez-Coll and Rodriguez-Toro 1986).…”

Bacillus sporothermodurans and other highly heat-resistant spore formers in milk

“…It is speculated that mineralization as well as other factors exert their effect indirectly through modulation of the spore core water content. The latter is clearly a major factor determining the spore wet heat resistance, as an inverse correlation has been observed over a wide range of core water contents in spores of different species between core water content and heat resistance (Beaman and Gerhardt 1986). It is thought that reduced water content decreases the amount of water associated with spore proteins, thereby stabilizing these to thermal denaturation.…”