Protoplast Dehydration Correlated with Heat Resistance of Bacterial Spores

摘要

Water content of the protoplast in situ within the fully hydrated dormant bacterial spore was quantified by use of a spore in a which the complex of coat and outer (pericortex) membrane was genetically defective or chemically removed, as evidenced by susceptibility of the cortex to lysozyme and by permeability of the periprotoplast integument to glucose. We content was determined by equilibrium permeability measurement with Tritium-labeled water (confirmed by gravimetric measurement) for the entire spore, with Carbon 14-labeled glucose for the integument outside the inner (pericytoplasm) membrane, and by the difference for the protoplast. The method was applied to lysozme-sensitive spores of Bacillus stearothermophilus, B. subtilis, B. cereus, B. thuringiensis, and B. megaterium (four types). Comparable Iysozyme-resistant spores, in which the outer membrane functioned as the primary permeability barrier to glucose, were employed as controls. Heat resistances were expressed as D100 values. Protoplast water content of the lyozyme spore types correlated with heat resistance exponentially in two distinct cluster, with the four B. megaterium types in one alignment, and with the four other species types in another. Protoplast water contents of the B. megaterium spore types were sufficiently low to account almost entirely for their lesser heat resistance.