Sorption of water by spores, heat-killed spores, and vegetative cells

Abstract

Several hypotheses explain the heat resistance of bacterial spores in terms of a hydrophobic nature of the spore surface and possibly also the spore interior. The water-sorption properties of naturally hydrated spores which had never been dehydrated before the experiment were studied. The rate of loss of water over P2O5 at 50 °C was measured in a closed chamber by remote weighing with a Cahn electrobalance. The hygroscopicity expressed as percentage of water bound by the sample at aw = 1, 25 °C was as follows.(I) Chemicals:albumin, 70.5; starch, 42.9.(II) Clostridium botulinum 33A, a heat-resistant strain: spores, 47.0; residue (spores heat killed at 121 °C for 30 min), 50.4; exudate (material released from heat-killed spores) 63.1; vegetative cells, 70.3.(III) C. botulinum, type E, strain Beluga, a heat-sensitive strain: spores 62.5; residue, 61.3; exudate, 77.3.It is postulated that molecular masking in the spore is responsible for low binding of water, electrical and chemical inertness, biological dormancy, and high heat resistance of bacterial spores.