Thermally induced leakage of cellular material and viability in <i>Vibrio marinus</i>, a psychrophilic marine bacterium

Abstract

Vibrio marinus MP-1, an obligate psychrophilic marine bacterium, was severely damaged when heat-shocked in growth medium. Cells heat-shocked at 20, 23, and 25 C in growth medium released 260 mμ absorbing material (nucleic acids and nucleotides), orcinol-reacting material (RNA), ninhydrin-reacting material (amino acids), malic dehydrogenase, and glucose-6-phosphate dehydrogenase increasingly at higher temperatures. Older cultures were found to be more resistant to thermal death, lysis, and leakage. No significant leakage or lysis could be detected after the heat-shocking of stationary phase cells in growth medium for 120 min when more than 99.9% were killed. Cells in the log phase of growth were the most sensitive to death, leakage, and lysis. After 95% were killed at 25 C, and 94% at 20 C, cells began to release intracellular materials. Leakage and lysis occurred concomitantly after death. Loss of membrane permeability control before death would, therefore, not be indicated. It is suggested that the increased sensitivity to heat in young cultures may be attributed to thermolabile synthetic mechanisms involved in rapidly growing cultures.