Further Investigations on the Nature of the Heat Resistance of Thermophilic Bacteria

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Abstract
When cells of Bacillus stearothermophilus, strain NCA 1503, were grown in tryptone starch broth and subsequently transferred to tris buffer, a fraction of the cells: rapidly died in ttie buffer. This fraction increased with increasing content of calcium chloride in the growth medium. The' addition of sodium, potassium or magnesium chloride to the growth medium had no such effect. The rapid dying of the cells in tris buffer was associated with a leakage of organic material and calcium ions from the cells. The results obtained are probably caused by a damage to the osmotic barrier of the cells during their contact with the buffer. Observations: made during the present investigation and a previous one (Ljunger 1970) indicate that the heat resistance of thermophilic bacteria depends on the maintenance of a high intracellular concentration of free calcium ions.

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