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

Abstract

When cells of Bacillus stearothermophilus, strain NCA 1503, were grown in tryptone starch broth and subsequently transferred to tris buffer, a fraction of tbe celis: rapidly died in the buffer. This fraction increased with increasing content of calciiina chloride in the growth medium. The addition of sodiom, 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 liigh intracellular concentration of free calcium ions.

Calcium uptake byBacillus stearothermophilus: A requirement for thermophilic growth

“…The Arrhenius plot in fig.4 indicates that the Thus calcium appears to be taken up by living calcium uptake rate increases with temperature, in cells at a rate which increases with temperature. In accordance with the higher demand for calcium at the light of earlier results [6,7] that calcium is needed for survival at high temperatures, we conclude that calcium is not just accumulated as a consequence of, but is indeed required for thermophilic growth of B. stearothermophilus.…”

“…In our view, calcium stabilizes the cell functions against the action of heat. The general validity of other theories attempting to explain why thermophilic bacteria are able to grow at high temperatures has been discussed by Ljunger [6,7], and this subject has been reviewed recently [8].…”

The effect of growth rate on the viability of Bacillus stearothermophilus

“…The problem of determining the number of viable cells in a thermophilic culture by plating was first highlighted by Allen [1] who concluded that the method may be expected to give results which are too low because of death of some cells, viable at the time of sampling, before they can develop into colonies. Ljunger [2,3] confirmed that, when cells of Bacillus stearothermophilus grown in broth were transferred to a buffer, a fraction of the cells died rapidly and suggested that an active transport of calcium ions into the cell was needed for viability. Active transport of calcium by B. stearothermophilus was subsequently demonstrated by Stahl [4].…”

Calcium uptake by Bacillus megaterium variants grown at 10° to 65° c

“…Ljunger [1,2] suggested that a high intracellular calcium concentration in cells of thermophilic bacteria is of fundamental importance for their heat stability. Cells of Bacillus stearothermophilus, which is an obligately thermophilic organism, rapidly die at 55°C unless the surrounding medium contains calcium, potassium, phosphate and an energy source [1 ].…”