Calcium uptake and survival of Bacillus stearothermophilus

Abstract

The calcium transport in resting vegetative cells of Bacillus stearothermophilus was studied by determining the retention of 45Ca in a membrane filter assay. The kinetics of death by vegetative cells, when suspended in buffer at 55 degrees C, was also investigated. The calcium influx required the presence of an energy source, e.g. glucose-1-phosphate and the system exhibited saturation kinetics. The requirements for survival of the thermophilic cells reflected those of the calcium transport system. Thus, cells treated with nitrogen gas showed an increased thermal stability and a decreased efflux of calcium. The initial velocity of calcium influx correlated linearly with the survival of the cells after 1 min heating at 55 degrees C. Lanthanum inhibited calcium influx and reduced survival. Magnesium did not inhibit calcium influx and could replace calcium as a stabilizing agent. The results suggest that the thermophilic cells are not intrinsically heat stable but survive due to a high cellular concentration of divalent ions.