Influence of divalent cations on the growth and morphology of Bacillus stearothermophilus

Abstract

Bacillus stearothermophilus grows within the temperature range 40-70°C in a complex medium that contains 115 μM-Ca2+ and 95 μM-Mg2+. The addition of Ca2+ to a final concentration ranging from 2.5 to 10 mM stimulated growth at suboptimal and supraoptimal temperatures, extending growth above 70°C, but had no effect on growth within the optimal temperature range. Mg2+ (2.5 mM) also stimulated growth although to a lesser extent. Furthermore, 10 mM-Mg2+ inhibited growth at temperatures higher than 65°C. This inhibitory effect was relieved by the addition of 2.5 mM-Ca2+. Sr2+ (10 mM), which often behaves as a Ca2+ analogue in biological systems strongly inhibited growth and produced gross morphological alterations in the cells. The inhibitory effect of Sr2+ could also be relieved by addition of Ca2+.