Calmodulin antagonists inhibit germination of Bacillus cereus T spores

Abstract

The effects of two calmodulin antagonists, trifluoperazine (TFP) and N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalene sulphonamide hydrochloride (W‐7) on L‐alanine‐induced germination of Bacillus cereus T spores were examined by measuring commitment to germination, decrease in optical density at 660 nm and phase‐contrast microscopy. The kinetics of optical density decrease suggested competitive inhibition of TFP or W‐7 with both L‐alanine and D‐alanine (L‐alanine analogue and germination inhibitor) as determined by Lineweaver‐Burk and Schild plots, respectively. Germination inhibition was pH‐dependent. The I50 values for maximum decreasing rate of optical density in 10 mmol/l L‐alanine plus 5 mmol/l adenosine at pH 6·4 were 0·21 and 0·74 mmol/l for TFP and W‐7, respectively. Much less effect of N‐(6‐aminohexyl)‐l‐naphthalene sulphonamide hydrochloride than W‐7 lends support to the specificity of W‐7. The calmodulin antagonists were effective at a step in germination after commitment and loss of heat resistance. It is postulated that this process is necessary in the germination of B. cereus T spores to convert phase‐bright spores to phase‐dark spores and to cause a decrease in optical density.