Inhibition of Bacillus subtilis spore germination by various hydrophobic compounds: demonstration of hydrophobic character of the L-alanine receptor site

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Abstract
L-Alanine-initiated germination of B. subtilis spores was inhibited by various kinds of hydrophobic compounds. Good correlation of inhibitory effect with hydrophobicity of the compound was demonstrated by using regression analysis in which the hydrophobic character was expressed by the partition coefficient in an octyl alcohol-water system. The correlation coefficient for 20 alcohols was 0.959, and that for 19 miscellaneous compounds was 0.906. Regression lines of the alcohols and other hydrophobic compounds were almost identical, showing that hydrophobic interaction played an important role in inhibition. Diphenylamine was 1 of the most effective inhibitors examined. n-Octyl, n-nonyl and n-decyl alcohols were the most effective alcohols. The mode of inhibition by diphenylamine and n-octyl alcohol was a mixed type (competitive plus noncompetitive type) with respect to L-alanine; that by D-alanine was competitive inhibition. Sites for diphenylamine, n-octyl alcohol and D-alanine may have overlapped. Inhibition was reversible by washing; heat resistance, stainability and germination rate of the washed spores remained unaltered. Inhibition may occur before the initial trigger reaction of germination and it may be due to the interaction between a hydrophobic compound and a hydrophobic region closely associated with the L-alanine receptor site on the spore.

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