Eugenol induced inhibition of extracellular enzyme production by Bacillus subtilis

Eugenol, the major essential oil of clove, in sublethal concentrations (0.02-0.03%, v/v) inhibited the production of alpha-amylase, protease, and subtilisin by Bacillus subtilis in laboratory media. Microscopic observations revealed that at these eugenol concentrations, B. subtilis cells appeared swollen and distorted and/or appeared as very long and thin filaments (> 100 μm). Of 20 amino acids investigated, only L-glutamic or L-aspartic acid (>5.0 mg/ml) prevented such morphogenic distortions when added to eugenol-containing media before inoculation. Addition of these amino acids also resulted in an increase in biomass and protease production. In contrast, the addition of serine (> 1.0 mg/ml) enhanced filamentous growth but reduced the production of protease and subtilisin.