Influence of a Mono-Frequency Sound on Bacteria can be a Function of the Sound-Level

Objectives: To investigate the effect of a mono-frequency (300 Hz) sound on the bacterium Chromobacterium violaceum at different sound levels. Methods: Chromobacterium violaceum was subjected to sonic stimulation with 300 Hz sound, at five different levels of loudness in the range of 70–89.5 dB. Effect of sound treatment was studied on cell yield and pigment production of this bacterium. Findings: Sonic stimulation was found to affect bacterial growth and quorum sensing regulated pigment (violacein) production significantly. Magnitude of this effect was found to be dependent on sound-level. The minimum critical difference required to cause any statistically significant change in bacterial response with respect to sound-level was found to be 13 dB. Growth of C. violaceum was affected more at lower sound intensity, whereas pigment production was affected more at higher sound intensity. Additional experiments with C. violaceum and Serratia marcescens indicated that even a silent speaker emitting no sound can alter bacterial growth and/or pigment production up to a minor extent. Size of the test tube in which bacteria are exposed to sonic stimulation was not found to affect the results much. Application: This study has shown that C. violaceum does respond to sonic stimulation and that the intensity of sound is an important determinant affecting magnitude of this response.