ABSTRACT
Bacterial cells enhance the proliferation of neighboring cells under stress conditions by emitting a physical signal. Continuous single sine sound waves produced by a speaker at frequencies of 6-10, 18-22, and 28-38 kHz promoted colony formation by Bacillus carboniphilus under non-permissive stress conditions of high KCl concentration and high temperature. Furthermore, sound waves emitted from cells of Bacillus subtilis at frequencies between 8 and 43 kHz with broad peaks at approximately 8.5, 19, 29, and 37 kHz were detected using a sensitive microphone system. The similarity between the frequency of the sound produced by B. subtilis and the frequencies that induced a response in B. carboniphilus and the previously observed growth-promoting effect of B. subtilis cells upon B. carboniphilus through iron barriers, suggest that the detected sound waves function as a growth-regulatory signal between cells.
ABSTRACT
Carbon material such as graphite and activated charcoal, but not diamond, causes the promotion of growth of certain bacteria under ordinarily non-permissive stress conditions over a distance of several centimeters. Bacillus carboniphilus under the stress of a high KCl concentration and high temperature responded to this remote effect of carbon material with enhanced growth, and thermophile bacterium Bacillus stearothermophilus responded similarly yet moderately under the stress of low temperature. The remote effect of carbon was caused by its activation with external energy, probably of electromagnetic nature, as this effect was markedly decreased by sheltering the experimental system with an iron or aluminum barrier. Carbon material probably transforms the external oscillatory pulses or radiation into a signal exerting, far-reaching, growth-promoting effect upon cells. The most plausible candidate of signals emitted from carbon was considered to be (ultra)sonic.
