Bacillus carboniphilus cells respond to growth-promoting physical signals from cells of homologous and heterologous bacteria.

Bacillus carboniphilus strains under the ordinarily non-permissive stress of high KCl concentrations and high-temperature conditions are very sensitive recipients of growth-promoting signals from both homologous and heterologous bacterial cells. These signals are not due to a volatile chemical substance, but are of a physical nature, very probably sonic, since they can be transmitted from one Petri dish to another even through a 2mm iron barrier.