  Information processing in the mammalian brain relies on a careful regulation
of the membrane potential dynamics of its constituent neurons, which propagates
across the neuronal tissue via electrical signalling. We recently reported the
existence of electrical signalling in a much simpler organism, the bacterium
Bacillus subtilis. In dense bacterial communities known as biofilms,
nutrient-deprived B. subtilis cells in the interior of the colony use
electrical communication to transmit stress signals to the periphery, which
interfere with the growth of peripheral cells and reduce nutrient consumption,
thereby relieving stress from the interior. Here we explicitly address the
interplay between metabolism and electrophysiology in bacterial biofilms, by
introducing a spatially-extended mathematical model that combines the metabolic
and electrical components of the phenomenon in a discretised reaction-diffusion
scheme. The model is experimentally validated by environmental and genetic
perturbations, and confirms that metabolic stress is transmitted through the
bacterial population via a potassium wave. Interestingly, this behaviour is
reminiscent of cortical spreading depression in the brain, characterised by a
wave of electrical activity mediated by potassium diffusion that has been
linked to various neurological disorders, calling for future studies on the
evolutionary link between the two phenomena.
