Electrically induced bacterial membrane potential dynamics correspond to cellular proliferation capacity

Abstract

11Membrane-potential dynamics mediate bacterial electrical signaling at both intra-and inter-cellular 12 levels. Membrane potential is also central to cellular proliferation. It is unclear whether the cellular 13 response to external electrical stimuli is influenced by the cell's proliferative capacity. A new strategy 14 enabling electrical stimulation of bacteria with simultaneous monitoring of single-cell membrane 15 potential dynamics would allow bridging this knowledge gap and further extend electrophysiological 16 studies into the field of microbiology. Here we report that an identical electrical stimulus can cause 17 opposite polarization dynamics depending on cellular proliferation capacity. This was demonstrated 18using two model organisms, namely B. subtilis and E. coli, and by developing an apparatus enabling 19exogenous electrical stimulation and single-cell time-lapse microscopy. Using this bespoke apparatus, we 20show that a 2.5 sec electrical stimulation causes hyperpolarization in unperturbed cells. Measurements 21 of intracellular K + and the deletion of the K + channel suggested that the hyperpolarization response is 22caused by the K + efflux through the channel. When cells are pre-exposed to UV-violet light, the same 23 electrical stimulation depolarizes cells instead of causing hyperpolarization. A mathematical model 24 extended from the FitzHugh-Nagumo neuron model suggested that the opposite response dynamics are 25 due to the shift in resting membrane potential. As predicted by the model, electrical stimulation only 26induced depolarization when cells are treated with antibiotics, protonophore or alcohol. Therefore, 27electrically induced membrane potential dynamics offer a novel and reliable approach for rapid detection 28 of proliferative bacteria and determination of their sensitivity to antimicrobial agents at the single-cell 29 level. 30 31

The Microbiologist’s Guide to Membrane Potential Dynamics

“…This suggests that electrical signaling and metabolism are tightly coupled in bacteria. Consistent with this observation, our group showed in a recent study that electrical stimulation induces opposite responses in proliferative and inhibited cells [64]. When scaled up to the level of a biofilm, electrical signaling is indeed coupled with metabolic activity [49].…”

“…The dynamic response of membrane potential to stimuli is inherently linked to cellular capacity to proliferate because of its function as a free energy source. Using a bespoke experimental tool, Stratford et al showed that actively proliferating cells and growth-inhibited cells respond to an electrical stimulation in apparent opposite directions [64]. A phenomenological mathematical model, based on the FitzHugh-Nagumo neuron model [65], provided a mechanistic understanding of the observed response dynamics.…”

“…Accordingly, membrane potential can be determined by measuring the ratio between the fluorescence intensities inside and outside the cell. Lipophilic fluorescent cationic dyes, such as tetramethylrhodamine, methyl ester (TMRM), have been used to probe bacterial membrane potential [11,12,59,64,90,91]. Nernstian dyes present a particularly powerful and convenient tool for microbiological investigations, although their use for quantitative biophysical investigations requires more careful calibrations [91,92].…”

Electrochemical communication in biofilm of bacterial community

“…In recent years, bacterial electrophysiology has been demonstrated to have important roles in the various physiological processes like cellular proliferation, electrochemical communication, persister cell formation, and antibiotic resistance [49][50][51][52]. Electrochemical signaling via K + channels, together with resultant membrane potential, which is specific for different bacterial communities, is a way of electrochemical communication in bacterial biofilm.…”

TrkA undergoes a tetramer-to-dimer conversion to open TrkH which enables changes in membrane potential

“…While the physiological roles of many eukaryotic cation channels have been well characterized, the roles of cation channels in bacterial physiology are much less clear. Recent studies have established a role for K + channels in membrane potential changes in Bacillus subtilis 20,21 and Corynebacterium glutamicum 22 . However, the precise cellular function of bacterial SKTs, some of which are not stringently selective for K + , has not yet been determined.…”