Rapid Hyperpolarization of the Cellular Membrane Potential Co-Occurs with Slowed Bacterial Elongation

Background: All cells, including bacteria, maintain an ion gradient across the plasma membrane. The resulting membrane potential is important for cell growth, division, and health. Our current research shows that a subset of Bacillus subtilis ( B. subtilis ) cells exhibit spontaneous, rapid (∼2 min) “spikes” in the membrane potential. The subset of cells that spike increases, and the spikes become more frequent, when cells are exposed to ethanol, an environmental stressor. Our goal is to highlight the association between membrane potential and cell elongation. Methods: To achieve this, membrane potential was measured using tetramethyl rhodamine methyl ester, a voltage-sensing fluorescent dye. Cell fluorescence and elongation were measured simultaneously over a 30-min period using fluorescence and bright field microscopy. Images were analyzed using a combination of ImageJ and custom MATLAB software. Results: We find that the population of cells that spike have slower elongation rates than those with no spikes in both the untreated and ethanol-treated cells over the 30 min of observation.