Chemical Wave–Electrical Field Interactions in Bacterial Cells

We propose that the extension of diffuse layer and the buildup of electrical field in bacterial cells are important because asymmetric charge distribution and bounded cellular space are the typical subcellular configurations in micron-sized cells. Based on Poisson-Nernst-Planck equations, we provide numerical evidences that the diffuse layer may extend up to 200 nm in dependence of the cation/anion ratio in cellular solution. The effect of negatively-charged nucleoid over intracellular electrical field is discussed and the field strength, at least ~ 15 mV⁄μm in average, is given from simulations. Here, the field configuration in rod-shaped cells are outwardly directed from the nucleoid to the cell membrane. Accordingly, chemical waves, such as Min-protein oscillators in E. coli, traversing across the electrical field built up by intracellular electrolytes are considered to undergo chemical wave–electrical field interactions. Experiments using bacteria expressing Min-protein system is employed to confirm the dispersion relation derived from theory. Frequency modulations can be explained by the dispersion relation and are further verified through the experiments of nucleoid perturbations by either the removal or the morphological changes of the nucleoid due to antibiotic treatments. As revealed from simulations, the field strength altered by the physical schemes for anucleate condition and nucleoid compression and expansion can further modulate the distribution of oscillation frequency as considering the changes of permitted wave modes determined by the dispersion relation ω(k)/ω_c ~ (1-μE∙k+Δk² ), where ω_c is the frequency of the limit-cycle oscillation, μ refers to the electrical mobility and Δ relates to the phase diffusion owing to the reactions. Taken together, the first instability due to direct Coulombic interaction between Min proteins and intracellular electrical field induces the altered composition gradients in wave patterns. Whereas, frequency modulations of Min-protein oscillator is found resulted from the second instability due to the phase diffusion dynamics through the coupling of wave modes and electrical field. The results shown in the current studies depict an indispensable role of wave–field interactions in formation and modulation of bacterial Min-protein oscillator.