Numerical study of the effect of soft layer properties on bacterial electroporation.

We present a numerical model of electroporation in a gram-positive bacterium, which accounts for the presence of a negatively charged soft polyelectrolyte layer (which may include a periplasmic space, peptidoglycan layer, cilia, flagella, and other surface appendages) surrounding its plasma membrane. We model the ion transport within and outside the soft layer using the soft layer electrokinetics-based Poisson-Nernst-Planck formalism. Additionally, we model the electroporation dynamics on the plasma membrane using the pore nucleation-based electroporation formalism developed by Krassowska and Filev. We find that ion transport within the soft layer (surface conduction), which depends on the relative importance of the soft layer charged group concentration compared to the buffer concentration, significantly alters the transmembrane voltage across the plasma membrane and hence the pore characteristics. Our numerical simulations suggest that surface conduction significantly lowers the pore number in the plasma membrane. This observation is consistent with experimental studies that show that gram-positive bacteria, in general, have lower transformation efficiencies compared to gram-negative bacteria. Our studies highlight a strong dependence of bacterial electroporation on cell envelope properties and buffer conditions, which need to be taken into consideration when designing electroporation protocols.