Electrophysiological functions of microbes

Abstract

Akin to neurons, all microbes maintain an electric potential (a.k.a. membrane voltage) across their membranes. The exact function and generation mechanism of microbial membrane voltage remains elusive. Microbes also maintain close to neutral intracellular pH and Ion Motive Forces, the most relevant of which is the Proton Motive Force (an electrochemical gradient of protons across the membrane).

In this thesis, I propose a thermodynamically consistent framework for modelling cellular electrophysiology, and based on the models I propose that in bacteria \textit{(i)} one important function of membrane voltage is to allow simultaneous maintenance of intracellular pH and PMF in environments bearing different extracellular pH and \textit{(ii)} proton:ion antiporters are responsible for membrane voltage maintenance. Single-cell measurements of PMF and intracellular pH in \textit{E. coli} support the main prediction of my model predictions, namely that the ability to maintain intracellular pH or membrane voltage is PMF dependent. I then evaluate in silico the energetic cost of maintaining intracellular pH and PMF in environments with different ionic composition and make predictions on how the growth-rate and growth-yield are expected to change upon ionic perturbations of the growth medium. I conclude by introducing an approach for the analysis of electrophysiological behaviors that I think is more intuitive and generic than the current teaching practices.