Measurements of net fluxes and extracellular changes of H+, Ca2+, K+, and NH4+ in Escherichia coli using ion-selective microelectrodes

This study introduced the use of a non-invasive ion-selective microelectrod e (MIFE) technique to study membrane-transport processes in bacteria. Net i on fluxes and changes in the extracellular concentrations of H+, Ca2+, K+ a nd NH4+ in adherent bacteria, isolated from cultures at different growth st ages (exponential, late exponential, and stationary phases), were monitored . With the exception of Ca2+, a significant (P = 0.05) difference was found in the magnitude of net fluxes of the ions measured from bacterial cells a t different stages of the population growth curve. The magnitude of the Hresponse was glucose-dependent with maximum changes occurring at the highes t concentration. There was a progressive increase in H+ extrusion followed by a gradual return to zero at late stationary phase. Measurements of net i on fluxes crossing the bacterial cytoplasmic membrane, demonstrated here fo r the first time, may offer insight into underlying mechanisms of ion trans port kinetics. Applications of the non-invasive ion-selective microelectrod e technique in microbiology are discussed. (C) 2001 Elsevier Science B.V. A ll rights reserved.