The protonmotive force and alpha-aminoisobutyric acid transport in an obligately alkalophilic bacterium.

Abstract

Measurements of the protonmotive force and studies of solute transport in Bacillus alcalophilus were conducted to ascertain how ceil processes are energized under conditions in which a pH gradient, interior alkaline, cannot be established across the membrane. B. alcalophilus grows on Lmaiate in a range of pH from 9.0 to 11.5, with an optimum at pH 10.5. The electrical potential across the membrane, A+, increases progressively from -84 mV at pH 9.0 to -152 mV at pH 11.5. At pH 10.0 and above a ApH exists, interior acid, increasing from 36 mV at pH 10.0 to 151 mV at pH 11.5. At pH 10.5 and 11, at which growth is excellent, the total transmembrane protonmotive forces were only -80 mV and -15 mV, respectively. Uptake of cu-aminoisobutyric acid (AIB), to concentrations 845-fold greater than the external concentration, occurs only at alkaline pH values, with an optimum at pH 10.5. Saturation kinetics, with a K, for AIB of 9.3 JAM, were