Protonmotive force in Brevibacterium flavum: the lack of intracellular pH homeostasis

Abstract

Brevibacterium flavum 22LD-P cells were shown to maintain a transmembrane pH gradient (ΔpH) from 0.6 to 1.8–2 units and a transmembrane electric potential difference (ΔΨ) from 0 to 200 mV depending on the pH and ionic composition of the incubation medium, grwoth substrate and concentration of cells. ΔΨ decreased from 120–140 mV to 0 when medium pH was lowered from neutral to 5.0–5.5 and increased to 180–200 mV when medium pH was raised to 8–9 in cells utilizing acetate or endogenous substrate. Cells growing on sucrose, kept ΔΨ around 100–120 mV at neutral as well as acidic medium pH. Intracellular pH in the acetate utilizing or endogenously respiring cells was maintained with the range of 8.9 to 5.5 at medium pH ranging from 9.1 to 4.0, respectively. Sucrose grown cells were able to maintain a more stable intracellular pH. Endogenously respiring cells in potassium phosphate buffer at high biomass concentrations maintained larger ΔpH and relatively smaller ΔΨ, than the same cells in diluted suspensions. Cells in sodium phosphate buffer possessed larger ΔΨ and almost no ΔpH, but ΔΨ was still dependent on biomass concentration.