Phosphate transport in Halobacterium halobium depends on cellular ATP levels

Freshly harvested Halobacterium halobium cells grown in the presence of 0.5 mM Pi took up phosphate with a low apparent Km. Import depended on intracellular ATP levels; sodium and proton (electro)chemical gradients alone were not competent to drive Pi uptake. Although most of the phosphate accumulated as Pi in the cells, efflux of Pi was difficult to achieve.