Ion metabolism in aHalobacterium

Abstract

The changes in concentration of K⁺, Na⁺ and Cl⁻ are given in growing cultures of aHalobacterium species subjected to cold, lack of O₂ or starvation. In growing cells, the ion concentration ratios across the cell membrane were 1,000∶1 (inside:outside) for K⁺ and 1∶2 for Na⁺. In bacteria with a low rate of endogenous metabolism induced by 24-hr starvation, the ratios were 500∶1 for K⁺ and 1∶4 for Na⁺. O₂ and a substrate were required for K⁺ uptake in growing bacteria, but not for the maintenance of K⁺ and Na⁺ gradients in starving bacteria. The exchange of K⁺, Na⁺ and Li⁺ across the cell membrane of starving bacteria was found to have a time constant for 50% completion of the process of 20 to 30 sec. The exchange of cell Cl⁻ with NO ₃ ⁻ was a twostage process with time constants of approximately 2 min and 2–1/2 hr. The results are explained in terms of the binding of most of the cell K⁺ which brings about the distribution of Na⁺ and Cl⁻ according to the Gibbs-Donnan equilibrium; the role of metabolism is to induce changes in the mean ion-activity coefficients.