Ion metabolism in aHalobacterium

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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.

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