Internal cation concentrations of the halotolerant bacterium Brevibacterium sp. were investigated, with the cells grown in a complex media supplemented with nine kinds of salts. With increases in the external NaCI concentration, the amount of Na+ ion in the cells increased, while the intracellular concentration of the K+ ion remained almost constant (about 300 mM). The same tendency was observed when NaCI was replaced with KCI, although the Na+ ion was very low (about 15 mM). On the contrary,

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... tracellular concentrations of Mg2+ and Ca2+ decreased slightly with the increase in NaCI or KCI concentrations in the medium. When the RbCI concentration in the medium was increased to more than 100 mM, Rb + ions in the cells increased about one hundred times, 550-600 mM, while K+ ions decreased to one-tenth. The same experiment was resumed using the chemically defined medium. We observed two different phenomena. First, the intracellular Na+ content (about 200 mM) was more than ten-fold higher than that of the cells grown in the complex medium. Second, the release of K+ ions from the cells at alkaline pH was not as remarkable as that in the complex medium. The release of K+ ions observed in the complex medium was correlated with the addition of 50 mM diethanolamine-hydrochloride for adjusting medium pH at 9.0. Na+ H+ Concerning the energetic systems -rich environments and require Na+ antiporter via H+ pump (3, 13, 16)