Intracellular concentrations of Na+, K+, and Cl− of a moderately halophilic bacterium

Abstract

The intracellular concentrations of Na+, K+, and Cl− of an unidentified moderately halophilic bacterium were determined. When the cells were grown at a late linear growth phase in a chemically defined medium containing 1, 2, or 3 M NaCl and 5.5 mM K+, the intracellular Na+ concentration (0.90–1.15 M) was independent of the Na+ in the medium. The K+ and Cl− concentrations were roughly on the same levels, respectively (0.67–0.89 M K+; 0.70–0.98 M Cl−). The Na+ and K+ per gram protein of the whole cells were 3.85 mmol and 2.96 mmol, respectively. When the cell envelope was incubated in a 2 M NaCl solution containing 5.5 mM K+ and 0.1 mM Mg2+, the Na+ concentration in the cell envelope was very high (6.49 mmol per gram protein) and K+ was concentrated up to about 41 times of the external K+ (0.36 mmol per gram protein). The high Na+ content of the isolated cell envelope may serve as one of the keys to elucidating a role of Na+ for the maintenance of the cell rigidity in this bacterium.