FIGURE 4.

Dependence of strain growth on K⁺ concentration. Strains were grown under AmtB-expressing conditions (Na⁺-based N⁻C⁻ minimal medium containing 0.4% glucose, and 3 mm glutamine) in medium supplemented with varying concentrations of KCl (0.5 mm (♢), 1 mm (▵), 2 mm (○), 5 mm (□), 10 mm (♦), 20 mm (▴), 50 mm (●), and 100 mm (■)). Growth medium isotonicity was maintained by the addition of NaCl such that the total KCl/NaCl supplement equaled 100 mm. All amtB alleles were carried in the kdp trk kup strain background. The data, from a single experiment, are representative of findings made in three independent trials.