FIG 7.

Cytoplasmic K⁺ content and growth in the free-living state. (A) Cytoplasmic K⁺ content of the indicated strains grown under various K⁺ conditions. Bacterial cells grown for 4 h under 0.05, 0.5, and 5 mM K⁺ conditions were collected, washed with 50 mM NaCl, and then suspended in pure water. These cell suspensions were boiled, and the extracted K⁺ was measured. Total extracted K⁺ was normalized to the OD₅₉₅ of each cell suspension. (B) Growth of the indicated strains under various K⁺ conditions. Each strain was suspended in medium with 0.05, 0.5, and 5 mM K⁺ to an OD₆₀₀ of 0.05 and incubated for 16 h with shaking. After incubation, the OD₅₉₅ of each culture was measured using a 96-well microplate reader. In panels A and B, data are presented as the means ± standard deviations from three replicate cultures.