FIG 8.

(A) Estimation of intracellular K⁺ content in S. mutans wild-type UA159 strain and K⁺ transport knockout mutants. To deplete cells of K⁺ prior to uptake assays, mid-exponential-phase cells were incubated in K⁺-deficient MMGK growth medium for 2 h. Cells were then supplemented with 10 mM KCl, and aliquots were sampled over time to measure intracellular K⁺ content using ICP-OES. Values are means ± standard deviations for at least four biological and two technical replicates. Repeated-measures ANOVA was performed, and comparisons were made between different time points within each group (*) and by comparing intracellular K⁺ levels between groups (#); a P value of <0.05 is considered significant. (B) Intracellular K⁺ accumulation after 30 min. Wild-type UA159 and knockout mutant strains were grown to an OD₆₀₀ of ∼0.4 in THYE medium prior to incubation in minimal medium for 10 to 12 h to deplete cellular K⁺. Cells were subsequently challenged with 25 mM K⁺ for 30 min followed by measurement of cellular cation content via ICP-OES. Values are means and SE; experiments were repeated at least four times, and statistical comparison was performed using a two-way ANOVA. *, P < 0.01 compared to the value for WT cells stimulated with 25 mM K⁺; #, P < 0.01 compared to the value for WT cells starved of K⁺.