FIG 5.

Regulation of virulence by extracellular potassium concentration. The virulence of WT bacteria and trkH::Tn5 and trkA::Tn5 mutants was measured by quantification of the mass of macerated tissue 48 h after inoculation of potato tubers. Cells were cultured overnight in LB (approximately 8 mM potassium) and were harvested and resuspended in potassium-free PBS (WT only) or PBS supplemented with a final concentration of either 4.5 mM or 250 mM potassium. Potatoes were inoculated with approximately 3 × 10⁵ cells of the respective strain at the different potassium concentrations. Error bars represent SEM; n = 6; **, P < 0.01; ns, not significant. This is a representative experiment from three independent experiments.