FIG 4.

Growth of B. subtilis potassium transporter mutants at different potassium concentrations in the presence of ammonium or glutamate. B. subtilis mutants expressing one of the transmembrane subunits KtrB and KtrD or the hybrid channels KtrCB and KtrAD as the single potassium uptake system were cultivated in MSSM medium with 50 mM KCl and ammonium. Cells were harvested and washed, and the OD₆₀₀ was adjusted to 1.0. Serial dilutions were added dropwise to MSSM plates with the indicated potassium concentration and ammonium or glutamate.