FIG 4 .

Positively charged amino acids can partially compensate for the lack of potassium in the medium. (A) Growth assay of B. subtilis 168 in the presence of 0.1 mM KCl and 0.1 mM KCl with the addition of ornithine, citrulline, and arginine (15 mM each). The y axis shows time (t) (in hours). As a control, the wild type was grown in the presence of 5 mM KCl (black) (n = 3). (B) Growth assay of B. subtilis 168 in the absence of potassium (white) and in the absence of potassium with the addition of ornithine, glutamate, citrulline, arginine, lysine, isoleucine, and alanine (15 mM each) (n = 3). (C) B. subtilis 168 was grown at 5 mM KCl, 0.1 mM KCl with and without the addition of ornithine (15 mM), and without external potassium with the addition of ornithine (15 mM). The cellular K⁺ concentrations were determined by ICP-OES. Circles represent the values for biologically independent replicates, and the short horizontal bars indicate the mean values of the replicates (n = 3 for 5 mM KCl; n = 6 for all other conditions).