Figure 2.

Growth curves of the Gram-positive bacteria Bacillus megaterium VKM41 and Micrococcus luteus B1314 strains in the presence of Lchα, Lchα/Lchβ mixture (1:1), and the β-hairpin peptide AA139. The concentrations used (1–6): Lchα—2.5, 5, 10, 20, 30, and 40 μg/mL; Lchα + Lchβ—0.19, 0.38, 0.75, 1.5, 3, and 6 μg/mL (total concentration); AA139—0.16, 0.31, 0.63, 1.25, 2.5, and 5 μg/mL. Control—the growth curves of the cultures without the peptides. Red, orange, and blue lines correspond to the growth curves of the cultures in half Mueller–Hinton (½ MH) medium without salts and with the addition of 1.25 mM MgCl₂ or 1.25 mM CaCl₂, respectively. Error bars represent standard deviation between technical replicates. The most pronounced increase in the Lchα antimicrobial activity in the presence of Ca²⁺ was observed at the peptide concentration of 30 μg/mL ≅ 9 μM (enclosed in frame; differences in mean A values between the wells without salts and with the addition of 1.25 mM CaCl₂ were compared by t-test (significance level is * p < 0.05)).