Interactions of Galleria mellonella Proline-Rich Antimicrobial Peptides with Gram-Negative and Gram-Positive Bacteria

Two proline-rich antimicrobial peptides (PrAMPs), named P1 and P2, purified from hemolymph of the greater wax moth <i>Galleria mellonella</i>, were studied for their effects on Gram-negative (<i>Escherichia coli</i>) and Gram-positive (<i>Micrococcus luteus</i>) bacteria. Both peptides decreased the <i>M. luteus</i> bacterial survival rate and caused <i>E. coli</i> bacterial membrane permeabilization. However, in both cases, the P2 peptide was approximately three times more effective than the P1 peptide. Fluorescence microscopy imaging demonstrated binding of both FITC-labeled peptides to <i>E. coli</i> and <i>M. luteus</i> cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging of peptide-treated bacteria revealed considerable changes in cell morphology, cell surface topography, and nanomechanical properties. The interactions of the PrAMPs with bacterial cells were also analyzed by FTIR spectroscopy. The P1 peptide action toward <i>E. coli</i> led to partial aggregation of proteins, whereas treatment with P2 resulted in reduced protein aggregation, reflecting differences between both <i>G. mellonella</i> PrAMPs antibacterial action. Moreover, both PrAMPs caused a decrease and an increase in the protein content in relation to lipids on the <i>E. coli</i> and <i>M. luteus</i> cell surface, respectively. The obtained results reflect not only differences between the <i>G. mellonella</i> P1 and P2 peptides but also differences in the cell surface between Gram-negative and Gram-positive bacteria. Both characterized <i>G. mellonella</i> PrAMPs are further representatives of proline-rich peptides with a membrane-permeabilizing antimicrobial mode of action.