Effect of AMPs MSI-78 and BP100 on the lipid acyl chains of 2H-labeled intact Gram positive bacteria

The lipid bilayer disrupting effect of antimicrobial peptides (AMPs) has been widely studied in model-lipid systems by applying biophysical techniques such as 2H NMR spectroscopy. Real bacteria cell envelopes contain non-lipid components, such as peptidoglycan, and thus it is important to assess the effects of such non-lipid components on the lipid-disrupting effects of AMPs. To this end, our group and other have developed methods that promote uptake of deuterium-labeled acyl chains in bacterial cells to produce 2H-membrane-enriched Bacillus subtilis. In this work, we studied changes in the static 2H NMR spectra of B. subtilis induced by the AMPs MSI-78 and BP100. Addition of both AMPs resulted in the increase of lipid acyl chain disorder consistent with disruption of the bacterial membrane. In addition, the peptide to lipid molar ratios (P:L) that give rise to observable effects fall between the P:L molar ratios necessary to generate membrane disruption in model-lipid-only systems and the P:L molar ratios needed to inhibit bacterial cell growth. This observation supports a role for the non-lipid components in modulating the AMP-lipid interactions.