Title: 2 H NMR Studies of Bacteria: How Does the Peptidoglycan Layer Modify the Interaction between Antimicrobial Peptides and the Lipid Membrane
Abstract: Antimicrobial peptides (AMPs) are a group of small peptides with antimicrobial effects against pathogens and have been well studied because of their promise to be part of the solution to the rising problem of antibiotic resistance. Biophysical studies with AMPs in model lipid systems are commonly used to study AMPs' permeabilizing effect on lipid bilayers. However, it is not clear if this membrane-permeabilizing characteristic is the only mechanism of cell killing. Studies suggest that at least some AMPs have additional targets, different from the lipid bilayer. This studies lead to the suggestion that membrane permeabilization is just part of a multi-hit mechanism of AMPs, or even just a collateral effect. Additionally, AMP interactions with non-lipid cell envelope components of bacteria may be important in modifying how well AMPs are able to disrupt the lipid membrane. In order to connect studies of AMPs in model lipid systems to the more complex real bacterial cell envelopes, we have deuterium-labeled the membranes of the gram-positive bacteria Bacillus subtilis and used 2H NMR to study how lipid acyl chain order in its membranes is affected by treatment with AMPs. We have also observed 2H NMR spectra from Bacillus subtilis in which the peptidoglycan layer has been disrupted. This has allowed us to investigate how disruption of the peptidoglycan layer affects bacterial lipid chain order and the AMP/bacteria interaction.