A (2)H solid-state NMR study of the effect of antimicrobial agents on intact Escherichia coli without mutating.

Solid-state nuclear magnetic resonance (NMR) is a useful tool to probe the organization and dynamics of phospholipids in bilayers. The interactions of molecules with membranes are usually studied with model systems; however, the complex composition of biological membranes motivates such investigations on intact cells. We have thus developed a protocol to deuterate membrane phospholipids in Escherichia coli without mutating to facilitate (2)H solid-state NMR studies on intact bacteria. By exploiting the natural lipid biosynthesis pathway and using perdeuterated palmitic acid, our results show that 76% deuteration of the phospholipid fatty acid chains was attained. To verify the responsiveness of these membrane-deuterated E. coli, the effect of known antimicrobial agents was studied. (2)H solid-state NMR spectra combined to spectral moment analysis support the insertion of the antibiotic polymyxin B lipid tail in the bacterial membrane. The use of membrane-deuterated bacteria was shown to be important in cases where antibiotic action of molecules relies on the interaction with lipopolysaccharides. This is the case of fullerenol nanoparticles which showed a different effect on intact cells when compared to dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol membranes. Our results also suggest that membrane rigidification could play a role in the biocide activity of the detergent cetyltrimethyammonium chloride. Finally, the deuterated E. coli were used to verify the potential antibacterial effect of a marennine-like pigment produced by marine microalgae. We were able to detect a different perturbation of the bacteria membranes by intra- and extracellular forms of the pigment, thus providing valuable information on their action mechanism and suggesting structural differences.