Polyunsaturated lipids promote membrane phase separation and antimicrobial sensitivity.

Gram-negative bacteria such as Acinetobacter baumannii sequester host lipids from the site of infection for incorporation into lipid synthesis pathways, altering the membrane lipidome. Changes in membrane composition from the incorporation of host-derived polyunsaturated fatty acids (PUFAs) help restore sensitivity to antimicrobials in several species of Gram-negative bacteria. Using coarse-grained simulations based on lipidomic data of A. baumannii inner membrane collected under three different growth conditions, we show PUFA-incorporation alters membrane biophysical properties, increasing the phase separation between ordered and disordered lipid domains resulting in thinner, less ordered membranes. We show that the changes in A. baumannii membrane biophysical properties on the incorporation of PUFA-containing lipids alter the conformational cycling of RND multidrug efflux pumps and restore sensitivity to some antimicrobials. Finally, we examine the interaction of antimicrobial peptides (AMP) with the simulated A. baumannii membranes to identify the effect of lipid saturation and alterations in membrane properties has on AMP-induced membrane disruption.