LAUSR

The cell envelope in Gram-negative bacteria is made of two distinct membranes and a cell wall between them. Although there is growing interest in the mechanical adaptation of this cell envelope to turgor pressure, how the cell wall, the inner membrane (IM), and the outer membrane (OM) couple together to provide this adaption remains unexplored. In this study, we have used molecular dynamics (MD) simulations to resolve how lipid membranes and cell wall respond to changes in lateral tension, such as might result from an osmotic gradient. Simulations of individual membranes as well as membranes coupled to the cell wall were also carried out. Our inner membrane model consists of saturated, unsaturated, and cycle-containing lipids while our outer membrane model contains an outer leaflet of lipopolysaccharides; both membranes accurately reflect the diverse population of lipids found in each experimentally. We have measured the mechanical properties of each membrane at protein concentrations ranging from 0 to 50%. In order to describe the membranes’ elasticity, we focused on the low-tension regime (elastic regime), which can be exploited to measure the area compressibility modulus and Young's modulus. The high-tension, non-linear regime was also studied for the cell wall, leading to the observation of stress stiffening.