Modeling Pseudomonas aeruginosa inner plasma membrane in planktonic and biofilm modes

Pseudomonas aeruginosa changes its growth modes under different conditions. The bacteria in biofilm is more resistant to environmental stress compared to the planktonic mode of growth. The compositions of the inner plasma membrane for the two modes are noticeably different. Major lipid types are chosen from experiment to model the membrane in both modes of growth, and molecular dynamics simulation is used to study the properties of the membrane. The CHARMM36 lipid force field is used and tested against several experimental results. Our models include lipids containing cyclopropane in the middle of the sn-2 tail, namely, 1-palmitoyl-2-cis-11,12-methylene-stearic-acid-sn-glycero-3-phosphoethanolamine and 1-palmitoyl-2-cis-11,12-methylene-stearic-acid-sn-glycero-3-phosphoglycerol. The PE:PG ratio for the two model membranes is close, but the fraction of lipids composed of long-chain and cyclopropane-containing fatty acids changes significantly, causing differences between the two models. Compared to previous model membranes built for Escherichia coli, the inner membrane of P. aeruginosa has a longer averaged lipid tail length and a higher percentage of PG lipids, which are responsible for the changes in membrane properties like membrane thickness and stiffness. Most importantly, the comparison to experiments shows good agreements and encourages the model's use to study the behavior of proteins from P. aeruginosa associated with the membrane.