Membrane Fluidity Modulates Biofilm Formation in E. coli via the Rcs Phosphorelay

Abstract

Lipid membranes are essential for the survival of any cell. The phase behavior of membranes is tightly regulated to maintain their physical integrity and their utility as protein scaffolds. The Escherichia coli inner membrane is composed mainly of three lipid species: phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL). In vitro studies have shown that the presence of CL increases the fluidity of model membranes. Using real-time PCR, we have found that disruption of the three enzymes responsible for CL synthesis—ClsA, ClsB, and ClsC—causes activation of the Rcs signaling pathway. Confocal scanning laser microscopy (CLSM) shows that ΔclsABC biofilms grown under flow are significantly denser than their wild-type counterparts. These mutants also display decreased biofilm formation in crystal violet staining assays. Disruption of the Rcs pathway in a ΔclsABC background restores crystal violet staining to the level of wild-type or better, suggesting that increased Rcs activation is responsible for the observed effects on biofilm formation. We hypothesize the Rcs phosphorelay responds to changes in membrane fluidity, such as that caused by removal of CL from the inner membrane of E. coli.