Effects Of Membrane Lipid Composition And Substructures On Biomechanical Properties Of E.coli

The biomechanical properties（e.g.rigidity and adhesion）play vital roles in the physiological and pathological processes（e.g.bacterial adhesion and infection）.Presently,the effects of various drugs on bacterial rigidity and adhesion have been extensively studied.However,the effects of bacterial substructures on bacterial rigidity and the effects of lipid constituents of bacteria on bacterial adhesion are less investigated.In this study,the effects of bacterial substructures on bacterial rigidity were first evaluated.Four types of Escherichia coli（E.coli）with different lipid constituents,including DH5a(P^E+PC^-),AD93/pDD72（PE⁺PC^-）,AD93/ptac67（PE^-PC⁺）,AD93（PE^-PC^-）were utilized to study the effects of lipid constituents on bacterial rigidity;in order to investigate the effects of various bacterial substructures on bacterial rigidity,three antimicrobial drugs including EDTA,lysozyme,and streptomycin,were used to change the integrated outer membrane,cell wall,and bacterial content.We found that different substructures of E.coli contributed to the rigidity of E.coli to different extents and that the peptidoglycan layer（cell wall）and the cytoplasmic contents were the major determinants whereas membrane lipid composition is the minor one.Our data may provide useful information for understanding the properties and behaviors of bacteria.Next,the effects of lipid constituents on bacterial adhesion were studied.Five types of substrates with different hydrophobic/hydrophilic properties（including normal glass,hydrophilic-glass,OTS-glass,plastic,and ceramic）and one type of cell line（macrophage）were applied to study the adhesive properties of the four types of E.coli.The hydrophobic/hydrophilic property of a substrate significantly influenced bacterial adhesion consistent with previous reports.Interestingly,however,when phosphatidylethanolamine（PE）was deficient,the adhesive ability of E.coli（the PE-PC-and PE-PC+strains）onto substrates or cells decreased dramatically which could not be affected by the hydrophilic/hydrophobic properties of substrates and the replenishment of phosphatidylcholin（PC）,implying that the lipid composition（mainly PE）is the major determinant of bacterial adhesion.Further study found that the content of lipopolysaccharide（LPS）on PE-E.coli strains decreased dramatically,implying that the change in lipid composition（e.g.PE）of bacteria may influence bacterial adhesion via altering the content of LPS.The data may provide us an idea for inhibiting bacterial adhesion/infection by regulating PE content of bacterial outer membrane.