title: Nanoscale cell wall deformation impacts long-range bacterial adhesion forces on surfaces.
abstract: Adhesion of bacteria occurs on virtually all natural and synthetic surfaces and is crucial for their survival. Once they are adhering, bacteria start growing and form a biofilm, in which they are protected against environmental attacks. Bacterial adhesion to surfaces is mediated by a combination of different short- and long-range forces. Here we present a new atomic force microscopy (AFM)-based method to derive long-range bacterial adhesion forces from the dependence of bacterial adhesion forces on the loading force, as applied during the use of AFM. The long-range adhesion forces of wild-type Staphylococcus aureus parent strains (0.5 and 0.8 nN) amounted to only one-third of these forces measured for their more deformable isogenic Δpbp4 mutants that were deficient in peptidoglycan cross-linking. The measured long-range Lifshitz-Van der Waals adhesion forces matched those calculated from published Hamaker constants, provided that a 40% ellipsoidal deformation of the bacterial cell wall was assumed for the Δpbp4 mutants. Direct imaging of adhering staphylococci using the AFM peak force-quantitative nanomechanical property mapping imaging mode confirmed a height reduction due to deformation in the Δpbp4 mutants of 100 to 200 nm. Across naturally occurring bacterial strains, long-range forces do not vary to the extent observed here for the Δpbp4 mutants. Importantly, however, extrapolating from the results of this study, it can be concluded that long-range bacterial adhesion forces are determined not only by the composition and structure of the bacterial cell surface but also by a hitherto neglected, small deformation of the bacterial cell wall, facilitating an increase in contact area and, therewith, in adhesion force.
authors.affiliation: University of Groningen and University Medical Center Groningen, Department of Biomedical Engineering, Groningen, The Netherlands.
authors.forename: Yun
authors.initials: Y
authors.lastname: Chen
authors.forename: Akshay K
authors.initials: AK
authors.lastname: Harapanahalli
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Busscher
authors.forename: Willem
authors.initials: W
authors.lastname: Norde
authors.forename: Henny C
authors.initials: HC
authors.lastname: van der Mei
mesh_terms: D001422:Bacterial Adhesion; D002473:Cell Wall / Q000648:ultrastructure*; D057446:Hydrodynamics; D018625:Microscopy, Atomic Force / Q000379:methods*; D009154:Mutation; D010457:Peptidoglycan / Q000235:genetics / Q000378:metabolism; D010933:Plankton / Q000382:microbiology; D013211:Staphylococcus aureus / Q000166:cytology* / Q000235:genetics / Q000502:physiology; D013499:Surface Properties
chemical_list: D010457:Peptidoglycan