title: Morphological and nanostructural surface changes in Escherichia coli over time, monitored by atomic force microscopy.
abstract: The present study aims at evaluating intrinsic changes in Escherichia coli (E. coli) surface over time, by Atomic Force Microscopy (AFM). For that purpose, bacteria were immobilized on mica or on mica previously functionalized by the deposition of a polyelectrolyte multilayer cushion. AFM images reveal that E. coli population goes through different stages. Firstly, after a week, the number of healthy bacteria decreases resulting in a release of cellular components which likely become, in turn, a nutrition source for increasing the healthy population after around two weeks. Finally, after one month, most of the bacteria is dead. Our study shows a transition of a healthy rod-shaped bacterium to a dead collapsed one. Most importantly, along with the morphological evolution of bacteria, are the structure changes and the mechanical properties of their outer membrane, emphasized by AFM phase images with very high resolution. Indeed, the surface of healthy bacteria is characterized by a phase separation pattern, thereafter mentioned as "ripples". Bacterial ageing goes along with the loss of this organized structure, turning into circular areas with irregular boundaries. These changes are likely caused by a re-organization, due to external stress, of mainly lipopolysaccharides (LPS) present in the outer membrane of E. coli.
authors.affiliation: Université de Bordeaux, LOMA, CNRS UMR 5798, 351 Cours de la Libération, 33405 Talence, France. Electronic address: ibtissem.gammoudi@u-bordeaux.fr.
authors.forename: Ibtissem
authors.initials: I
authors.lastname: Gammoudi
authors.affiliation: Université de Bordeaux, LOMA, CNRS UMR 5798, 351 Cours de la Libération, 33405 Talence, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Mathelie-Guinlet
authors.affiliation: Université de Bordeaux, LOMA, CNRS UMR 5798, 351 Cours de la Libération, 33405 Talence, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Morote
authors.affiliation: Université de Bordeaux, INRA, CNRS UMR 1332 BFP, 71 Avenue Edouard Bourlaux, 33882 Villenave d'Ornon Cedex, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Beven
authors.affiliation: Université de Bordeaux, INSERM U1035, Bordeaux 33706, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Moynet
authors.affiliation: Université de Bordeaux, LOMA, CNRS UMR 5798, 351 Cours de la Libération, 33405 Talence, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Grauby-Heywang
authors.affiliation: Université de Bordeaux, LOMA, CNRS UMR 5798, 351 Cours de la Libération, 33405 Talence, France. Electronic address: touria.cohen-bouhacina@u-bordeaux.fr.
authors.forename: Touria
authors.initials: T
authors.lastname: Cohen-Bouhacina
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D018441:Biofilms; D002462:Cell Membrane / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure; D008070:Lipopolysaccharides / Q000737:chemistry; D050296:Microbial Viability; D018625:Microscopy, Atomic Force / Q000379:methods*; D049329:Nanostructures / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D008070:Lipopolysaccharides; C011934:mica
keywords: Ageing; Atomic Force Microscopy; Escherichia coli; Gram negative bacteria; Lipopolysaccharide; Membrane