title: Vertical stratification of matrix production is essential for physical integrity and architecture of macrocolony biofilms of Escherichia coli.
abstract: Bacterial macrocolony biofilms grow into intricate three-dimensional structures that depend on self-produced extracellular polymers conferring protection, cohesion and elasticity to the biofilm. In Escherichia coli, synthesis of this matrix - consisting of amyloid curli fibres and cellulose - requires CsgD, a transcription factor regulated by the stationary phase sigma factor RpoS, and occurs in the nutrient-deprived cells of the upper layer of macrocolonies. Is this asymmetric matrix distribution functionally important or is it just a fortuitous by-product of an unavoidable nutrient gradient? In order to address this question, the RpoS-dependent csgD promoter was replaced by a vegetative promoter. This re-wiring of csgD led to CsgD and matrix production in both strata of macrocolonies, with the lower layer transforming into a rigid 'base plate' of growing yet curli-connected cells. As a result, the two strata broke apart followed by desiccation and exfoliation of the top layer. By contrast, matrix-free cells at the bottom of wild-type macrocolonies maintain colony contact with the humid agar support by flexibly filling the space that opens up under buckling areas of the macrocolony. Precisely regulated stratification in matrix-free and matrix-producing cell layers is thus essential for the physical integrity and architecture of E. coli macrocolony biofilms.
authors.affiliation: Institut für Biologie/Mikrobiologie, Humboldt-Universität zu Berlin, Berlin, 10115, Germany.
authors.forename: Diego O
authors.initials: DO
authors.lastname: Serra
authors.affiliation: Institut für Biologie/Mikrobiologie, Humboldt-Universität zu Berlin, Berlin, 10115, Germany.
authors.forename: Gisela
authors.initials: G
authors.lastname: Klauck
authors.affiliation: Institut für Biologie/Mikrobiologie, Humboldt-Universität zu Berlin, Berlin, 10115, Germany.
authors.forename: Regine
authors.initials: R
authors.lastname: Hengge
mesh_terms: D000682:Amyloid / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics*; D018441:Biofilms / Q000254:growth & development*; D004926:Escherichia coli / Q000235:genetics* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics*; D005109:Extracellular Matrix / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics*
chemical_list: D000682:Amyloid; D001426:Bacterial Proteins; C499694:CsgD protein, E coli; D029968:Escherichia coli Proteins; D012808:Sigma Factor; D015534:Trans-Activators; C069567:sigma factor KatF protein, Bacteria