title: Coordinated cyclic-di-GMP repression of Salmonella motility through YcgR and cellulose.
abstract: Cyclic di-GMP (c-di-GMP) is a secondary messenger that controls a variety of cellular processes, including the switch between a biofilm and a planktonic bacterial lifestyle. This nucleotide binds to cellular effectors in order to exert its regulatory functions. In Salmonella, two proteins, BcsA and YcgR, both of them containing a c-di-GMP binding PilZ domain, are the only known c-di-GMP receptors. BcsA, upon c-di-GMP binding, synthesizes cellulose, the main exopolysaccharide of the biofilm matrix. YcgR is dedicated to c-di-GMP-dependent inhibition of motility through its interaction with flagellar motor proteins. However, previous evidences indicate that in the absence of YcgR, there is still an additional element that mediates motility impairment under high c-di-GMP levels. Here we have uncovered that cellulose per se is the factor that further promotes inhibition of bacterial motility once high c-di-GMP contents drive the activation of a sessile lifestyle. Inactivation of different genes of the bcsABZC operon, mutation of the conserved residues in the RxxxR motif of the BcsA PilZ domain, or degradation of the cellulose produced by BcsA rescued the motility defect of ΔycgR strains in which high c-di-GMP levels were reached through the overexpression of diguanylate cyclases. High c-di-GMP levels provoked cellulose accumulation around cells that impeded flagellar rotation, probably by means of steric hindrance, without affecting flagellum gene expression, exportation, or assembly. Our results highlight the relevance of cellulose in Salmonella lifestyle switching as an architectural element that is both essential for biofilm development and required, in collaboration with YcgR, for complete motility inhibition.
authors.affiliation: Laboratory of Microbial Biofilms, Instituto de Agrobiotecnología, Idab, Universidad Pública de Navarra-CSIC-Gobierno de Navarra, Pamplona, Navarra, Spain.
authors.forename: Violeta
authors.initials: V
authors.lastname: Zorraquino
authors.forename: Begoña
authors.initials: B
authors.lastname: García
authors.forename: Cristina
authors.initials: C
authors.lastname: Latasa
authors.forename: Maite
authors.initials: M
authors.lastname: Echeverz
authors.forename: Alejandro
authors.initials: A
authors.lastname: Toledo-Arana
authors.forename: Jaione
authors.initials: J
authors.lastname: Valle
authors.forename: Iñigo
authors.initials: I
authors.lastname: Lasa
authors.forename: Cristina
authors.initials: C
authors.lastname: Solano
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D005407:Flagella / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D009068:Movement / Q000502:physiology; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D012399:Rotation; D012477:Salmonella enteritidis / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial; C062025:bis(3',5')-cyclic diguanylic acid; D002482:Cellulose; D000429:Alcohol Oxidoreductases; C021496:lactate-malate transhydrogenase; D006152:Cyclic GMP