title: Quorum signal molecules as biosurfactants affecting swarming in Rhizobium etli.
abstract: Swarming motility is suggested to be a social phenomenon that enables groups of bacteria to coordinately and rapidly move atop solid surfaces. This multicellular behavior, during which the apparently organized bacterial populations are embedded in an extracellular slime layer, has previously been linked with biofilm formation and virulence. Many population density-controlled activities involve the activation of complex signaling pathways using small diffusible molecules, also known as autoinducers. In Gram-negative bacteria, quorum sensing (QS) is achieved primarily by means of N-acylhomoserine lactones (AHLs). Here, we report on a dual function of AHL molecules in controlling swarming behavior of Rhizobium etli, the bacterial symbiotic partner of the common bean plant. The major swarming regulator of R. etli is the cinIR QS system, which is specifically activated in swarming cells by its cognate AHL and other long-chain AHLs. This signaling role of long-chain AHLs is required for high-level expression of the cin and rai QS systems. Besides this signaling function, the long-chain AHLs also have a direct role in surface movement of swarmer cells as these molecules possess significant surface activity and induce liquid flows, known as Marangoni flows, as a result of gradients in surface tension at biologically relevant concentrations. These results point to an as-yet-undisclosed direct role of long-chain AHL molecules as biosurfactants.
authors.affiliation: Department of Microbial and Molecular Systems, Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
authors.forename: Ruth
authors.initials: R
authors.lastname: Daniels
authors.forename: Sven
authors.initials: S
authors.lastname: Reynaert
authors.forename: Hans
authors.initials: H
authors.lastname: Hoekstra
authors.forename: Christel
authors.initials: C
authors.lastname: Verreth
authors.forename: Joost
authors.initials: J
authors.lastname: Janssens
authors.forename: Kristien
authors.initials: K
authors.lastname: Braeken
authors.forename: Maarten
authors.initials: M
authors.lastname: Fauvart
authors.forename: Serge
authors.initials: S
authors.lastname: Beullens
authors.forename: Christophe
authors.initials: C
authors.lastname: Heusdens
authors.forename: Ivo
authors.initials: I
authors.lastname: Lambrichts
authors.forename: Dirk E
authors.initials: DE
authors.lastname: De Vos
authors.forename: Jos
authors.initials: J
authors.lastname: Vanderleyden
authors.forename: Jan
authors.initials: J
authors.lastname: Vermant
authors.forename: Jan
authors.initials: J
authors.lastname: Michiels
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D005798:Genes, Bacterial / Q000235:genetics; D057927:Hydrophobic and Hydrophilic Interactions; D009068:Movement; D009154:Mutation / Q000235:genetics; D010933:Plankton / Q000378:metabolism; D042163:Rhizobium etli / Q000166:cytology / Q000502:physiology*; D033081:Shear Strength; D015398:Signal Transduction; D013500:Surface Tension; D013501:Surface-Active Agents / Q000378:metabolism*; D014783:Viscosity
chemical_list: D001426:Bacterial Proteins; D013501:Surface-Active Agents; C088386:homoserine lactone; D015107:4-Butyrolactone