Quorum signal molecules as biosurfactants affecting swarming in Rhizobium etli.
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.
Daniels
Ruth
R
Department of Microbial and Molecular Systems, Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
Reynaert
Sven
S
Hoekstra
Hans
H
Verreth
Christel
C
Janssens
Joost
J
Braeken
Kristien
K
Fauvart
Maarten
M
Beullens
Serge
S
Heusdens
Christophe
C
Lambrichts
Ivo
I
De Vos
Dirk E
DE
Vanderleyden
Jos
J
Vermant
Jan
J
Michiels
Jan
J
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
D001426:Bacterial Proteins; D013501:Surface-Active Agents; C088386:homoserine lactone; D015107:4-Butyrolactone