title: Cell-cell contacts confine public goods diffusion inside Pseudomonas aeruginosa clonal microcolonies.
abstract: The maintenance of cooperation in populations where public goods are equally accessible to all but inflict a fitness cost on individual producers is a long-standing puzzle of evolutionary biology. An example of such a scenario is the secretion of siderophores by bacteria into their environment to fetch soluble iron. In a planktonic culture, these molecules diffuse rapidly, such that the same concentration is experienced by all bacteria. However, on solid substrates, bacteria form dense and packed colonies that may alter the diffusion dynamics through cell-cell contact interactions. In Pseudomonas aeruginosa microcolonies growing on solid substrate, we found that the concentration of pyoverdine, a secreted iron chelator, is heterogeneous, with a maximum at the center of the colony. We quantitatively explain the formation of this gradient by local exchange between contacting cells rather than by global diffusion of pyoverdine. In addition, we show that this local trafficking modulates the growth rate of individual cells. Taken together, these data provide a physical basis that explains the stability of public goods production in packed colonies.
authors.affiliation: Laboratoire de Physique Statistique, Ecole Normale Superieure, UPMC Univ Paris 06, Université Paris Diderot, CNRS, 75005 Paris, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Julou
authors.forename: Thierry
authors.initials: T
authors.lastname: Mora
authors.forename: Laurent
authors.initials: L
authors.lastname: Guillon
authors.forename: Vincent
authors.initials: V
authors.lastname: Croquette
authors.forename: Isabelle J
authors.initials: IJ
authors.lastname: Schalk
authors.forename: David
authors.initials: D
authors.lastname: Bensimon
authors.forename: Nicolas
authors.initials: N
authors.lastname: Desprat
mesh_terms: D001692:Biological Transport / Q000502:physiology; D007501:Iron / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000502:physiology*
chemical_list: D009842:Oligopeptides; C042453:pyoverdin; D007501:Iron
keywords: biofilm; ecology; evolution; noise; variability