title: Cooperation and conflict in microbial biofilms.
abstract: Biofilms, in which cells attach to surfaces and secrete slime (polymeric substances), are central to microbial life. Biofilms are often thought to require high levels of cooperation because extracellular polymeric substances are a shared resource produced by one cell that can be used by others. Here we examine this hypothesis by using a detailed individual-based simulation of a biofilm to investigate the outcome of evolutionary competitions between strains that differ in their level of polymer production. Our model includes a biochemical description of the carbon fluxes for growth and polymer production, and it explicitly calculates diffusion-reaction effects and the resulting solute gradients in the biofilm. An emergent property of these simple but realistic mechanistic assumptions is a strong evolutionary advantage to extracellular polymer production. Polymer secretion is altruistic to cells above a focal cell: it pushes later generations in their lineage up and out into better oxygen conditions, but it harms others; polymer production suffocates neighboring nonpolymer producers. This property, analogous to vertical growth in plants, suggests that polymer secretion provides a strong competitive advantage to cell lineages within mixed-genotype biofilms: global cooperation is not required. Our model fundamentally changes how biofilms are expected to respond to changing social conditions; the presence of multiple strains in a biofilm should promote rather than inhibit polymer secretion.
authors.affiliation: Center for Systems Biology, Harvard University, Bauer Laboratory, 7 Divinity Avenue, Cambridge, MA 02138, USA.
authors.forename: Joao B
authors.initials: JB
authors.lastname: Xavier
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Foster
mesh_terms: D018441:Biofilms; D001704:Biopolymers / Q000378:metabolism; D003198:Computer Simulation; D008829:Microbiology; D008954:Models, Biological; D009154:Mutation / Q000235:genetics
chemical_list: D001704:Biopolymers