title: CdiA promotes receptor-independent intercellular adhesion.
abstract: CdiB/CdiA proteins mediate inter-bacterial competition in a process termed contact-dependent growth inhibition (CDI). Filamentous CdiA exoproteins extend from CDI(+) cells and bind specific receptors to deliver toxins into susceptible target bacteria. CDI has also been implicated in auto-aggregation and biofilm formation in several species, but the contribution of CdiA-receptor interactions to these multi-cellular behaviors has not been examined. Using Escherichia coli isolate EC93 as a model, we show that cdiA and bamA receptor mutants are defective in biofilm formation, suggesting a prominent role for CdiA-BamA mediated cell-cell adhesion. However, CdiA also promotes auto-aggregation in a BamA-independent manner, indicating that the exoprotein possesses an additional adhesin activity. Cells must express CdiA in order to participate in BamA-independent aggregates, suggesting that adhesion could be mediated by homotypic CdiA-CdiA interactions. The BamA-dependent and BamA-independent interaction domains map to distinct regions within the CdiA filament. Thus, CdiA orchestrates a collective behavior that is independent of its growth-inhibition activity. This adhesion should enable 'greenbeard' discrimination, in which genetically unrelated individuals cooperate with one another based on a single shared trait. This kind-selective social behavior could provide immediate fitness benefits to bacteria that acquire the systems through horizontal gene transfer.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, 93106-9625, USA.
authors.forename: Zachary C
authors.initials: ZC
authors.lastname: Ruhe
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, 95064, USA.
authors.forename: Loni
authors.initials: L
authors.lastname: Townsley
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, 93106-9625, USA.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Wallace
authors.affiliation: Centre for Immunology and Infection, Hull York Medical School and the Department of Biology, University of York, York, YO10 5DD, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: King
authors.affiliation: Centre for Immunology and Infection, Hull York Medical School and the Department of Biology, University of York, York, YO10 5DD, UK.
authors.forename: Marjan W
authors.initials: MW
authors.lastname: Van der Woude
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, 93106-9625, USA.|Biomolecular Science and Engineering Program, University of California, Santa Barbara, CA, 93106-9625, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Low
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, 95064, USA.
authors.forename: Fitnat H
authors.initials: FH
authors.lastname: Yildiz
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, 93106-9625, USA.|Biomolecular Science and Engineering Program, University of California, Santa Barbara, CA, 93106-9625, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hayes
mesh_terms: D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development*; D003260:Contact Inhibition; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D022761:Gene Transfer, Horizontal; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation
chemical_list: D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; C503242:CdiA protein, E coli; D029968:Escherichia coli Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins