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Mol Microbiol. 2015 Oct;98(1):175-92. doi: 10.1111/mmi.13114. Epub 2015 Jul 30.

CdiA promotes receptor-independent intercellular adhesion.

Author information

1
Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA, 93106-9625, USA.
2
Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, 95064, USA.
3
Centre for Immunology and Infection, Hull York Medical School and the Department of Biology, University of York, York, YO10 5DD, UK.
4
Biomolecular Science and Engineering Program, University of California, Santa Barbara, CA, 93106-9625, USA.

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.

PMID:
26135212
PMCID:
PMC4694591
DOI:
10.1111/mmi.13114
[Indexed for MEDLINE]
Free PMC Article

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