title: Contact-dependent growth inhibition requires the essential outer membrane protein BamA (YaeT) as the receptor and the inner membrane transport protein AcrB.
abstract: Contact-dependent growth inhibition (CDI) is a phenomenon by which bacterial cell growth is regulated by direct cell-to-cell contact via the CdiA/CdiB two-partner secretion system. Characterization of mutants resistant to CDI allowed us to identify BamA (YaeT) as the outer membrane receptor for CDI and AcrB as a potential downstream target. Notably, both BamA and AcrB are part of distinct multi-component machines. The Bam machine assembles outer membrane beta-barrel proteins into the outer membrane and the Acr machine exports small molecules into the extracellular milieu. We discovered that a mutation that reduces expression of BamA decreased binding of CDI+ inhibitor cells, measured by flow cytometry with fluorescently labelled bacteria. In addition, alpha-BamA antibodies, which recognized extracellular epitopes of BamA based on immunofluorescence, specifically blocked inhibitor-target cells binding and CDI. A second class of CDI-resistant mutants identified carried null mutations in the acrB gene. AcrB is an inner membrane component of a multidrug efflux pump that normally forms a cell envelope-spanning complex with the membrane fusion protein AcrA and the outer membrane protein TolC. Strikingly, the requirement for the BamA and AcrB proteins in CDI is independent of their multi-component machines, and thus their role in the CDI pathway may reflect novel, import-related functions.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA.
authors.forename: Stephanie K
authors.initials: SK
authors.lastname: Aoki
authors.forename: Juliana C
authors.initials: JC
authors.lastname: Malinverni
authors.forename: Kyle
authors.initials: K
authors.lastname: Jacoby
authors.forename: Benjamin
authors.initials: B
authors.lastname: Thomas
authors.forename: Rupinderjit
authors.initials: R
authors.lastname: Pamma
authors.forename: Brooke N
authors.initials: BN
authors.lastname: Trinh
authors.forename: Susan
authors.initials: S
authors.lastname: Remers
authors.forename: Julia
authors.initials: J
authors.lastname: Webb
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Braaten
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Silhavy
authors.forename: David A
authors.initials: DA
authors.lastname: Low