title: An ABC transporter is required for secretion of peptide sex pheromones in Enterococcus faecalis.
abstract: Enterococci are leading causes of hospital-acquired infection in the United States and continue to develop resistances to new antibiotics. Many Enterococcus faecalis isolates harbor pheromone-responsive plasmids that mediate horizontal transfer of even large blocks of chromosomal genes, resulting in hospital-adapted strains over a quarter of whose genomes consist of mobile elements. Pheromones to which the donor cells respond derive from lipoprotein signal peptides. Using a novel bacterial killing assay dependent on the presence of sex pheromones, we screened a transposon mutant library for functions that relate to the production and/or activity of the effector pheromone. Here we describe a previously uncharacterized, but well-conserved, ABC transporter that contributes to pheromone production. Using three distinct pheromone-dependent mating systems, we show that mutants defective in expressing this transporter display a 5- to 6-order-of-magnitude reduction in conjugation efficiency. In addition, we demonstrate that the ABC transporter mutant displays an altered biofilm architecture, with a significant reduction in biofilm biomass compared to that of its isogenic parent, suggesting that pheromone activity also influences biofilm development. The conservation of this peptide transporter across the Firmicutes suggests that it may also play an important role in cell-cell communication in other species within this important phylum.
  
  
  OBJECTIVE
  Enterococcus faecalis ranks as one of the leading causes of hospital-associated infections. Strains possessing resistance to multiple antibiotics are becoming all too common in clinical settings. Pheromone-responsive plasmids play an important role in harboring and disseminating these antibiotic resistance genes. Here we have identified a novel ABC transporter that is responsible for the secretion of peptide pheromones, which enables communication between cells to mediate plasmid transfer. We have also shown that this transporter is important for biofilm formation, providing a strong rationale for its use as a viable therapeutic target which could be targeted to curb infection, as well as the spread of existing drug resistance.
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA.
authors.forename: Sriram
authors.initials: S
authors.lastname: Varahan
authors.affiliation: Division of Biology, Kansas State University, Manhattan, Kansas, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Harms
authors.affiliation: Departments of Ophthalmology and Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Gilmore
authors.affiliation: Department of Biochemistry, Kansas State University, Manhattan, Kansas, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Tomich
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA lynnh@ku.edu.
authors.forename: Lynn E
authors.initials: LE
authors.lastname: Hancock
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development; D002874:Chromosome Mapping; D004251:DNA Transposable Elements / Q000235:genetics; D024881:Drug Resistance, Bacterial; D013293:Enterococcus faecalis / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D017353:Gene Deletion; D010455:Peptides / Q000378:metabolism*; D010675:Pheromones / Q000378:metabolism*; D010957:Plasmids
chemical_list: D018528:ATP-Binding Cassette Transporters; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D010455:Peptides; D010675:Pheromones