title: A Natural ChimericPseudomonasBacteriocin with Novel Pore-Forming Activity Parasitizes the Ferrichrome Transporter.
abstract: Modular bacteriocins represent a major group of secreted protein toxins with a narrow spectrum of activity, involved in interference competition between Gram-negative bacteria. These antibacterial proteins include a domain for binding to the target cell and a toxin module at the carboxy terminus. Self-inhibition of producers is provided by coexpression of linked immunity genes that transiently inhibit the toxin's activity through formation of bacteriocin-immunity complexes or by insertion in the inner membrane, depending on the type of toxin module. We demonstrate strain-specific inhibitory activity for PmnH, aPseudomonasbacteriocin with an unprecedented dual-toxin architecture, hosting both a colicin M domain, potentially interfering with peptidoglycan synthesis, and a novel colicin N-type domain, a pore-forming module distinct from the colicin Ia-type domain inPseudomonas aeruginosapyocin S5. A downstream-linked gene product confers PmnH immunity upon susceptible strains. This protein, ImnH, has a transmembrane topology similar to that ofPseudomonascolicin M-like and pore-forming immunity proteins, although homology with either of these is essentially absent. The enhanced killing activity of PmnH under iron-limited growth conditions reflects parasitism of the ferrichrome-type transporter for entry into target cells, a strategy shown here to be used as well by monodomain colicin M-like bacteriocins from pseudomonads. The integration of a second type of toxin module in a bacteriocin gene could offer a competitive advantage against bacteria displaying immunity against only one of both toxic activities.IMPORTANCEIn their continuous struggle for ecological space, bacteria face a huge load of contenders, including phylogenetically related strains that compete for the same niche. One important group of secreted antibacterial proteins assisting in eliminating these rivals are modular bacteriocins of Gram-negative bacteria, comprising a domain for docking onto the cell envelope of a target cell, a translocation domain enabling subsequent cellular entry, and a toxin module that kills target cells via enzymatic or pore-forming activity. We here demonstrate the antagonistic function of aPseudomonasbacteriocin with unique architecture that combines a putative enzymatic colicin M-like domain and a novel pore-forming toxin module. For target cell recognition and entry, this bacteriocin hybrid takes advantage of the ferrichrome transporter, also parasitized by enzymaticPseudomonasbacteriocins devoid of the pore-forming module. Bacteriocins with an expanded toxin potential may represent an inventive bacterial strategy to alleviate immunity in target cells.
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium maarten.ghequire@biw.kuleuven.be.|Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Maarten G K
authors.initials: MG
authors.lastname: Ghequire
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.
authors.forename: Lieselore
authors.initials: L
authors.lastname: Kemland
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Anoz-Carbonell
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Susan K
authors.initials: SK
authors.lastname: Buchanan
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.
authors.forename: René
authors.initials: R
authors.lastname: De Mot
mesh_terms: D001430:Bacteriocins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane; D003087:Colicins / Q000235:genetics; D005291:Ferrichrome / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism*
chemical_list: D001430:Bacteriocins; D003087:Colicins; D026901:Membrane Transport Proteins; D005291:Ferrichrome