Author:

Abstract:

Pseudomonads are equipped with an arsenal of antagonism-mediating compounds to harness themselves in competitive environments. One well-studied group are secreted antibacterial proteins or bacteriocins, and these molecules are currently under renewed interest for medical applications. Their high selectivity, efficacy and biodegradability make them an attractive drug lead for cocktail development. A major subset of these bacteriocins are synthesized as modular proteins and include a receptor-binding domain, an outer-membrane translocating domain and a toxin-immunity module at the C-terminus. Here we focused on a Pseudomonas bacteriocin with an unprecedented dual toxin architecture, combining a domain likely interfering with peptidoglycan synthesis, with a novel type pore forming domain, distinct form the one previously studied in pseudomonads. We demonstrate that strain-specific inhibitory activity of recombinantly-produced bacteriocin is directed against strains that are phylogenetically related to the producer. Killing activity of this natural bacteriocin hybrid is significantly enhanced under iron-poor growing conditions, suggesting the targeting of an outer-membrane receptor that is upregulated under similar conditions. Via transposon mutagenesis we identified multiple mutants that became resistant to bacteriocin killing and were hit in the same receptor gene. In addition, we could also demonstrate that this receptor is equally used by Pseudomonas bacteriocins that only host the peptidoglycan-interfering module. In close proximity of this bacteriocin gene a candidate immunity factor that adopts a transmembrane topology that is common to the immunity factor of both killing modules, could be identified. The functional characterization of a bacteriocin with a bimodular toxin organization could offer an evolutionary advantage for producer strains and may represent a cunning bacterial tool to alleviate niches from cheaters displaying orphan immunity.