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  • Title: Conjugative type IVb pilus recognizes lipopolysaccharide of recipient cells to initiate PAPI-1 pathogenicity island transfer in Pseudomonas aeruginosa.
    Author: Hong TP, Carter MQ, Struffi P, Casonato S, Hao Y, Lam JS, Lory S, Jousson O.
    Journal: BMC Microbiol; 2017 Feb 07; 17(1):31. PubMed ID: 28173753.
    Abstract:
    BACKGROUND: Pseudomonas aeruginosa pathogenicity island 1 (PAPI-1) is one of the largest genomic islands of this important opportunistic human pathogen. Previous studies have shown that PAPI-1 encodes several putative virulence factors, including a major regulator of biofilm formation and antibiotic-resistance traits. PAPI-1 is horizontally transferable into recipient strains lacking this island via conjugation mediated by the specialized type IV pilus. The PAPI-1 encodes a cluster of ten genes associated with the synthesis and assembly of the type IV pilus. The PAPI-1 acquisition mechanism is currently not well understood. RESULTS: In this study, we performed a series of conjugation experiments and identified determinants of PAPI-1 acquisition by analyzing transfer efficiency between the donor and a series of mutant recipient strains. Our data show that common polysaccharide antigen (CPA) lipopolysaccharide (LPS), a homopolymer of D-rhamnose, is required for initiating PAPI-1 transfer, suggesting that this structure acts as a receptor for conjugative type IV pilus in recipient strains. These results were substantiated by experimental evidence from PAPI-1 transfer assay experiments, in which outer membrane or LPS preparations from well-defined LPS mutants were added to the transfer mix to assess the role of P. aeruginosa LPS in PAPI-1 transfer and in vitro binding experiments between pilin fusion protein GST-pilV2' and immobilized LPS molecules were performed. Our data also showed that P. aeruginosa strains that had already acquired a copy of PAPI-1 were unable to import additional copies of the island, and that such strains produced proportionally lower amounts of CPA LPS compared to the strains lacking PAPI-1. CONCLUSIONS: These results suggest that a PAPI-1 exclusion mechanism exists in P. aeruginosa that might serve to regulate the avoidance of uncontrolled expansions of the bacterial genome.
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