Conjugative type IVb pilus recognizes lipopolysaccharide of recipient cells to initiate PAPI-1 pathogenicity island transfer in Pseudomonas aeruginosa.
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.
Centre for Integrative Biology, University of Trento, 38123, Trento, Italy.
Toan Phuoc
TP
Hong
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA, 02115, USA.
Michelle Q
MQ
Carter
Centre for Integrative Biology, University of Trento, 38123, Trento, Italy.
Paolo
P
Struffi
Centre for Integrative Biology, University of Trento, 38123, Trento, Italy.
Stefano
S
Casonato
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Youai
Y
Hao
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Joseph S
JS
Lam
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA, 02115, USA.
Stephen
S
Lory
Centre for Integrative Biology, University of Trento, 38123, Trento, Italy. olivier.jousson@unitn.it.
Olivier
http://orcid.org/0000-0003-3344-7194
O
Jousson
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D002876:Chromosomes, Bacterial; D003227:Conjugation, Genetic / Q000235:genetics / Q000502:physiology; D010861:Fimbriae, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial / Q000235:genetics / Q000502:physiology; D044404:Genomic Islands / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism*; D005810:Multigene Family; D009154:Mutation; D011552:Pseudomonas Infections / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000472:pathogenicity; D012210:Rhamnose / Q000494:pharmacology; D037521:Virulence Factors / Q000235:genetics
D001426:Bacterial Proteins; D008070:Lipopolysaccharides; D037521:Virulence Factors; D012210:Rhamnose
Horizontal gene transfer; PAPI-1 pathogenicity island; Pseudomonas aeruginosa