title: The Photobacterium damselae subsp. damselae hemolysins damselysin and HlyA are encoded within a new virulence plasmid.
abstract: Photobacterium damselae subsp. damselae (formerly Vibrio damsela) is a marine bacterium that causes infections and fatal disease in a wide range of marine animals and in humans. Highly hemolytic strains produce damselysin (Dly), a cytolysin encoded by the dly gene that is lethal for mice and has hemolytic activity. We found that Dly is encoded in the highly hemolytic strain RM-71 within a 153,429-bp conjugative plasmid that we dubbed pPHDD1. In addition to Dly, pPHDD1 also encodes a homologue of the pore-forming toxin HlyA. We found a direct correlation between presence of pPHDD1 and a strong hemolytic phenotype in a collection of P. damselae subsp. damselae isolates. Hemolysis was strongly reduced in a double dly hlyA mutant, demonstrating the role of the two pPHDD1-encoded genes in hemolysis. Interestingly, although single hlyA and dly mutants showed different levels of hemolysis reduction depending on the erythrocyte source, hemolysis was not abolished in any of the single mutants, suggesting that the hemolytic phenotype is the result of the additive effect of Dly and HlyA. We found that pPHDD1-encoded dly and hlyA genes are necessary for full virulence for mice and fish. Our results suggest that pPHDD1 can be considered as a driving force for the emergence of a highly hemolytic lineage of P. damselae subsp. damselae.
authors.affiliation: Departamento de Microbioloxía e Parasitoloxía, Instituto de Acuicultura, Universidade de Santiago de Compostela, Santiago de Compostela 15782, Galicia, Spain.
authors.forename: Amable J
authors.initials: AJ
authors.lastname: Rivas
authors.forename: Miguel
authors.initials: M
authors.lastname: Balado
authors.forename: Manuel L
authors.initials: ML
authors.lastname: Lemos
authors.forename: Carlos R
authors.initials: CR
authors.lastname: Osorio
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005393:Fish Diseases / Q000382:microbiology; D005412:Flatfishes; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006460:Hemolysin Proteins / Q000235:genetics / Q000378:metabolism*; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D010776:Photobacterium / Q000378:metabolism* / Q000472:pathogenicity*; D010957:Plasmids / Q000378:metabolism*; D012756:Sheep / Q000097:blood; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D006460:Hemolysin Proteins