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.

Phobalysin, a Small β-Pore-Forming Toxin of Photobacterium damselae subsp. damselae

“…Previously, we noted that highly hemolytic strains of P. damselae subsp. damselae are particularly virulent (9). Further, the data suggested that hlyA pl plays major roles in both virulence and hemolytic activity (14).…”

“…The bacterial strains and plasmids used in this study are listed in Table 1. Culture conditions and conjugative matings used in this study have been described previously (9,14,15). The Staphylococcus aureus strains have been described previously (24).…”

“…Dly is a phospholipase D that until recently was the only known hemolysin of P. damselae subsp. damselae (10)(11)(12), whereas HlyA pl is a putative pore-forming toxin (PFT) (9). A third, chromosomally encoded hemolysin, HlyA ch , present in all hemolytic strains, is 92% identical to HlyA pl (13), and it makes a minor contribution to hemolysis and virulence (14).…”

“…The virulence of P. damselae subsp. damselae toward mice and fish depends on a large plasmid termed pPHDD1 (9). This conjugative element comprises dly and hlyA pl , which encode two hemolysins: damselysin (Dly) and HlyA pl .…”

Caligus Elongatus and Photobacterium Damselae Subsp Piscicida Concomitant Infections Affecting Broodstock European Seabass, Dicentrarchus Labrax, with Special Reference to Histopathological Responses

“…These ECP were found to be lethal for different fish species including gilthead sea bream and sea bass. Phospholipases, cytotoxic, and hemolytic activities are among the (ECP) produced by this detrimental fish pathogen [9,[57][58][59].…”