Project description:AIP56 (apoptosis-inducing protein of 56 kDa) is a metalloprotease AB toxin secreted by Photobacterium damselae subsp. piscicida that acts by cleaving NF-?B. During infection, AIP56 spreads systemically and depletes phagocytes by postapoptotic secondary necrosis, impairing the host phagocytic defense and contributing to the genesis of infection-associated necrotic lesions. Here we show that mouse bone marrow-derived macrophages (mBMDM) intoxicated by AIP56 undergo NF-?B p65 depletion and apoptosis. Similarly to what was reported for sea bass phagocytes, intoxication of mBMDM involves interaction of AIP56 C-terminal region with cell surface components, suggesting the existence of a conserved receptor. Biochemical approaches and confocal microscopy revealed that AIP56 undergoes clathrin-dependent endocytosis, reaches early endosomes, and follows the recycling pathway. Translocation of AIP56 into the cytosol requires endosome acidification, and an acidic pulse triggers translocation of cell surface-bound AIP56 into the cytosol. Accordingly, at acidic pH, AIP56 becomes more hydrophobic, interacting with artificial lipid bilayer membranes. Altogether, these data indicate that AIP56 is a short-trip toxin that reaches the cytosol using an acidic-pH-dependent mechanism, probably from early endosomes. Usually, for short-trip AB toxins, a minor pool reaches the cytosol by translocating from endosomes, whereas the rest is routed to lysosomes for degradation. Here we demonstrate that part of endocytosed AIP56 is recycled back and released extracellularly through a mechanism requiring phosphoinositide 3-kinase (PI3K) activity but independent of endosome acidification. So far, we have been unable to detect biological activity of recycled AIP56, thereby bringing into question its biological relevance as well as the importance of the recycling pathway.
Project description:AIP56 (apoptosis-inducing protein of 56 kDa) is a key virulence factor of Photobacterium damselae subsp. piscicida (Phdp), the causative agent of a septicaemia affecting warm water marine fish species. Phdp-associated pathology is triggered by AIP56, a short trip AB toxin with a metalloprotease A domain that cleaves the p65 subunit of NF-?B, an evolutionarily conserved transcription factor that regulates the expression of inflammatory and anti-apoptotic genes and plays a central role in host responses to infection. During infection by Phdp, AIP56 is systemically disseminated and induces apoptosis of macrophages and neutrophils, compromising the host phagocytic defence and contributing to the genesis of pathology. Although it is well established that the secretion of AIP56 is crucial for Phdp pathogenicity, the protein secretion systems operating in Phdp and the mechanism responsible for the extracellular release of the toxin remain unknown. Here, we report that Phdp encodes a type II secretion system (T2SS) and show that mutation of the EpsL component of this system impairs AIP56 secretion. This work demonstrates that Phdp has a functional T2SS that mediates secretion of its key virulence factor AIP56.
Project description:The fish pathogen Photobacterium damselae subsp. piscicida produces the siderophore piscibactin. A gene cluster that resembles the Yersinia high-pathogenicity island (HPI) encodes piscibactin biosynthesis. Here, we report that this HPI-like cluster is part of a hitherto-uncharacterized 68-kb plasmid dubbed pPHDP70. This plasmid lacks homologs of genes that mediate conjugation, but we found that it could be transferred at low frequencies from P. damselae subsp. piscicida to a mollusk pathogenic Vibrio alginolyticus strain and to other Gram-negative bacteria, likely dependent on the conjugative functions of the coresident plasmid pPHDP60. Following its conjugative transfer, pPHDP70 restored the capacity of a vibrioferrin mutant of V. alginolyticus to grow under low-iron conditions, and piscibactin became detectable in its supernatant. Thus, pPHDP70 appears to harbor all the genes required for piscibactin biosynthesis and transport. P. damselae subsp. piscicida strains cured of pPHDP70 no longer produced piscibactin, had impaired growth under iron-limited conditions, and exhibited markedly decreased virulence in fish. Collectively, our findings highlight the importance of pPHDP70, with its capacity for piscibactin-mediated iron acquisition, in the virulence of P. damselae subsp. piscicida. Horizontal transmission of this plasmid-borne piscibactin synthesis gene cluster in the marine environment may facilitate the emergence of new pathogens.
Project description:AIP56 (apoptosis inducing protein of 56 kDa) is a key virulence factor secreted by virulent strains of Photobacterium damselae subsp. piscicida (Phdp), a Gram-negative bacterium that causes septicemic infections in several warm water marine fish species. AIP56 is systemically disseminated during infection and induces massive apoptosis of host macrophages and neutrophils, playing a decisive role in the disease outcome. AIP56 is a single-chain AB-type toxin, being composed by a metalloprotease A domain located at the N-terminal region connected to a C-terminal B domain, required for internalization of the toxin into susceptible cells. After binding to a still unidentified surface receptor, AIP56 is internalised through clathrin-mediated endocytosis, reaches early endosomes and translocates into the cytosol through a mechanism requiring endosomal acidification and involving low pH-induced unfolding of the toxin. At the cytosol, the catalytic domain of AIP56 cleaves NF-κB p65, leading to the apoptotic death of the intoxicated cells. It has been reported that host cytosolic factors, including host cell chaperones such as heat shock protein 90 (Hsp90) and peptidyl-prolyl cis/trans isomerases (PPIases), namely cyclophilin A/D (Cyp) and FK506-binding proteins (FKBP) are involved in the uptake of several bacterial AB toxins with ADP-ribosylating activity, but are dispensable for the uptake of other AB toxins with different enzymatic activities, such as Bacillus anthracis lethal toxin (a metalloprotease) or the large glycosylating toxins A and B of Clostridium difficile. Based on these findings, it has been proposed that the requirement for Hsp90/PPIases is a common and specific characteristic of ADP-ribosylating toxins. In the present work, we demonstrate that Hsp90 and the PPIases cyclophilin A/D are required for efficient intoxication by the metalloprotease toxin AIP56. We further show that those host cell factors interact with AIP56 in vitro and that the interactions increase when AIP56 is unfolded. The interaction with Hsp90 was also demonstrated in intact cells, at 30 min post-treatment with AIP56, suggesting that it occurs during or shortly after translocation of the toxin from endosomes into the cytosol. Based on these findings, we propose that the participation of Hsp90 and Cyp in bacterial toxin entry may be more disseminated than initially expected, and may include toxins with different catalytic activities.
Project description:Pseudotuberculosis caused by infection of Photobacterium damselae subsp. piscicida has caused serious economic damages to aquaculture farms worldwide. Here, the whole-genome sequence of P. damselae subsp. piscicida strain OT-51443, isolated in Japan, was determined and suggests that this genome consists of two chromosomes and five plasmids.
Project description:On intensive fish farms, 10% of the population dies exclusively from pathogens, and Photobacterium damselae subsp. Piscicida (Ph. damselae subsp. Piscicida), the bacteria causing pasteurellosis in marine aquaculture, is one of the major pathogens involved. The objective of this study was to obtain new probiotic strains against pasteurellosis in order to limit the use of chemotherapy, avoiding the environmental repercussions generated by the abusive use of these products. In this study, 122 strains were isolated from the gills and intestines of different marine fish species and were later evaluated in vitro to demonstrate the production of antagonistic effects, the production of antibacterial substances, adhesion and growth to mucus, resistance to bile and resistance to pH gradients, as well as its harmlessness and the dynamic of expression of immune-related genes by real-time PCR after administration of the potential probiotic in the fish diet. Only 1/122 strains showed excellent results to be considered as a potential probiotic strain and continue its characterization against Ph. damselae subsp. piscicida to determine its protective effect and elucidating in future studies its use as a possible probiotic strain for marine aquaculture.
Project description:Photobacterium damselae subsp. damselae, an important pathogen of marine animals, may also cause septicemia or hyperaggressive necrotizing fasciitis in humans. We previously showed that hemolysin genes are critical for virulence of this organism in mice and fish. In the present study, we characterized the hlyA gene product, a putative small ?-pore-forming toxin, and termed it phobalysin P (PhlyP), for "photobacterial lysin encoded on a plasmid." PhlyP formed stable oligomers and small membrane pores, causing efflux of K(+), with no significant leakage of lactate dehydrogenase but entry of vital dyes. The latter feature distinguished PhlyP from the related Vibrio cholerae cytolysin. Attack by PhlyP provoked a loss of cellular ATP, attenuated translation, and caused profound morphological changes in epithelial cells. In coculture experiments with epithelial cells, Photobacterium damselae subsp. damselae led to rapid hemolysin-dependent membrane permeabilization. Unexpectedly, hemolysins also promoted the association of P. damselae subsp. damselae with epithelial cells. The collective observations of this study suggest that membrane-damaging toxins commonly enhance bacterial adherence.