Acute hepatopancreatic necrosis disease (AHPND) is a severe, newly emergent penaeid shrimp disease caused by Vibrio parahaemolyticus that has already led to tremendous losses in the cultured shrimp industry. Until now, its disease-causing mechanism has remained unclear. Here we show that an AHPND-causing strain of V. parahaemolyticus contains a 70-kbp plasmid (pVA1) with a postsegregational killing system, and that the ability to cause disease is abolished by the natural absence or experimental deletion of the plasmid-encoded homologs of the Photorhabdus insect-related (Pir) toxins PirA and PirB. We determined the crystal structure of the V. parahaemolyticus PirA and PirB (PirAvp and PirBvp) proteins and found that the overall structural topology of PirAvp/PirBvp is very similar to that of the Bacillus Cry insecticidal toxin-like proteins, despite the low sequence identity (<10%). This structural similarity suggests that the putative PirABvp heterodimer might emulate the functional domains of the Cry protein, and in particular its pore-forming activity. The gene organization of pVA1 further suggested that pirABvp may be lost or acquired by horizontal gene transfer via transposition or homologous recombination.

The halophile Vibrio vulnificus is an etiologic agent of human mortality from seafood-borne infections. We applied whole-genome sequencing and comparative analysis to investigate the evolution of this pathogen. The genome of biotype 1 strain, V. vulnificus YJ016, was sequenced and includes two chromosomes of estimated 3377 kbp and 1857 kbp in size, and a plasmid of 48,508 bp. A super-integron (SI) was identified, and the SI region spans 139 kbp and contains 188 gene cassettes. In contrast to non-SI sequences, the captured gene cassettes are unique for any given Vibrio species and are highly variable among V. vulnificus strains. Multiple rearrangements were found when comparing the 5.3-Mbp V. vulnificus YJ016 genome and the 4.0-Mbp V. cholerae El Tor N16961 genome. The organization of gene clusters of capsular polysaccharide, iron metabolism, and RTX toxin showed distinct genetic features of V. vulnificus and V. cholerae. The content of the V. vulnificus genome contained gene duplications and evidence of horizontal transfer, allowing for genetic diversity and function in the marine environment. The genomic information obtained in this study can be applied to monitoring vibrio infections and identifying virulence genes in V. vulnificus.[Supplemental material is available online at www.genome.org and at http://genome.nhri.org.tw/vv/. The nucleotide sequence data from this study have been submitted to DDBJ/EMBL/GenBank under accession nos. BA000037, BA000038, and AP005352.]Vibrio vulnificus is an etiologic agent for severe human infection acquired through wounds or contaminated seafood. This organism is divided into three biotypes according to their different biochemical and biological properties (Linkous and Oliver 1999). Among them the biotype 1 strains are most frequently isolated from the clinical specimens. Opportunistic infection in susceptible individuals typically causes mortality within 24 to 48 h of the exposure. The bacterium is halophilic, and it is abundantly present in estuarine ecosystems throughout the world. Isolated incidents of V. vulnificus infection have been reported in the U.S.A., Europe, Korea, Taiwan (Park et al. 1991;Chuang et al. 1992;Dalsgaard et al. 1996;Hlady and Klontz 1996), and many other countries. According to CDC statistics, V. vulnificus is a major bacterial cause of mortality associated with food-borne diseases, and it results in the highest death rate of any causative agent (Todd 1989).V. vulnificus belongs to the ␥-group of Proteobacteria, and it shares morphological and biochemical characteristics with other human vibrio pathogens, including Vibrio cholerae and Vibrio parahaemolyticus. Bacteria of the Vibrionaceae family, which show a comma-shape microscopic appearance and a polar flagellum appendage, are mostly aquatic inhabitants that require NaCl for optimal growth. On the basis of clinical and epidemiology studies, diseases associated with V. vulnificus infection have been found to present in two patterns (Blake et al. 1979). In one, primary septicemia occurred in individ...

Vibrio vulnificus is a marine bacterium causing serious septicemia and wound infection in humans. It produces an RTX toxin that can lyse a variety of cells and is important for virulence in mice. In this study, we explored the role of RTX in pathogenesis by characterizing an RTX-deficient mutant. This mutant showed an ∼2-log reduction in virulence for mice infected by various routes. Survival of the mutant at the infection site and subsequent spread into the bloodstream were impaired. In mice pretreated with cyclophosphamide to deplete the neutrophils, both the virulence and survival at the infection site of this mutant were enhanced. This mutant was further shown to be more readily cleared from the macrophage-rich mouse peritoneal cavity and phagocytosed by murine macrophages. These findings suggest that the RTX of V. vulnificus is required for bacterial survival during infection by protecting the organism from phagocytosis.

Previous work suggested that a metalloprotease, Vvp, may be a virulence factor of Vibrio vulnificus, which causes severe wound infection and septicemia in humans. To determine the role of Vvp in pathogenesis, we isolated an isogenic protease-deficient (PD) mutant of Vibrio vulnificus by in vivo allelic exchange. This PD mutant was as virulent as its parental strain in mice infected intraperitoneally and was 10-fold more virulent in mice infected via the oral route. Furthermore, the PD mutant was indistinguishable from its parental strain in invasion from peritoneal cavity into blood stream, enhancement of vascular permeability, growth in murine blood, and utilization of hemoglobin and transferrin. These data suggest that Vvp is not essential for virulence in the mouse. However, the cytolysin activity in the culture supernatant of the PD mutant was found to be twofold higher than that of the wild-type strain and remained for a much longer period. The higher cytolysin activity of the PD mutant may be associated with the enhanced virulence in mice infected via the oral route.Vibrio vulnificus, a halophilic gram-negative marine bacterium, causes infectious diseases in humans, especially in people who are immunocompromised or have underlying conditions such as hemochromatosis, liver cirrhosis, or alcoholism (3,4,5,29). It mainly produces two types of disease: primary sepsis via gastrointestinal infection, and wound infection. In either case, skin lesions with ulcer and edema are observed (13,15,36,37).This organism produces a few extracellular products implicated in bacterial virulence and pathogenesis, including cytolysin, protease, phospholipases, and siderophores (17,18,24,38). Only a single extracellular protease (designated Vvp) has been identified (16,24). This protease has been shown to increase vascular permeability and edema through activating the Hageman factor-plasma kallikrein-kinin cascade (25,26,27). It can also facilitate iron acquisition by the organism by digesting heme proteins, transferrin, and lactoferrin (31). Recently, Miyoshi et al. reported that the purified protease is able to cause hypodermic hemorrhage in guinea pigs (28). Based on these observations, Vvp was thought to be important in bacterial growth and disease developments.We have previously cloned the vvp gene (6), which encodes a protease with its amino acid composition and the N-terminal sequence derived from the deduced amino acid sequence identical to those of the purified Vvp (16). To further determine the role of Vvp in pathogenesis by genetic approaches, we isolated a protease-deficient (PD) mutant by introducing an in-frame deletion to the vvp gene of a clinical V. vulnificus strain using an allelic exchange technique. By comparing the pathogenicity of this PD mutant with that of its parental strain, we would be able to determine whether the protease is an important virulence factor. Here we report the characterization of this PD mutant with respect to (i) virulence in mice, (ii) ability to invade the blood stream from the peri...