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...

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