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A group of phenotypically similar bacteria were isolated during a survey in 1995 to determine the distribution of pathogenic Vibrio vulnificus in sewage of the Baltic sea. These strains could not be assigned to any of the currently known Vibrio species. The present work suggests these strains represent a new Vibrio species, described as Vibrio pommerensis sp. nov. The presented data demonstrate the phenotypic as -vwil as genotypic distance to other Vibrio species. A typical representative strain of Vibrio pommerensis sp. nov., strain CH-291, lysed washed erythrocytes of both humans and animals. Hemolysis was found to be calciumdependent and occurred over a temperature range of 25 to 37 degrees. However, the Vibrio pommerensis sp. nov. strain CH-291 was not pathogenic for eels and not toxic for Vero cells.Because hemolysins are major virulence factors of the genus Vibrio and the encoding genes have been found to be useful markers in molecular diagnostic procedures, the hemolysisencoding genes of the new species were investigated. From a genomic library constructed from strain CH-291, a cloned chromosomal DNA fragment of 15.6 kbp conferred hemolysis on enterohemolysin agar plates over the same temperature range to a strain of Escherichia coli DH5a. harboring a plasmid (pVH) containing this fragment. Hybridization studies showed the cloned sequence to be unique to Vibrio pommerensis sp. nov. strains with no similarities to known bacterial cytolysins. Subcloning of fragments of the 15.6 kbp egion from plasmid pVH yielded three different DNA regions able to confer hemolytic activity to transformants of E. coli. These three regions were cloned in the plasmids pVHH, pVH2H and pVH2E. The hemolysin gene of the plasmid pVHH encoded a membrane-associated protein of 630 amino acids, which resulted in a hemolysis. The hemolysin gene of the plasmid pVH2H would encode a protein of 261 amino acids. The hemolysin-coding region in the plasmid pVH2E has not yet been identified.The cloned 15.6 kbp DNA-Fragment possessed structural features typical for genetic islands, including a decreased G + C-content, a flanking cryptic IS-element and the occurence of a hemolysin gene. Due to the unique occurrence of the hemolysis-encoding DNA region to Vibrio pommerensis sp. nov. strains as shown by hybridisation experiments, the latter region may provide a useful marker for the identification of Vibrio pommerensis sp. nov. strains.