Bacteriophage YeO3-12 is a lytic phage of Yersinia enterocolitica serotype O:3. The phage receptor is the lipopolysaccharide O chain of this serotype that consists of the rare sugar 6-deoxy-L-altropyranose. A one-step growth curve of YeO3-12 revealed eclipse and latent periods of 15 and 25 min, respectively, with a burst size of about 120 PFU per infected cell. In electron microscopy YeO3-12 virions showed pentagonal outlines, indicating their icosahedral nature. The phage capsid was shown to be composed of at least 10 structural proteins, of which a protein of 43 kDa was predominant. N-terminal sequences of three structural proteins were determined, two of them showing strong homology to structural proteins of coliphages T3 and T7. The phage genome was found to consist of a double-stranded DNA molecule of 40 kb without cohesive ends. A physical map of the phage DNA was constructed using five restriction enzymes. The phage infection could be effectively neutralized using serum from a rabbit immunized with whole YeO3-12 particles. The antiserum also neutralized T3 infection, although not as efficiently as that of YeO3-12. YeO3-12 was found to share, in addition to the N-terminal sequence homology, several common features with T3, including morphology and nonsubjectibility to F exclusion. The evidence conclusively indicated that YeO3-12 is the first close relative of phage T3 to be described.Yersinia enterocolitica is a Gram-negative species which contains several serotypes, some of which are pathogenic to humans. The major pathogens in Europe, Canada, Japan, and South Africa belong to serotypes O:3 and O:9, and those in the United States belong to serotype O:8 (11). The main reservoir in nature for Y. enterocolitica is pigs (15), and human infections usually take place after ingestion of contaminated foodstuffs.A number of yersiniophages have been described, but only a few have been characterized by electron microscopy and to our knowledge none have been studied in detail. In our laboratory a number of Yersinia-specific bacteriophages have been isolated, all originating from the raw incoming sewage of the Turku City sewage treatment plant, and the phages have been used as genetic tools (32). One of the phages, YeO3-12, was isolated as specific to Y. enterocolitica serotype O:3. The phage could infect Escherichia coli C600 expressing the cloned O antigen of Y. enterocolitica serotype O:3 and spontaneous phage-resistant Y. enterocolitica serotype O:3 strains were missing the O antigen, indicating that the O antigen is the phage receptor (4, 5). The serotype O:3 specificity makes the phage YeO3-12 a potential biotechnological tool, and therefore we have initiated its detailed characterization. Here we present the biological and physical properties of the phage and evidence suggesting that YeO3-12 is closely related to coliphages T3 and T7. MATERIALS AND METHODSCulture conditions. Bacterial strains, bacteriophages and plasmids used in this study are listed in Table 1. Virulence plasmid-cured Y. enterocolitica serotyp...

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Yersiniophage wR1-37 is a tailed bacteriophage having a 270 kb DNA genome with thymidine replaced by deoxyuridine Bacteriophage wR1-37 was isolated based on its ability to infect strain YeO3-R1, a virulenceplasmid-cured O antigen-negative derivative of Yersinia enterocolitica serotype O : 3. In this study, the phage receptor was found to be a structure in the outer core hexasaccharide of Y. enterocolitica O : 3 LPS. The phage receptor was present in the outer core of strains of many other Y. enterocolitica serotypes, but also in some Yersinia intermedia strains. Surprisingly, the receptor structure resided in the O antigen of Yersinia pseudotuberculosis O : 9. Electron microscopy demonstrated that wR1-37 particles have an icosahedral head of 88 nm, a short neck of 10 nm, a long contractile tail of 236 nm, and tail fibres of at least 86 nm. This implies that the phage belongs to the order Caudovirales and the family Myoviridae in the ICTV (International Committee for Taxonomy of Viruses) classification. wR1-37 was found to have a lytic life cycle, with eclipse and latent periods of 40 and 50 min, respectively, and a burst size of~80 p.f.u. per infected cell. Restriction digestions and PFGE showed that the wR1-37 genome was dsDNA and~270 kb in size. Enzymically hydrolysed DNA was subjected to HPLC-MS/MS analysis, which demonstrated that the wR1-37 genome is composed of DNA in which thymidine (T) is >99 % replaced by deoxyuridine (dU). The only organisms known to have similar DNA are the Bacillus subtilis-specific bacteriophages PBS1 and PBS2. N-terminal amino acid sequences of four major structural proteins did not show any similarity to (viral) protein sequences in databases, indicating that close relatives of wR1- 37 have not yet been characterized. Genes for two of the structural proteins, p24 and p46, were identified from the partially sequenced wR1-37 genome. INTRODUCTIONYersinia enterocolitica is a Gram-negative bacterium of the family Enterobacteriaceae. The species includes over 30 serotypes, a number of which are human pathogens (Wauters et al., 1991). While the major pathogenic serotypes in Europe, Canada, Japan and South Africa are O : 3 and O : 9; in the United States serotype O : 8 is more prevalent. Y. enterocolitica is widely distributed in nature, swine being the major reservoir of the pathogenic strains (Bottone, 1997).Bacteriophages are the most abundant organisms on Earth, and it is estimated that for each microbial isolate at least 10 different phages can be found (Hendrix, 2002;Pedulla et al., 2003). A number of phages infecting the members of the genus Yersinia have been isolated (Baker & Farmer, 1982;Popp et al., 2000;Stevenson & Airdrie, 1984), but relatively few have been characterized in more detail. Y. enterocolitica O : 3-specific phage wYeO3-12 has been shown to be closely related to Escherichia coli phages T3 and T7 (Pajunen et al., 2000(Pajunen et al., , 2001. Likewise, Yersinia pestis phage wA1122 was recently found to be a close relative of T7 (Garcia et al., 2003a). Bacteriophage...