Conversion of Vibrio eltor MAK757 to classical biotype: role of phage PS166

Temperate phage PS166 infection of Vibrio eltor MAK757 resulted in complete changes in all biotype-specific determinants. About 10% of the PS166 lysogens of MAK757 lost their eltor-specific determinants, namely, the ability to produce soluble hemolysin, cell-associated hemagglutinin for chicken erythrocytes, and resistance to polymyxin B, as well as resistance to Mukherjee's group IV phage and sensitivity to eltor phage e4. These lysogens were found to have acquired the properties of classical strains, most significantly becoming sensitive to group IV phage but resistant to eltor-specific e4. The remainder of these lysogens, however, retained their parental biotype and serotype but acquired auxotrophy for glycine and histidine. The differential behavior of the two types of lysogen was due to the integration of the phage PS166 genome at different locations in the host chromosome. A 800-bp BglII fragment was found to contain the attP site. Phage PS166 has a polyhedral head (95 nm in diameter) and a contractile tail (98 nm in length). The phage chromosome is a linear double-stranded DNA of 110 kb and a G + C content of 58.7%.