Bacteriophage: An Unusual Hybrid of Serologically Unrelated Phages P22 and P221
Nobuto Yamamoto 1
1 Laboratory of Biophysics and Biochemistry, Division of Biologics Standards, National Institutes of Health, Bethesda 14, Maryland
Serologically unrelated bacteriophages P22 and P221 that grow on Salmonella typhimurium are described. The phage P22 and a mutant P22h have short tails with hexagonal base plates, whereas P221 has a long, flexible tail without a base plate. P22h and P221 can recombine to exchange genetic markers. In the course of the recombination experiment, an unusual hybrid, P22-221Hy, was found. It mutates to P221 and P22S at a frequency of 10-4 and 1O-5, respectively. Unlike P22h, P22S gives clear plaques on both S. typhimurium, St, and its mutant, St/22, but is morphologically and serologically indistinguishable from P22 and P22h. The use of single-clone technique on P22-221Hy proved that a P22-221Hy genome consists of a P22h and a P221 genome and is carried by the P22h capsid. However, it seems probable that the information for synthesizing the P221 capsid may be suppressed by the information for synthesizing the P22h capsid. P22-221Hy is a stable hybrid rather than a heterozygote, because it does not segregate by passing through host cells. Thus,, one bacteriophage can carry the genetic information for two distinct bacteriophages.
