Isolation and characteristics of new phages from a serine-producing Escherichia coli K-12

Abstract Two lytic phages, designated S1 and S2, were isolated from culture lysates of a genetically modified serine-producing Escherichia coli K-12. Both phages were highly species-specific for E. coli . S1 was specific for strains of K-12, while S2 attacked strains B and C in addition to K-12 strains. S1 had an icosahedral head 75 nm in diameter and a contractile tail 150 nm long. S2 had an icosahedral head 60 nm in diameter and a noncontractile tail 160 nm long. They were serologically unrelated. Their serotypes were different from those of the other E. coli phages. The latent period and burst size were 28 min and 450, respectively, for S1, and 15 min and 100, respectively, for S2. The phages contained double-stranded DNA with four normal bases. The G+C contents were about 31% for S1 DNA and about 37% for S2 DNA. Restriction patterns of their DNAs were different from each other. The genome sizes were 52 kbp for S1 and 49 kbp for S2. No homology was observed between their genomes. Furthermore, the structural proteins of the two phages also differend. W conclude that phages S1 and S2, differing from each other, could be new phages for E. coli .