Bacteriophage K1-5 encodes two different tail fiber proteins, allowing it to infect and replicate on both K1 and K5 strains of Escherichia coli

A virulent double-stranded DNA bacteriophage, Phi K1-5, has been isolated a nd found to be capable of infecting Escherichia coli strains that possess e ither the K1 or the K5 polysaccharide capsule. Electron micrographs show th at the virion consists of a small icosohedral head with short tail spikes, similar to members of the Podoviridae family. DNA sequence analysis of the region encoding the tail fiber protein showed two open reading frames encod ing previously characterized hydrolytic phage tail fiber proteins, The firs t is the K5 lyase protein gene of Phi K5, which allows this phage to specif ically infect K5 E, coli strains, A second open reading frame encodes a pro tein almost identical in amino acid sequence to the N-acetylneuraminidase ( endosialidase) protein of Phi K1E, which allows this phage to specifically infect K1 strains off. coli, We provide experimental evidence that mature p hage particles contain both tail fiber proteins, and mutational analysis in dicates that each protein can be independently inactivated. A comparison of the tail gene regions of Phi K5, Phi K1E, and Phi K1-5 shows that the gene s are arranged in a modular or cassette configuration and suggests that thi s family of phages can broaden host range by horizontal gene transfer.