Bacteriophage K1-5 Encodes Two Different Tail Fiber Proteins, Allowing It To Infect and Replicate on both K1 and K5 Strains of Escherichia coli

Abstract

A virulent double-stranded DNA bacteriophage, ⌽K1-5, has been isolated and found to be capable of infecting Escherichia coli strains that possess either the K1 or the K5 polysaccharide capsule. Electron micrographs show that 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 encoding previously characterized hydrolytic phage tail fiber proteins. The first is the K5 lyase protein gene of ⌽K5, which allows this phage to specifically infect K5 E. coli strains. A second open reading frame encodes a protein almost identical in amino acid sequence to the N-acetylneuraminidase (endosialidase) protein of ⌽K1E, which allows this phage to specifically infect K1 strains of E. coli. We provide experimental evidence that mature phage particles contain both tail fiber proteins, and mutational analysis indicates that each protein can be independently inactivated. A comparison of the tail gene regions of ⌽K5, ⌽K1E, and ⌽K1-5 shows that the genes are arranged in a modular or cassette configuration and suggests that this family of phages can broaden host range by horizontal gene transfer.Escherichia coli capsular polysaccharides (K antigens) have often been associated with increased virulence (17). The K1 antigen in particular increases the invasiveness of E. coli, and these strains are often involved in cases of meningitis and septicemia (32). These polysaccharide coats also act as recognition sites for bacteriophages, which often carry tail spikes that contain polysaccharide depolymerization activities. Several K1-specific phages have been described (10), one of which, ⌽K1E, was found to possess N-acetylneuraminidase (endosialidase) as a part of the tail fiber protein (37). This enzyme catalyzes the cleavage of ␣-2,8-linked poly-N-acetylneuraminic acid carbohydrate polymer of the K1 capsule. It has been suggested that the tail fiber protein is involved in both adsorption to the cell surface and penetration into the cell by enzymatically degrading the polysaccharide capsule. The ⌽K1E endosialidase gene has been cloned and sequenced (20). A similar gene has been cloned and sequenced from ⌽K1F (29).⌽K5 is a related bacteriophage specific for E. coli strains that display the K5 antigen, a polymer consisting of a repeating structure of 4-linked ␣-N-acetylglucosamine and ␤-glucuronic acid (N-acetyl heparosin). In this case, ⌽K5 encodes a tailassociated K5 specific lyase protein that is also responsible for attachment to the cell surface and degradation of the K5 polysaccharide capsule (12,14). Phage specific for other E. coli polysaccharide antigens, including K3, K7, K12, K13, and K20 (26, 27), have also been found; all probably possess specific polysaccharide depolymerization activities as part of the phage particle.Both ⌽K5 and ⌽K1E have a Salmonella phage SP6-like promoter upstream of their tail proteins as well as a region of homology which is just downstream of the...

The K5 Lyase KflA Combines a Viral Tail Spike Structure with a Bacterial Polysaccharide Lyase Mechanism

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Phage therapy: the Escherichia coli experience

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Proteolytic Processing and Oligomerization of Bacteriophage-derived Endosialidases

“…For endoNE of K1E, hetero-oligomeric structures of 208 and 325 kDa were described, composed of endoNE and a not as yet identified 38-kDa protein (8,18). So far, genes encoding endosialidases have been cloned from four different phages: K1F (11), K1E (18,19), 63D (GenBank accession number AB015437), and the dual specificity phage K1-5 that can infect E. coli K1 and K5 (20). However, recombinant expression of active enzyme has been reported only in the case of endoNE (18,19).…”