Characterization of a ViI-like Phage Specific to Escherichia coli O157:H7

Abstract

Phage vB_EcoM_CBA120 (CBA120), isolated against Escherichia coli O157:H7 from a cattle feedlot, is morphologically very similar to the classic phage ViI of Salmonella enterica serovar Typhi. Until recently, little was known genetically or physiologically about the ViI-like phages, and none targeting E. coli have been described in the literature. The genome of CBA120 has been fully sequenced and is highly similar to those of both ViI and the Shigella phage AG3. The core set of structural and replication-related proteins of CBA120 are homologous to those from T-even phages, but generally are more closely related to those from T4-like phages of Vibrio, Aeromonas and cyanobacteria than those of the Enterobacteriaceae. The baseplate and method of adhesion to the host are, however, very different from those of either T4 or the cyanophages. None of the outer baseplate proteins are conserved. Instead of T4's long and short tail fibers, CBA120, like ViI, encodes tail spikes related to those normally seen on podoviruses. The 158 kb genome, like that of T4, is circularly permuted and terminally redundant, but unlike T4 CBA120 does not substitute hmdCyt for cytosine in its DNA. However, in contrast to other coliphages, CBA120 and related coliphages we have isolated cannot incorporate 3H-thymidine (3H-dThd) into their DNA. Protein sequence comparisons cluster the putative "thymidylate synthase" of CBA120, ViI and AG3 much more closely with those of Delftia phage φW-14, Bacillus subtilis phage SPO1, and Pseudomonas phage YuA, all known to produce and incorporate hydroxymethyluracil (hmdUra).

Structure and genome release of Twort-like Myoviridae phage with a double-layered baseplate

“…S2 and Table S1, and Movie S2). The double-layered baseplate architecture, which is specific for the contracted tail (Movie S3), is structurally distinct and has been observed in negative-stain micrographs of many Myoviridae phages (5)(6)(7). A characteristic feature of the double-layered baseplate is compact building blocks, which were previously described as thick legs of a "Victorian side table," organized in two concentrical hexamers (8).…”

“…The tripod proteins constitute the narrow tip of the cone and three elongated protrusions that form peripheral regions of the receptor-tripod complex base. Virulence associated proteins VrlC were previously suggested to organize the structures of the doublelayered baseplates (6,8), and may therefore correspond to the tripod proteins. A complex of proteins gp122 and gp123 is a candidate for the phi812 VrlC (SI Appendix, Table S2).…”

Isolation, characterization and complete genome sequence of PhaxI: a phage of Escherichia coli O157 : H7

“…Its genome encodes a DNA polymerase, primase, helicase, ligase, primase-helicase, loader of helicase, clamp loader, sliding clamp, ssDNA-binding protein and topoisomerase subunits. All these genes are present in the genomes of the other six members of the genus 'Viunalikevirus' (Adriaenssens et al, 2012b;Anany et al, 2011;Hooton et al, 2011;Kutter et al, 2011;Park et al, 2012). These proteins have highest similarities with proteins of phages SFP10, CBA120 and PhiSH19, and lowest with AG3 and LIMEstone1.…”

“…Previous studies resulted in isolating several lytic O157 : H7 coliphages such as PP01, e11/2, e4/1c, CEV1, KH1, KH4, KH5, SH1, AKFV33, rv5, wV8, AR1, SFP10 and CBA120 (Kudva et al, 1999;Kutter et al, 2011;Liao et al, 2011;Morita et al, 2002;Niu et al, 2012;O'Flynn et al, 2004;Park et al, 2012;Raya et al, 2006;Sheng et al, 2006;Villegas et al, 2009). Some of them lyse both E. coli O157 : H7 and other pathogens of the family Enterobacteriaceae.…”

“…Similarly to phages vB_EcoM_CBA120 and phiSboM-AG3, no holin or lysin genes were directly identified in the PhaxI genome (Anany et al, 2011;Kutter et al, 2011). Class I holins possess 95 aa or more with three transmembrane (TM) domains and class II holins have 65-95 residues with two TM domains (Young et al, 2000).…”