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A proposed new genus of the family Myoviridae, "rV5-like viruses", includes two lytic bacteriophages: Escherichia coli O157: H7-specific bacteriophage rV5 and Salmonella phage PVP-SE1. Here, we present basic properties and genomic characterization of a novel rV5-like phage, vB_EcoM_FV3, which infects E. coli K-12-derived laboratory strains and replicates at high temperature (up to 47 °C). The 136,947-bp genome of vB_EcoM_FV3 contains 218 open reading frames and encodes 5 tRNAs. The genomic content and organization of vB_EcoM_FV3 is more similar to that of rV5 than to PVP-SE1, but all three phages share similar morphological characteristics and form a homogeneous phage group.

Bacteriophages vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20, showing an unusual low-temperature plating profile and producing constantly growing plaques, were isolated from aquatic environments of Lithuania. Although vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20 resembled phage T4 both in their genome size and in their major structural protein (gp23) pattern, physiological properties of all three phages tested differed significantly from those of T4. With an optimum temperature for plating around 24 degrees C and a high efficiency of plating in the range 7-30 degrees C, bacteriophages vB_EcoM-VR7 and vB_EcoM-VR20 failed to plate at 37 degrees C, whereas phage vB_EcoM-VR5 could not be plated at 40 degrees C. Sequence analysis of diagnostic g23 PCR products revealed that g23 of vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20 differed from the corresponding T4 g23 DNA sequence by 21, 21 and 20%, respectively.

The complete genome sequence of the T4-related low-temperature Escherichia coli bacteriophage vB_EcoM-VR7 was determined. The genome sequence is 169,285 bp long, with a G+C content of 40.3%. Overall, 95% of the phage genome is coding. It encodes 293 putative protein-encoding open reading frames (ORFs) and tRNA(Met). More than half (59%) of the genomic DNA lacks significant homology with the DNA of T4, but once translated, 72% of the vB_EcoM-VR7 genome (211 ORFs) encodes protein homologues of T4 genes. Overall, 46 vB_EcoM-VR7 ORFs have no homologues in T4 but are derived from other T4-related phages, nine ORFs show similarities to bacterial or non-T4-related phage genes, and 27 ORFs are unique to vB_EcoM-VR7. This phage lacks several T4 enzymes involved in host DNA degradation; however, there is extensive representation of the DNA replication, recombination and repair enzymes as well as the viral capsid and tail structural genes.