Molecular analysis of the low-temperature Escherichia coli phage vB_EcoS_NBD2.

A novel low-temperature Escherichia coli phage vB_EcoS_NBD2 was isolated in Lithuania from agricultural soil. With an optimum temperature for plating around 20 °C, vB_EcoS_NBD2 efficiently produced plaques on Escherichia coli NovaBlue (DE3) at a temperature range of 10-30 °C, yet failed to plate at temperatures above 35 °C. Phage vB_EcoS_NBD2 virions have a siphoviral morphology with an isometric head (65 nm in diameter), and a non-contractile flexible tail (170 nm). The 51,802-bp genome of vB_EcoS_NBD2 has a G + C content of 49.8%, and contains 87 probable protein-encoding genes as well as 1 gene for tRNA. Comparative sequence analysis revealed that 22 vB_EcoS_NBD2 ORFs encode unique proteins that have no reliable identity to database entries. Based on homology to biologically defined proteins and/or proteomics analysis, 36 vB_EcoS_NBD2 ORFs were given a putative functional annotation, including 20 genes coding for morphogenesis-related proteins and 13 associated with DNA metabolism. Phylogenetic analysis revealed that vB_EcoS_NBD2 belongs to the subfamily Tunavirinae, but cannot be assigned to any genus currently recognized by ICTV.