Counter-defense mechanisms and phylogeny of a novel Tunavirus phage

The global rise of antibiotic resistance has renewed interest in bacteriophages as alternative therapeutics, yet bacterial immune defenses often limit their effectiveness. Here, we describe a newly isolated Escherichia coli phage, Ec_Ou_ZC1, which exhibits a high burst size and encodes multiple counter-defense elements, including anti-superinfection exclusion proteins and a conserved intron-encoded HNH endonuclease. Phylogenetic analyses place Ec_Ou_ZC1 within the genus Tunavirus and demonstrate that stepwise phylogenetic reconstruction can effectively predict host range and polyvalence of newly identified phages.