Genomic Analysis of Two Cold-Active <i>Pseudoalteromonas</i> Phages Isolated from the Continental Shelf in the Arctic Ocean

Cold-active bacteriophages are bacterial viruses that infect and replicate at low temperatures (≤4 °C). Understanding remains limited of how cold-active phage–host systems sustain high viral abundance despite the persistently low temperatures in pelagic sediments in polar seas. In this study, two <i>Pseudoalteromonas</i> phages, ACA1 and ACA2, were isolated from sediment core samples of the continental shelf in the western Arctic Ocean. These phages exhibited successful propagation at a low temperature of 1 °C and displayed typical myovirus morphology with isometric icosahedral heads and contractile tails. The complete genome sequences of phages ACA1 and ACA2 were 36,825 bp and 36,826 bp in size, respectively, sharing almost the same gene content. These are temperate phages encoding lysogeny-related proteins such as anti-repressor, immunity repressor and integrase. The absence of cross-infection between the host strains, which were genomically distinct <i>Pseudoalteromonas</i> species, can likely be attributed to heavy divergence in the anti-receptor apparently mediated by an associated diversity-generating retroelement. HHpred searching identified genes for all of the structural components of a P2-like phage (family <i>Peduoviridae</i>), although the whole of the <i>Peduoviridae</i> family appeared to be divided between two anciently diverged tail modules. In contrast, Blast matching and whole genome tree analysis are dominated by a nonstructural gene module sharing high similarity with <i>Pseudoalteromonas</i> phage C5a (founder of genus <i>Catalunyavirus</i>). This study expands the knowledge of diversity of P2-like phages known to inhabit <i>Peudoalteromonas</i> and demonstrates their presence in the Arctic niche.