A novel freshwater cyanophage with an unknown source endonuclease VII gene

Cyanophages influence genomic diversity and evolutionary trajectories of both hosts and phages through horizontal gene transfer mechanisms. In this study, a novel cyanophage, designated PP-DH22, was isolated from East Lake in Wuhan, China. This cyanophage demonstrated lytic activity against Plectonema boryanum IU594 and Phormidium foveolarum IU427, and it could form circular plaque with blurred boundary on the plate of IU594. Genomic analysis revealed that PP-DH22 shared similarities with the previously reported cyanophage PP since 2002, including an endonuclease VII gene in the genome of cyanophage PP-DH22 at ORF 32. However, a pivotal difference was discerned in its ORF 39 gene; this gene exhibited a relatively high sequence identity (45.65%) to the endonuclease VII gene of the Escherichia coli phage HZP2, in stark contrast to the relative low identity observed when compared to the cyanophage PP. This notable genetic difference suggests that the endonuclease VII gene of cyanophage PP-DH22 may originate from an unknown source.