Isolation and Complete Sequence of One Novel Marine Bacteriophage PHS21 Infecting Pseudoalteromonas marina.

PHS21 against Pseudoalteromonas is isolated from Qingdao offshore seawater. The phage was characterized and identified by morphological examination, stability, whole genome sequencing, and bioinformatics analysis. Morphological analysis of PHS21 by transmission electron microscopy shows that belonged to the Siphoviridae family. PHS21 showed strong tolerance with a wide range of temperatures and pH. One-step growth assay indicates that the latent period is about 48 min and the burst size is approximately 218 PFU/cell (plaque forming unit/cell). Its complete genomic sequence is 35,802-bp long with 50 putative open reading frames. Phage PHS21 and PHS3 displayed a very close evolutionary relationship; however, having different DNA packaging proteins indicates that they may have already evolved distinct ways to package DNA in host cells. This study provides the detailed description and genomic characterization of a novel Pseudoalteromonas phage.