Characterization of a Novel <i>Pseudomonas psychrophila</i> Phage P-2FD and Its Endolysin

<i>Pseudomonas</i> is a common food spoilage bacterium that can cause spoilage of milk, eggs, fish, and other food products under low temperature conditions. In this study, a total of four <i>Pseudomonas</i> phages were isolated from spoiled fish and shrimp, and the biological characterization of one of them, <i>Pseudomonas psychrophila</i> phage P-2FD, which exhibited a wider host spectrum, was carried out. Morphological analyses showed that phage P-2FD belonged to the <i>Podoviridae</i> family and the <i>Caudovirales</i> order. When the multiplicity of infection (MOI) was 1000, the growth of <i>P. psychrophila</i> was almost completely inhibited before 9 h. When phage P-2FD treated <i>P. psychrophila</i> in grass carp with an MOI of 1000, the bacterial counts were reduced by 1.77 log₁₀ CFU/g compared with the control group at 4°C for 96 h, indicating that phage P-2FD effectively inhibited the growth of <i>P. psychrophila</i>. Genomic analysis showed that P-2FD was a novel phage, and the whole genome length of P-2FD was 40,453 bp with 42 open reading frames (ORFs). The phage endolysin LysP-2FD was expressed in <i>Escherichia coli</i> BL21 (DE3) and purified, and the lytic rate against <i>P. psychrophila</i> was 78.17% at a concentration of 20 μmol/L. The present study suggests that phage P-2FD and endolysin can be used as potential antimicrobial agents for the control of <i>P. psychrophila</i> in the food industry.