Characterization of novel Erwinia amylovora-specific phiEaSP1 phage and its application as phage cocktail for managing fire blight in apples

Abstract

Erwinia amylovora (Ea) is a devastating bacterial pathogen that causes fire blight disease in Rosaceae family plants, including apples and pears. The use of bacteriophages is an alternative strategy to antibiotics for managing bacterial pathogens. In this study, the Ea-specific virulent phiEaSP1 phage was characterized, and its biocontrol efficacy against Ea was evaluated in apple seedlings. Genomic analyses revealed that phiEaSP1 belongs to the family Chaseviridae, subfamily Cleopatravirinae, and genus Loessnervirus. Most phiEaSP1 particles bound to the host cell surface within 5 min, and one virion made 68 progenies within 20 min of infection. The phage rapidly lysed Ea cells in vitro and maintained its lytic activity after incubation under different environmental conditions, including temperature, pH, and UV-A, as well as in the soil, with surfactants, and on apple seedlings. Receptor analysis using the Tn5 random mutant library of Ea TS3128 demonstrated that phiEaSP1 recognizes lipopolysaccharide as a receptor, whereas phiEaP-8 and phiEaP-21 recognize cellulose as a receptor. Protective efficacy against fire blight was tested on apple seedlings pretreated with the single phiEaSP1 or a phage cocktail containing phiEaSP1, phiEaP-8, and phiEaP-21. No or only weak symptoms were observed in the phage-treated seedlings. The application of a phage cocktail showed better control efficacy, indicating the potential of the phage cocktail, including phiEaSP1, as a preventive agent. Taken together, these results suggest that the use of a phage cocktail containing phiEaSP1 could be a potential strategy for the biocontrol of fire blight disease in apples.