The ability of agriculture to continually provide food to a growing world population is of crucial importance. Bacterial diseases of plants and animals have continually reduced production since the advent of crop cultivation and animal husbandry practices. Antibiotics have been used extensively to mitigate these losses. The rise of antimicrobial resistant (AMR) bacteria, however, together with consumers’ calls for antibiotic-free products, presents problems that threaten sustainable agriculture. Bacteriophages (phages) are proposed as bacterial population control alternatives to antibiotics. Their unique properties make them highly promising but challenging antimicrobials. The use of phages in agriculture also presents a number of unique challenges. This mini-review summarizes recent development and perspectives of phages used as antimicrobial agents in plant and animal agriculture at the farm level. The main pathogens and their adjoining phage therapies are discussed.

The first complete genome sequence for a myoviridal bacteriophage, ΦEa21-4, infecting Erwinia amylovora, Erwinia pyrifoliae , and Pantoea agglomerans strains has been determined. The unique sequence of this terminally redundant, circularly permuted genome is 84,576 bp. The ΦEa21-4 genome has a GC content of 43.8% and contains 117 putative protein-coding genes and 26 tRNA genes. ΦEa21-4 is the first phage in which a precisely conserved rho-independent terminator has been found dispersed throughout the genome, with 24 copies in all. Also notable in the ΦEa21-4 genome are the presence of tRNAs with six- and nine-base anticodon loops, the absence of a small packaging terminase subunit, and the presence of nadV , a principle component of the NAD ⁺ salvage pathway, which has been found in only a few phage genomes to date. ΦEa21-4 is the first reported Felix O1-like phage genome; 56% of the predicted ΦEa21-4 proteins share homology with those of the Salmonella phage. Apart from this similarity to Felix O1, the ΦEa21-4 genome appears to be substantially different, both globally and locally, from previously reported sequences. A total of 43 of the 117 genes are unique to ΦEa21-4, and 32 of the Felix O1-like genes do not appear in any phage genome sequences other than ΦEa21-4 and Felix O1. N-terminal sequencing and matrix-assisted laser desorption ionization-time of flight analysis resulted in the identification of five ΦEa21-4 genes coding for virion structural proteins, including the major capsid protein.

Fire blight, a disease of pome fruits caused by the bacterium Erwinia amylovora, has become increasingly difficult to manage after the emergence of streptomycin-resistant strains. Alternative antibiotics and copper are available; however, these chemicals have use restrictions in some countries and also can carry risks of phytotoxicity. Therefore, there is growing interest in biological-based management options, with bacteriophage (phages) showing promise, as these naturally occurring pathogens of bacteria are easy to isolate and grow. However, there are several technical challenges regarding the implementation of phage biocontrol in the field, as the viral molecules suffer from ultraviolet radiation (UVR) degradation and can die off rapidly in the absence of the host bacterium. In this work, we assessed the efficacy of Erwinia phages and a commercial phage product for blossom blight control in the field across multiple locations in the eastern United States. In these tests, disease control ranged from 0.0 to 82.7%, and addition of a UVR protectant only resulted in significantly increased disease control in 2 of 12 tests. We also analyzed microbial community population changes in response to phage application. Changes in bacterial community diversity metrics over time were not detected; however, relative abundances of target taxa were temporarily reduced after phage applications, indicating that these phage applications did not have deleterious effects on the flower microbiome. We have demonstrated that biological control of fire blight with phages is achievable, but a better understanding of phage−pathogen dynamics is required to optimize disease control efficacy.

The complete genome of an Erwinia amylovora bacteriophage, vB_EamM_Ea35-70 (Ea35-70), is 271,084 bp, encodes 318 putative proteins, and contains one tRNA. Comparative analysis with other Myoviridae genomes suggests that Ea35-70 is related to the Phikzlikevirus genus within the family Myoviridae , since 26% of Ea35-70 proteins share homology to proteins in Pseudomonas phage φKZ.

Erwinia amylovorais an economically significant agricultural pathogen found throughout the world. In North America,E. amylovorahas developed streptomycin resistance and therefore alternative treatments using phages have received increased attention.

Summary: Lytic bacteriophages are in development as biological control agents for the prevention of fire blight disease caused by E rwinia amylovora . Temperate phages should be excluded as biologicals since lysogeny produces the dual risks of host resistance to phage attack and the transduction of virulence determinants between bacteria. The extent of lysogeny was estimated in wild populations of E . amylovora and P antoea agglomerans with real–time polymerase chain reaction primers developed to detect E . amylovora phages belonging to the M yoviridae and P odoviridae families. P antoea agglomerans , an orchard epiphyte, is easily infected by E rwinia spp. phages, and it serves as a carrier in the development of the phage‐mediated biological control agent. Screening of 161 E . amylovora isolates from 16 distinct geographical areas in N orth A merica, E urope, N orth A frica and N ew Z ealand and 82 P . agglomerans isolates from southern O ntario, C anada showed that none possessed prophage. Unstable phage resistant clones or lysogens were produced under laboratory conditions. Additionally, a stable lysogen was recovered from infection of bacterial isolate Ea110R with P odoviridae phage ΦEa35‐20. These laboratory observations suggested that while lysogeny is possible in E . amylovora , it is rare or absent in natural populations, and there is a minimal risk associated with lysogenic conversion and transduction by E rwinia spp. phages.