Characterization of Erwinia amylovora specific bacteriophages

Erwinia amylovora (Ea), the causal agent of fire blight, is one of the most destructive pathogens of pome fruits worldwide. Biological approach in the disease control might be potential solution for poor efficacy of available bactericides. Therefore, we isolated bacteriophages specific to this bacterium and studied their characteristics and diversity. Eleven bacteriophage strains specific to Ea were isolated from rhizosphere, irrigation water or symptomless pear and apple leaves. Based on their lytic activity, eight strains were chosen for further characterization by studying their host specificity, plaque and virion morphology and genome properties using PCR, RAPD-PCR and RFLP analysis. All phages lysed 70 Ea strains originating from Serbia, isolated from apple, pear, quince, Japanese pear, medlar, Cotoneaster sp., and Sorbus sp. They produced clear or moderately clear plaques on bacterial lawn of different Ea strains after 24 h of incubation. Examination by transmission electron microscopy indicated that all eight phages belong to the order Caudovirales, the tailed phages, including the members of the families Myoviridae (6 strains) and Siphoviridae (2 strains). Based on phage DNA digestion using seven restriction endonucleases and RAPD-PCR (primers A9, R13, A10) phages were differentiated into two groups. In PCR assay using primers for Ea phages detection (Pun45), specific fragment of three phages was amplified. Although all studied phages showed the same host range, they have been differentiated based on virion morphology and genetic properties, indicating diversity within studied population