Lytic phages isolated from Egypt for biocontrol of potato soft rot caused by Pectobacterium carotovorum

Abstract

Pectobacterium carotovorum is an economically important phytopathogen causing destructive bacterial soft rot disease in many ornamental plants and fruit and vegetable crops worldwide, including potato. Phage therapy is a promising and environmentally safe alternative to combat bacterial diseases either in the field or during storage. In this study, we characterized two novel P. carotovorum-specific phages, designated PcaP1EGY and PcaP2EGY, isolated from soil in Egypt. We also sequenced the genomes of the two phages, which are the first two complete genome sequences determined for P. carotovorum-infecting podoviruses from Egypt. Phages PcaP1EGY and PcaP2EGY have a high phage titer of 1012 PFU/mL and growth characteristics of an exclusively lytic life cycle. Both phages displayed specificity to and visible lysis activity against all four tested strains of P. carotovorum. They both had a latent period of 30 min and a high burst size of approximately 599 PFU/infected cell for PcaP1EGY and 570 for PcaP2EGY. Additionally, they exhibited remarkable survivability under a wide range of pH, temperature, salt concentration and UV exposure conditions. Both phages, when used alone or in combination, significantly reduced in vitro growth of P. carotovorum after 4 h at all tested multiplicity of infection. Phages PcaP1EGY and PcaP2EGY offered significant protection for both potato tubers and potato plants against soft rot disease caused by P. carotovorum in both our tuber maceration test and greenhouse pot experiment as compared to tubers/plants inoculated with P. carotovorum without receiving any phage treatment. Our results suggest that phages PcaP1EGY and PcaP2EGY have great biocontrol potential against potato soft rot disease caused by P. carotovorum either in the field or during storage after harvest.