Isolation and characterization of lytic bacteriophages infecting Pectobacterium atrosepticum

Abstract

Abstract Pectobacterium spp. cause blackleg and soft rot on potato worldwide. Potato is a staple crop in China, and blackleg and soft rot diseases caused by Pectobacterium spp. have increased significantly as potato cultivation expanded rapidly in the last decade. This study was conducted to isolate and characterize the lytic bacteriophages infecting the major pathogen causing potato blackleg and soft rot, Pectobacterium atrosepticum (P. a.), in water and soil samples collected in the cities Wuhan and Datong in China. Three lytic bacteriophages were obtained and named Pectobacterium Phages ZRIMU1, 2, and 7. Transmission electron microscopic analysis revealed that all three phages were similar in size, with a smooth head (diameter ca. 40–50 nm) and without a neck or tail. The adsorption of phages PP1, PP2, and PP7 to P. a. after 18, 27, and 18 min was 98, 99 and 98%, respectively. The latent periods for PP1, PP2, and PP7 were 20, 40, and 50 min, respectively. In vitro bacterial challenge assays showed that these three phages were able to infect P. a. 1 h after coinoculation. The potential of these bacteriophages to protect potato seedlings was tested. After 27 days of inoculation, seedlings inoculated with water and sprayed with or without phages developed well, and no symptoms developed. Seedlings inoculated with P. a. only had a significantly lower survival rate than the controls, and seedlings coinoculated with P. a. and phages significantly improved the survival rate by 40%. Recovery of symptomatic plants was observed in groups that were treated with either a single phage or a mixture of phages. More investigations are needed to clarify the mechanism by which phages can be used to cure symptomatic potato plants.