Isolation and characterization of lytic bacteriophages infecting Pectobacterium atrosepticum

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 sewage water and bulk soil samples collected in the cities Wuhan and Datong in China. Three lytic bacteriophages were obtained and named Pectobacterium Phages 1, 2, and 7 (PP1, 2 and 7). Transmission electron microscopic analysis revealed that PP1 and PP7 were similar in size with a head diameter (ca. 70–80 nm, n = 10), and PP2 had a smaller head size (ca. 50 nm, n = 10). PP2 and PP7 had a short tail, and no tail was observed for PP1. 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 mixing. The potential of these bacteriophages to protect potato seedlings was tested. After 27 days of inoculation, seedlings inoculated with water and those sprayed with phages alone exhibited healthy growth with no symptoms. Conversely, seedlings solely inoculated with P. a. displayed a significantly lower survival rate compared to the water-inoculated seedlings. However, seedlings co-inoculated with P. a. and single or mixed phages showed a substantial improvement in survival rates by 33% and 30%, respectively, compared to the group without phage treatment.