Characteristics and whole-genome analysis of a novel Pseudomonas syringae pv. tomato bacteriophage D6 isolated from a karst cave

Pseudomonas syringae is a gram-negative plant pathogen that generally infects plants such as tomato and threatens global crop production. In this study, a novel lytic phage (named Pseudomonas phage D6) infecting P. syringae pv. tomato DC3000 was isolated from the karst cave sediments and characterized. The latent period of phage D6 was shown to be 60 min, and the burst size was 16 plaque forming units/cell. Phage D6 was stable at 30 − 40°C and lost infectivity after heated to 70°C. The infectivity of phage D6 was unaffected at pH 6 − 10, but was inactivated at pH ≤ 5 or ≥ 12. The genome of phage D6 is a linear double-stranded DNA of 307,402 bp with a G + C content of 48.43%. It showed low similarity to known phage genomes in the GenBank database and Viral sequence database. Genomic and phylogenetic analyses revealed that phage D6 is a newly discovered phage. A total of 410 open reading frames (ORFs) and 14 tRNAs were predicted in the genome, 92 of which encode for proteins with predicted functions. In conclusion, the lytic phage D6 identified in this study belongs to a novel phage of the class Caudoviricetes, and has potential application in biological control of plant diseases.