Characterization of bacteriophage φPto-bp6g, a novel phage that lyses Pseudomonas tolaasii causing brown blotch disease in mushrooms.

The bacteriophage, φPto-bp6g, exhibited strong bactericidal activity against Pseudomonas tolaasii, the bacterium that causes brown blotch disease in cultivated mushrooms. Analysis of phage morphology with an electron microscope revealed that φPto-bp6g contains an icosahedral head and a long tail, which is classified as the family of Siphoviridae. The phage was observed to lyse P. tolaasii in the broth about 4h after inoculation, indicating a putative lytic pathway exists during bacterial growth. The whole genome of φPto-bp6g was completely sequenced, with a length of 26,499 bp and a G+C content of 42.7%. A total of 77 open reading frames (ORFs) as putative coding sequences were identified and annotated, whereas 43 ORFs possessed no homologs. Proteins of several ORFs showed similarity with proteins of a diverse group of phages, including Siphoviridae (5 ORFs), Myoviridae (11 ORFs), and Podoviridae (4 ORFs). Phage proteins were grouped into three categories based on their predicted functions: (i) DNA replication and nucleotide metabolism, (ii) phage particle formation, and (iii) host interaction. Since there is no identified gene encoding integrase and toxins in phage genome, phage φPto-bp6g could be potentially applicable as a safe biological control reagent against brown blotch disease in mushroom cultivation.