Isolation and Characterization of a Bacteriophage Preying an Antifungal Bacterium

Abstract

Several Bacillus species were isolated from rice field soils, and 16S rRNA gene sequence analysis showed that Bacillus cereus was the most abundant. A strain named BC1 showed antifungal activity against Rhizoctonia solani. Bacteriophages infecting strain BC1 were isolated from the same soil sample. The isolated phage PK16 had an icosahedral head of 100 ± 5 nm and tail of 200 ± 5 nm, indicating that it belonged to the family Myoviridae. Analysis of the complete linear dsDNA genome revealed a 158,127-bp genome with G + C content of 39.9% comprising 235 open reading frames as well as 19 tRNA genes (including 1 pseudogene). Blastp analysis showed that the proteins encoded by the PK16 genome had the closest hits to proteins of seven different bacteriophages. A neighbor-joining phylogenetic tree based on the major capsid protein showed a robust clustering of phage PK16 with phage JBP901 and BCP8-2 isolated from Korean fermented food.

Keywords: Bacillus; Myoviridae; antifungal; interaction; multifactorial.

Fig. 1

Antifungal activity of Bacillus cereus isolated from a rice field. B. cereus BC1, Burkolderia pyrrocinia CH-67 (positive control), and Escherichia coli DH5α (negative control) were simultaneously inoculated with Rhizoctonia solani on potato dextrose agar plates. The plate is a representative from three replications and 4 days incubation at 37°C.

Fig. 2

Transmission electron microscopy of the negatively stained bacteriophage PK16. Scale bar = 100 nm.

Fig. 3

Comparative genomic analysis of phage PK16 and related phages preying on the Bacillus cereus group. Phages that share over 10 best-hit proteins with PK16 were selected and compared using the Easyfig 9 program (Sullivan et al., 2011).