Isolation of Burkholderia jumbo phages and their utilization as biocontrol agents to suppress rice seedling rot disease

Jumbo bacteriophages, which have genomic DNA larger than 200 k-bp, are attracting attention as potential biocontrol agents to suppress bacterial diseases in cultivated crops because they generally have a broader host range of phytopathogenic bacteria compared with ordinary bacteriophages. Thus, the identification of new jumbo phages from environmental and agricultural resources is required to develop effective biological control materials. In a survey of phages targeting the phytopathogenic bacterium Burkholderia glumae, bacteriophages FLC8, FLC9, and FLC10 were isolated from fallen leaf compost. All three phages had an icosahedral head and tail structure. FLC8 and FLC9 had 225,545-bp and 321,833-bp genomic DNA, respectively, indicating that they could be classified as jumbo phages, whereas FLC10 had 32,867-bp genomic DNA, indicating that it was an ordinary phage. All three phages clearly suppressed rice seedling rot disease caused by B. glumae: the control values were 77.1 of FLC8, 82.1 of FLC9 and 33.3 of FLC10, respectively. FLC8 and FLC9 could infect five B. glumae and six B. plantarii strains, which were all strains using analysis of phage host range, while FLC10 had a narrow host range. Evaluation of the preservation condition of both jumbo phages revealed that ~ 90% infectivity of them was maintained in phage buffer (pH 7.5) at 4 °C for ~ 30 days.