Serine and purine synthesis pathways are involved in the virulence of Burkholderia gladioli, the causative agent of gladiolus rot

Burkholderia is a genus of aerobic gram-negative bacteria belonging to the phylum Proteobacteria. B. gladioli causes rot symptoms in economically important crops and expensive ornamental plants, including rice, gladiolus, onion, and cymbidium. B. gladioli and B. glumae produce the toxin toxoflavin, a major virulence factor associated with disease development. However, the pathogenic mechanisms of B. gladioli remain largely unknown. Here, we constructed transposon library of B. gladioli and screened two mutants with reduced virulence among about 800 mutant strains. The position where the transposon was inserted on the genome was in purM and serC in the mutant strains. Inoculation tests were conducted using strains in which each serC and purM were complemented with a plasmid. The area showing symptoms increased significantly compared to that of the mutants, and the amount of toxoflavin produced in the purM mutant strain was significantly reduced. In contrast, toxoflavin production was observed in the purM-complemented strain. These findings indicate that both serC and purM are involved in the virulence of B. gladioli.