Analysis of traits for biocontrol performance of Pseudomonas parafulva JBCS1880 against bacterial pustule in soybean plants

Many biocontrol mechanisms including antimicrobial activity have been identified for control of plant diseases. However, the influence of various traits on the biocontrol performance of a specific biological control agent (BCA) remains to be revealed. In this study, to dissect the contribution of various traits to the biocontrol performance of a bacterial BCA, we performed genetic screening using a random transposon (Tn) mutant collection constructed from Pseudomonas parafulva JBCS1880 that shows strong antagonism against Xanthomonas axonopodis pv. glycines and Burkholderia glumae. Suppression of antibacterial activity by Tn insertion reduced the biocontrol performance of the strain. The disruption of viscosin-like lipopeptide, which is predicted to have D-Ser at the second position (called VILS2 hereafter), significantly suppressed not only antagonism, but also swarming motility and biofilm formation of P. parafulva JBCS1880. In addition, surface colonization with swarming motility and siderophore production also contributed to the biocontrol ability of the strain. The results indicate that the coordinated action of VILS2-mediated antibacterial activity and surface movement is critical for biocontrol activity of P. parafulva JBCS1880. Overall, our results suggest that antagonism, swarming motility, and siderophore production are important traits for the biocontrol performance of P. parafulva JBCS1880. This is the first report of the biocontrol of soybean bacterial pustules using a strain of P. parafulva, which is expected to produce a novel lipopeptide. The traits essential for biocontrol performance of the potential BCA were determined, but the functional roles of many genes in biocontrol remain a focus for further investigation.