Characterisation of an Inhibitory Strainof Pseudomonas syringae pv. syringaewith Potential as a Biocontrol Agentfor Bacterial Blight on Soybean

摘要

The soybean epiphyte Pseudomonas syringae pv. syringae 22d/93(Pss22d) exhibits strong potential to control Pseudomonas syringae pv. glycinea(Psg), the causal agent of bacterial blight. Under greenhouse and field conditions theantagonism has been proven, but the underlying mechanisms are unclear, up to now.The secondary metabolites are of particular interest for this antagonism. We focus ourinvestigation on the influence of produced toxins of the biological control system. The antagonist produces the well-known syringomycin, syringopeptin and oneunknown toxin, which inhibits the pathogen in vitro. The unknown toxin wasdetected by an agar diffusion bioassay using Psg as indicator strain. This growthinhibition was reversed by arginine and not by argininosuccinate, suggesting that theunknown toxin could interfere with this step of citrulline/arginine biosynthesis. Via marker exchange mutagenesis in genes coding for nonribosomal proteinsynthesis responsible for initial steps in biosynthesis of syringomycin (syrE) andsyringopeptin (sypA), toxin negative mutants were constructed. Subsequently, adouble mutant in which both genes were deleted was constructed, as well. In plantacoinoculation experiments with the double mutant of Pss22d and the pathogenindicated that syringomycin and syringopeptin did not affect the antagonism.