CLONING OF GENES INVOLVED IN THE SYNTHESIS OF PYRROLNITRIN FROM PSEUDOMONAS-FLUORESCENS AND ROLE OF PYRROLNITRIN SYNTHESIS IN BIOLOGICAL-CONTROL OF PLANT-DISEASE

A soil isolate of Pseudomonas fluorescens (BL915) was shown to be an e ffective antagonist of Rhizoctonia solani-induced damping-off of cotto n. Investigation of the biological basis of this antagonism revealed t hat the strain produces pyrrolnitrin, a secondary metabolite known to inhibit R. solani and other fungi. Mutants of strain BL915 that did no t produce pyrrolnitrin and did not suppress damping-off of cotton by R . solani were generated by exposure to N-methyl-N'-nitro-N-nitrosoguan idine. A gene region that was capable of restoring pyrrolnitrin produc tion to the non-pyrrolnitrin-producing mutants and of conferring this ability upon two other P. fluorescens strains not otherwise known to p roduce this compound or to be capable of suppressing damping-off cause d by R. solani was isolated from strain BL915. The non-pyrrolnitrin-pr oducing strains (mutants of BL915 and the other two P. fluorescens str ains) which synthesized pyrrolnitrin after the introduction of the gen e region from strain BL915 were also shown to be equal to strain BL915 in their ability to suppress R. solani-induced damping-off of cotton. These results indicate that we have isolated from P. fluorescens BL91 5 a gene(s) that has a role in the synthesis of pyrrolnitrin and that the production of this compound has a role in the ability of this stra in to control damping-off of cotton by R. solani.