DERIVATION OF MUTANTS OF ERWINIA-CAROTOVORA SUBSP BETAVASCULORUM DEFICIENT IN EXPORT OF PECTOLYTIC ENZYMES WITH POTENTIAL FOR BIOLOGICAL-CONTROL OF POTATO SOFT-ROT

Erwinia carotovora subsp. betavasculorum Ecb168 produces an antibiotic (s) that suppresses growth of the related bacterium Erwinia carotovora subsp. carotovora in culture and in wounds of potato tubers. Strain E cb168 also produces and secretes pectolytic enzymes and causes a vascu lar necrosis and root rot of sugar beet. Genes (out) involved in secre tion of pectolytic enzymes by Ecb168 were localized to two HindIII fra gments (8.5 and 10.5 kb) of Ecb168 genomic DNA by hybridization to the cloned out region of E. carotovora subsp. carotovora and by complemen tation of Out(-) mutants of E. carotovora subsp. carotovora. Out(-) mu tants of Ecb168, which did not secrete pectate lyase into the culture medium, were obtained when deletions internal to either HindIII fragme nt were introduced into the genome of Ecb168 through marker exchange m utagenesis. Out(-) mutants of Ecb168 were complemented to the Out(+) p henotype by introduction of the corresponding cloned HindIII fragment. Out(-) mutants of Ecb168 were less virulent than the Out(+) parental strain on potato tubers. Strain Ecb168 and Out(-) derivatives inhibite d the growth of E carotovora subsp. carotovora in culture, indicating that the uncharacterized antibiotic(s) responsible for antagonism was exported through an out-independent mechanism. Strain Ecb168 and Out(- ) derivatives reduced the establishment of large populations of E. car otovora subsp. carotovora in wounds of potato tubers and suppressed tu ber soft rot caused by E. carotovora subsp. carofovora.