ENHANCED GROWTH AND ACTIVITY OF A BIOCONTROL BACTERIUM GENETICALLY-ENGINEERED TO UTILIZE SALICYLATE

Plasmid NAH7 was transferred from Pseudomonas putida PpG7 to P. putida R20 [R20(NAH7)], an antagonist of Pythium ultimum. The plasmid did no t affect growth or survival of R20(NAH7) and was stably maintained und er nonselective conditions in broth and soil and on sugar beet seeds. Plasmid NAH7 conferred to R20(NAH7) the ability to utilize salicylate in culture, agricultural field soil, and on sugar beet seeds. The meta bolic activity of R20(NAH7), but not the wild-type R20, was greatly in creased in soil by amendment with salicylate (250 mug/g) as measured b y induced respiration. Population densities of R20(NAH7) were also enh anced in salicylate-amended soil, increasing from approximately 1 x 10 (5) CFU/g to approximately 3 x 10(8) CFU/g after 35 h of incubation. I n contrast, population densities of R20(NAH7) in nonamended soil were approximately 3 x 10(6) CFU/g of soil after 35 h of incubation. The co ncentration of salicylate in soil affected the rate and extent of popu lation increase by R20(NAH7). At 50 to 250 mug of salicylate per g of soil, population densities of R20(NAH7) increased to approximately 10( 8) CFU/g of soil by 48 h of incubation, with the fastest increase at 1 00 mug/g. A lag phase of approximately 24 h occurred before the popula tion density increased in the presence of salicylate at 500 mug/g; at 1,000 mug/g, population densities of R20(NAH7) declined over the time period of the experiment. Population densities of R20(NAH7) on sugar b eet seeds in soils amended with 100 mug of salicylate per g were not i ncreased while ample carbon was present in the sperinosphere. However, after carbon from the seed had been utilized, population densities of R20(NAH7) decreased significantly less (P = 0.005) on sugar beet seed s in soil amended with salicylate than in nonamended soil.