A genetically engineered microorganism, Pseudomonas putida PP0301 (pR0103), and the plasmidless parent strain, PP0301, were added at approximately ten to the seventh CFU/g of soil amended with 500 ppm of 2,4-dichlorophenoxyacete (2,4-D) (500 microgram/g). The degradation of 2,4-D and the accumulation of a single metabolite, identified by gas chromatography-mass spectrophotometry as 2,4-dichlorophenol (2,4-DCP), occurred only in soil inoculated with PP0301 (pR0103), wherein 2,4-DCP accumulated to >70 ppm for 5 weeks and the concentration of 2,4-D was reduced to <100 ppm. Coincident with the accumulation of 2,4-DCP was a >400-fold decline in the numbers of fungal propagules and a marked reduction in the rate of CO2 evolution, whereas 2,4-D did not depress either fungal propagules or respiration of the soil microbiota. 2,4-DCP did not appear to depress the numbers of total heterotrophic, sporeforming, or chitin-utilizing bacteria. (Copyright (c) 1991, American Society for Microbiology.)