MOLECULAR-GENETIC ANALYSIS OF THE RESPONSE OF 3 SOIL MICROBIAL COMMUNITIES TO THE APPLICATION OF 2,4-D

The responses of three different soil microbial communities to the exp erimental application of 2,4-dichlorophenoxyacetic acid (2,4-D) were e valuated with a variety of molecular genetic techniques. Two of the th ree soil communities had histories of prior direct exposure to 2,4-D, and one had no prior direct application of any herbicide. Dominant 2,4 -D degrading strains isolated from these soils the previous year were screened for hybridization with three catabolic genes (tfdA, tfdAII, a nd tfdB) cloned from the well-studied 2,4-D degradative plasmid, pJP4, revealing varying degrees of similarity with the three genes. Hybridi zation of total community DNA from the three soils with the tfd gene p robes also indicated that pJP4-like tfd genes were not harboured by a significant percentage of the community. Community level response was evaluated by the comparison of different treatments by Random Amplifie d Polymorphic DNA (RAPD) fingerprints and by community DNA cross-hybri dization. No differences between treatments within the same soil were detected in any of the RAPD fingerprints generated with 17 primers. Co mmunity DNA cross-hybridization also indicated that the application of 2,4-D at the applied rates did not quantitatively affect the structur e of the soil microbial communities present in the three soils during the time-frame studied.