Molecular approaches to investigate herbicide-induced bacterial community changes in soil microcosms

Since biochemical and microbiological methods used to study microbial commu nity changes induced by anthropogenic activities can be biased, the impact of two herbicides on soil microorganisms was investigated by culture-indepe ndent molecular techniques. The effect of three different amounts (the reco mmended field dose. tenfold, and 100-fold the dose) of propanil or prometry ne on the bacterial community of a clay soil, two modalities of incubation (soil moisture at 70% of the field capacity and a soil-herbicide suspension , 1:10, w:v). and time of incubation were investigated by denaturing gradie nt gel electrophoresis (DGGE) and amplified rDNA restriction analysis (ARDR A). Two sets of primers for 16S rDNA were used to amplify total soil DNA. S terile and non-sterile samples were used to determine, by HPLC, the amounts of herbicides adsorbed on soil and transformed by soil microorganisms. Pro metryne persisted in soil longer than propanil. Propanil was removed signif icantly more by non-sterile than by sterile samples, while for prometryne, slight differences were observed. 3.4-Dichloroaniline. a product of propani l hydrolysis. was detected in non-sterile samples and increased with incuba tion time. Propanil did not affect soil bacteria significantly as indicated by DGGE and ARDRA. with the only exception being the soil-herbicide suspen sion. Despite a lower utilization of prometryne by soil microorganisms, DGG E analysis showed a more diverse banding than with propanil. Some bands wer e also detected in the DNA sample extracted from the soil-prometryne suspen sion, and could be representative of bacterial species utilizing the herbic ide as a carbon source, in two very different soil microcosms.