Effect of phenylurea herbicides on soil microbial communities estimated byanalysis of 16S rRNA gene fingerprints and community-level physiological profiles

The effect of three phenyl urea herbicides (diuron, linuron, and chlorotolu ron) on soil microbial communities was studied by using soil samples with a 10-year history of treatment. Denaturing gradient gel electrophoresis (DGG E) was used for the analysis of 16S rRNA genes (16S rDNA), The degree of si milarity between the 16S rDNA profiles of the communities was quantified by numerically analysing the DGGE band patterns. Similarity dendrograms showe d that the microbial community structures of the herbicide-treated and nont reated soils were Significantly different, Moreover, the bacterial diversit y seemed to decrease in sops treated with urea herbicides, and sequence det ermination of several DGGE fragments showed that the most affected species in the soils treated with diuron and linuron belonged to an uncultivated ba cterial group, As well as the 16S rDNA fingerprints, the substrate utilizat ion patterns of the microbial communities were compared, Principal-componen t analysis performed on BIOLOG data showed that the functional abilities of the soil microbial communities were, altered by the application of the her bicides. In addition, enrichment cultures of the different soils in medium with the urea herbicides as the sole carbon and nitrogen source showed that there was no difference between treated and nontreated soil in the rate of transformation of diuron and chlorotoluron but that there was a strong dif ference in the case of linuron, In the enrichment cultures with linuron-tre ated soil, linuron disappeared completely after 1 week whereas no significa nt transformation aas observed in cultures inoculated with nontreated soil even after 4 weeks, In conclusion, this study showed that both the structur e and metabolic potential of soil microbial communities were clearly affect ed by a long-term application of urea herbicides.