The potential of soil microorganisms to mineralize atrazine as predicted by MCH-PCR followed by nested PCR

The potential of soil microorganisms to mineralize atrazine was studied in soil samples collected from fields with various histories of atrazine appli cation. In contrast to many previous studies, which showed no atrazine mine ralization activity, all the tested soils mineralized atrazine regardless o f their atrazine application history. However, the delay before mineralizat ion and the variation in the subsequent mineralization rate were in agreeme nt with the initial copy number of the atrazine dechlorinaze gene, and the proliferation rate of the degraders. Soils from corn fields, which had up t o 100 copies of the atzA gene per gram of soil, had a lag period of 4-5 day s before atrazine mineralization started, and final mineralization percenta ges ranged from 40% to 54%. However, soils from fields that were never amen ded with atrazine had much longer lag periods (more than 17 days), which de creased after enrichment of the degrader population with high concentration s of atrazine for 15 days. Generally the mineralization rate and the atzA g ene copy number increased after the enrichment period. The atrazine mineral ization potential was measured by PCR of genes from the atrazine mineraliza tion pathway. Magnetic capture hybridization was the most efficient of the two tested methods for purifying target DNA of PCR inhibitors, without redu cing the copy number of the required fragment. Nested PCR proved to be the most effective method for predicting the exact potential of the soil to min eralize the pollutant even without enrichment of a small population with th e target genes. This method can complement microcosm studies and eliminate futile efforts when the potential to mineralize the pollutant does not exis t in the soil.