Effect of cyanuric acid amendment on atrazine mineralization in surface soils and detection of the s-triazine ring-cleavage gene trzD

Cyanuric acid amendment was tested for potential enhancement of atrazine mineralization activity because this compound is the metabolite in the degradation pathway of s-triazines prior to ring-cleavage. The effect of cyanuric acid on: (i) subsequent atrazine mineralization kinetics and (ii) the detection of a hybridization signal to the s-triazine ring-cleavage gene trzD in surface soils with different histories of atrazine application were examined in this study. Composite soil samples from two agricultural soils and one riparian zone soil were amended with cyanuric acid. Mineralization was measured as 14CO2 evolution in samples spiked with [14C-U-ring]-labeled atrazine. Dot-blot hybridization assays were performed on total genomic DNA extracted from the soils using the gene trzD (cyanuric acid amidohydrolase) as a probe. The source of this gene is Pseudomonas NRRLB-12228, which can cleave the s-triazine ring, but cannot grow with atrazine. The cyanuric acid amendment had a variable effect on the subsequent mineralization of atrazine in all three soils. The trzD hybridization signals in all three soils were negligible or undetectable, although parallel mineralization studies of one of the agricultural soils showed fast and extensive 14CO2 evolution from [ring-U-14C]-atrazine. The results suggest that the trzD gene, which is currently the only known s-triazine ring-cleavage gene, is not dominant among the atrazine-degrading populations of these soils.