Inhibition of atrazine degradation by cyanazine and exogenous nitrogen in bacterial isolate M91-3

A variety of s-triazine herbicides and nitrogen fertilizers frequently occu r as co-contaminants at pesticide manufacturing and distribution facilities . The degradation of atrazine and cyanazine by the bacterial isolate M91-3 was investigated in washed-cell suspensions and crude cellular extracts. Cy anazine competitively inhibited atrazine degradation. The maximum atrazine degradation rate (V-max) was 41 times higher and the half-saturation consta nt for the inhibitor (K-i) was 1.3 times higher in the crude cellular extra ct than in the washed-cell suspension, suggesting that cellular uptake infl uenced degradation of the s-triazines. Cultures that had received prior exp osure to atrazine and simazine exhibited comparable atrazine degradation ra tes, while cells exposed to cyanazine, propazine, ametryne, cyanuric acid, 2-hydroxyatrazine, biuret, and urea exhibited a lack of atrazine-degradativ e activity. Growth in the presence of exogenous inorganic nitrogen inhibite d subsequent atrazine-degradative activity in washed-cell suspensions, sugg esting that regulation of s-triazine and nitrogen metabolism are linked in this bacterial isolate. These findings have significant implications for th e environmental fate of s-triazines in agricultural settings since these he rbicides are frequently applied to soils receiving N fertilizers. Furthermo re, these results suggest that bioremediation of s-triazine-contaminated si tes (common at pesticide distribution facilities in the cornbelt) may be in hibited by the presence of N fertilizers that occur as co-contaminants.