Mineralization of s-triazine herbicides by a newly isolated Nocardioides species strain DN36

A novel s-triazine-mineralizing bacterium—Nocardioides sp. strain DN36—was isolated from paddy field soil treated with ring-U-¹⁴C-labeled simetryn (¹⁴C]simetryn) in a model paddy ecosystem (microcosm). In a tenfold-diluted R2A medium, strain DN36 liberated ¹⁴CO₂ from not only ¹⁴C]simetryn but also three ring-U-¹⁴C-labeled s-triazines: atrazine, simazine, and propazine. We found that DN36 mineralized ring-U-¹⁴C–cyanuric acid added as an initial substrate, indicating that the bacterium mineralized s-triazine herbicides via a common metabolite, namely, cyanuric acid. Strain DN36 harbored a set of genes encoding previously reported s-triazine-degrading enzymes (TrzN-AtzB-AtzC), and it also transformed ametryn, prometryn, dimethametryn, atraton, simeton, and prometon. The findings suggest that strain DN36 can mineralize a diverse range of s-triazine herbicides. To our knowledge, strain DN36 is the first Nocardioides strain that can individually mineralize s-triazine herbicides via the ring cleavage of cyanuric acid. Further, DN36 could not grow on cyanuric acid, and the degradation seemed to occur cometabolically.