Deciphering unique enzymatic pathways in sulfonamide biotransformation by direct ammonia oxidizer Alcaligenes ammonioxydans HO-1.

Heterotrophic nitrification, similar to autotrophic nitrification, involves key enzymes and reactive nitrogen intermediates during ammonia oxidation, which may influence antibiotic transformation. However, the interference between antibiotic transformation products from ammonia oxidation and secondary metabolites in heterotrophic nitrifiers makes antibiotic transformation pathways more complicated. In this work, we observe that the heterotrophic nitrifier Alcaligenes ammonioxydans HO-1 can effectively convert sulfonamide antibiotics. Product analysis reveals the impacts of carbon and nitrogen concentrations as well as their ratio on the biotransformation of sulfamethazine (SMZ). The dnfABC gene cluster is identified as essential for mediating SMZ conversion. In vitro enzymatic activity reconstruction further confirms that DnfA exhibits N-oxygenase activity and can catalyze the conversion of various aryl-amines into aryl-nitro compounds. The results of this work not only expand our understanding of the functions of heterotrophic nitrifiers, but also provide a theoretical basis for developing efficient biotechnologies for treating antibiotics.