Enzymatic degradation of chlorodiamino-s-triazine

Abstract

2-Chloro-4,6-diamino-s-triazine (CAAT) is a metabolite of atrazine biodegradation in soils. Atrazine chlorohydrolase (AtzA) catalyzes the dechlorination of atrazine but is unreactive with CAAT. In this study, melamine deaminase (TriA), which is 98% identical to AtzA, catalyzed deamination of CAAT to produce 2-chloro-4-amino-6-hydroxy-s-triazine (CAOT). CAOT underwent dechlorination via hydroxyatrazine ethylaminohydrolase (AtzB) to yield ammelide. This represents a newly discovered dechlorination reaction for AtzB. Ammelide was subsequently hydrolyzed by N-isopropylammelide isopropylaminohydrolase to produce cyanuric acid, a compound metabolized by a variety of soil bacteria.

FIG. 1.

Chemical structures of atrazine (A) and melamine (B).

FIG. 2.

Growth of recombinant E. coli on several potential nitrogen sources. Shown are results for E. coli(pJS5) (A) with CAAT as the sole nitrogen source, E. coli DH5α (B) with CAAT as the sole nitrogen source, E. coli(pATZB) (C) with CAOT as the sole nitrogen source, and E. coli(pATZC) (D) with ammelide as the sole nitrogen source (n = 3). Standard error bars are shown by vertical lines at each time point.

FIG. 3.

Proposed hypothetical pathway for the degradation of CAAT.