38
s-triazine herbicides (Topp et al. 2000). P-2 and P-3 are oxidative-hydrolytic pathways involving initial oxidative N-dealkylation of atrazine to deethylatrazine or
deisopropylatrazine respectively by nonspecific monooxygenases (Devers et al.
2004). These products are dealkylated again to deisopropyldeethylatrazine, which is
converted to cyanuric acid by hydrolytic dechlorination, deamination, and/or dealkylation (Govantes et al. 2009). Atrazine degradation via these routes is mostly
reported by a consortium rather than individual bacteria and is less common. In the
second stage, hydrolytic cleavage of the s-triazine ring of cyanuric acid and subsequently hydrolysis of biuret and allophanate occur to yield ammonia and carbon
dioxide (Fig. 2.3). In most of the atrazine mineralising bacteria, these enzymes are
encoded by the atzDEF operon (Fruchey et al. 2003; Karns 1999; Shapir et al.
2005b). Homologues to AtzD (TrzD) and AtzF (TrzF) perform the equivalent reactions in other bacteria with small differences in substrate affinity and specificity
(Rousseaux et al. 2001; Shapir et al. 2006). Atrazine will be biodegraded to cyanuric
acid by one of the above three pathways.
Rhodococcus sp. strain FJ1117YT degrades the methylthio-s-triazines such as
simetryn, ametryn, desmetryn, dimethametryn, and prometryn when supplied as the
sole sulphur source. The biodegradation pathway of simetryn involves the formation of methylsulfinyl analogue as the first metabolite followed by methylsulfonyl
Fig. 2.2 Atrazine degradative pathways (P1, P2, and P3) showing conversion of atrazine to cyanuric acid
K. Rajendran et al.
s-triazine herbicides (Topp et al. 2000). P-2 and P-3 are oxidative-hydrolytic pathways involving initial oxidative N-dealkylation of atrazine to deethylatrazine or
deisopropylatrazine respectively by nonspecific monooxygenases (Devers et al.
2004). These products are dealkylated again to deisopropyldeethylatrazine, which is
converted to cyanuric acid by hydrolytic dechlorination, deamination, and/or dealkylation (Govantes et al. 2009). Atrazine degradation via these routes is mostly
reported by a consortium rather than individual bacteria and is less common. In the
second stage, hydrolytic cleavage of the s-triazine ring of cyanuric acid and subsequently hydrolysis of biuret and allophanate occur to yield ammonia and carbon
dioxide (Fig. 2.3). In most of the atrazine mineralising bacteria, these enzymes are
encoded by the atzDEF operon (Fruchey et al. 2003; Karns 1999; Shapir et al.
2005b). Homologues to AtzD (TrzD) and AtzF (TrzF) perform the equivalent reactions in other bacteria with small differences in substrate affinity and specificity
(Rousseaux et al. 2001; Shapir et al. 2006). Atrazine will be biodegraded to cyanuric
acid by one of the above three pathways.
Rhodococcus sp. strain FJ1117YT degrades the methylthio-s-triazines such as
simetryn, ametryn, desmetryn, dimethametryn, and prometryn when supplied as the
sole sulphur source. The biodegradation pathway of simetryn involves the formation of methylsulfinyl analogue as the first metabolite followed by methylsulfonyl
Fig. 2.2 Atrazine degradative pathways (P1, P2, and P3) showing conversion of atrazine to cyanuric acid
K. Rajendran et al.