Microbial metabolism of the s-triazine herbicide ametryn: A comparison to atrazine metabolism

Atrazine and ametryn belong to the s-triazine class of herbicides. Atrazine is one of the most predominant herbicides used in the US today, and its potential risks to the natural, and human, environment continue to be studied. It has recently been linked to a global decline in frog populations. Frogs have been reported to be demasculinized or become hermaphrodites after exposure to low ecologically relevant levels. The microbial degradation of atrazine has been studied in detail in several bacterial strains. The first step in the degradation of atrazine is a hydrolytic dechlorination catalyzed by an atrazine chlorohydrolase (AtzA) to form hydroxyatrazine. Here, I study the degradation of another s-triazine herbicide, ametryn, and how it relates to the degradation of atrazine. Ametryn has a methylthio substituent instead of the chloride substituent of atrazine. The substrate range of the AtzA enzyme is very narrow and AtzA is not capable of removing the methylthio group of ametryn. Consortia capable of metabolizing both atrazine and ametryn were isolated from soil by enrichment and were shown by PCR to contain genes homologous to atzA and trzN . The TrzN enzyme has been linked to the degradation of ametryn in Norcardioides sp. strain C 190. A single bacteria, Arthrobacter aurescens strain TC1, capable of metabolizing both ametryn and atrazine was isolated and characterized in detail. Arthrobacter aurescens strain TC1 was shown to metabolize 35 different s-triazines and to contain the trzN gene. The gene was cloned by PCR, expressed with a his tag in Escherichia coli, purified to homogeneity and shown to be a member of the amidohydrolase superfamily and dependent on metal for catalysis. TrzN was shown to metabolize seven of the 35 s-triazines, including atrazine and ametryn.