Field-scale remediation of atrazine-contaminated soil using recombinant Escherichia coli expressing atrazine chlorohydrolase

We performed the first field-scale atrazine remediation study in the United States using chemically killed, recombinant organisms. This field study co mpared biostimulation methods for enhancing atrazine degradation with a nov el bioaugmentation protocol using a killed and stabilized whole-cell suspen sion of recombinant Escherichia coli engineered to overproduce atrazine chl orohyrolase, AtzA. AtzA dechlorinates atrazine, producing non-toxic and non -phytotoxic hydroxyatrazine. Soil contaminated by an accidental spill of at razine (up to 29 000 p.p.m.) supported significant populations of indigenou s microorganisms capable of atrazine catabolism. Laboratory experiments ind icated that supplementing soil with carbon inhibited atrazine biodegradatio n, but inorganic phosphate stimulated atrazine biodegradation. A subsequent field-scale study consisting of nine (0.75 m(3)) treatment plots was desig ned to test four treatment protocols in triplicate. Control plots contained moistened soil; biostimulation plots received 300 p.p.m. phosphate; bioaug mentation plots received 0.5% (w/w) killed, recombinant E. coli cells encap sulating AtzA; and combination plots received phosphate plus the enzyme-con taining cells. After 8 weeks, atrazine levels declined 52% in plots contain ing killed recombinant E. coli cells, and 77% in combination plots. In cont rast, atrazine levels in control and biostimulation plots did not decline s ignificantly. These data indicate that genetically engineered bacteria over expressing catabolic genes significantly increased degradation in this soil heavily contaminated with atrazine.