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

Abstract

We performed the first field-scale atrazine remediation study in the United States using chemically killed, recombinant organisms. This field study compared biostimulation methods for enhancing atrazine degradation with a novel bioaugmentation protocol using a killed and stabilized whole-cell suspension of recombinant Escherichia coli engineered to overproduce atrazine chlorohyrolase, AtzA. AtzA dechlorinates atrazine, producing non-toxic and non-phytotoxic hydroxyatrazine. Soil contaminated by an accidental spill of atrazine (up to 29,000 p.p.m.) supported significant populations of indigenous microorganisms capable of atrazine catabolism. Laboratory experiments indicated that supplementing soil with carbon inhibited atrazine biodegradation, but inorganic phosphate stimulated atrazine biodegradation. A subsequent field-scale study consisting of nine (0.75m3) treatment plots was designed to test four treatment protocols in triplicate. Control plots contained moistened soil; biostimulation plots received 300p.p.m. phosphate; bioaugmentation plots received 0.5% (w/w) killed, recombinant E. coli cells encapsulating AtzA; and combination plots received phosphate plus the enzyme-containing cells. After 8 weeks, atrazine levels declined 52% in plots containing killed recombinant E. coli cells, and 77% in combination plots. In contrast, atrazine levels in control and biostimulation plots did not decline significantly. These data indicate that genetically engineered bacteria overexpressing catabolic genes significantly increased degradation in this soil heavily contaminated with atrazine.

Biostimulation for the Enhanced Degradation of Herbicides in Soil

“…Lima et al [88] successfully transferred a previously examined "small-scale biostimulation strategy" of atrazine to a larger open soil conditions spiked with commercial formulation at doses, mimicking overuse or concentration "hot spots" that may arise from the uneven application and spill scenarios. In another field evaluation experiment, Strong et al [89] assessed a range of biostimulation supplements to optimize the nutritional additives and applied this information to the field to test systematically the ability of different bioremediation methods to remediate soil heavily contaminated with atrazine by an accidental spill.…”

New aspects on atrazine biodegradation

“…In a field-scale remediation study of a soil contaminated by an accidental spill of atrazine (up to 29,000 ppm), bioaugmentation was performed using a killed and stabilized whole-cell suspension of recombinant E. coli engineered to overproduce atrazine chlorohydrolase, AtzA. After eight weeks, atrazine levels declined by 52% in plots containing killed recombinant E. coli cells, whereas 77% biostimulation was detected in plots that received 300 ppm of phosphate (Strong et al, 2000). Cell-free crude extracts from Pseudomonas sp.…”

Evolution of Catabolic Pathways: Genomic Insights into Microbial s -Triazine Metabolism

“…A. aurescens TC1 is exceptional, utilizing various s-triazines as both sole carbon and nitrogen sources. A. aurescens TC1 was isolated at a roadside spill site, where 1,000 pounds of atrazine had contaminated 35 cubic yards of soil; the site was bioremediated to acceptable levels with approval by the U.S. Environmental Protection Agency (71,72). The method of treatment in that study was a recombinant Escherichia coli strain containing highly expressed AtzA.…”