s-Triazine ring compounds are common industrial chemicals: pesticides, resin intermediates, dyes, and explosives. The fate of these compounds in the environment is directly correlated with the ability of microbes to metabolize them. Microbes metabolize melamine and the triazine herbicides such as atrazine via enzyme-catalyzed hydrolysis reactions. Hydrolytic removal of substituents on the s-triazine ring is catalyzed by enzymes from the amidohydrolase superfamily and yields cyanuric acid as an intermediate. Cyanuric acid is hydrolytically processed to yield 3 mol each of ammonia and carbon dioxide. In those cases studied, the genes underlying the hydrolytic reactions are localized to large catabolic plasmids. One such plasmid, pADP-1 from Pseudomonas sp. ADP, has been completely sequenced and contains the genes for atrazine catabolism. Insertion sequence elements play a role in constructing different atrazine catabolic plasmids in different bacteria. Atrazine chlorohydrolase has been purified to homogeneity from two sources. Recombinant Escherichia coli strains expressing atrazine chlorohydrolase have been constructed and chemically cross-linked to generate catalytic particles used for atrazine remediation in soil. The method was used for cleaning up a spill of 1,000 pounds of atrazine to attain a level of herbicide acceptable to regulatory agencies.
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Acknowledgements We acknowledge the contributions of many talented coworkers in the research described in this review. This research was supported by grants 98-35107-6368 from the United States Department of Agriculture-NRI/CGP/CSREES, Syngenta Crop Protection, and postdoctoral fellowships from the United States-Israel Binational Agricultural Research and Development (BARD) fund grant number FI-295-99 (to N.S.) and from the NIH Biotechnology Training Grant number GM08347 (to B.M.).