Department of Biochemistry; BioProcess Technology Institute and Center for Biodegradation Research and Informatics; University of Minnesota; St. Paul, Minnesota 55108
Biocatalysis is important in both natural and engineered environments.
The major global reactions in the biospheric cycling of carbon,
nitrogen, and other elements are catalyzed by microorganisms.
The global carbon cycle includes millions of organic compounds
that are made by plants, microorganisms, and organic chemists.
Most of those compounds are transformed by microbial enzymes.
Degradative metabolism is known as catabolism and yields principally
carbon dioxide, methane, or biomass. Microbial catabolic enzymes
are a great resource for biotechnology. They are the building
blocks for engineering novel metabolic pathways and evolving
improved enzymes in the laboratory. Two multicomponent bacterial
oxygenases, cytochrome P450
cam and toluene dioxygenase, catalyze
the dechlorination of polyhalogenated C
2 compounds. Seven genes
encoding those functional enzyme complexes were coexpressed
in a
Pseudomonas and shown to metabolize pentachloroethane to
nonhalogenated organic acids that were metabolized further to
carbon dioxide. In another example, the enzyme catalyzing the
dechlorination of the herbicide atrazine was subjected to iterative
DNA shuffling to produce mutations. By using a plate screening
assay, mutated atrazine chlorohydrolase that catalyzed a more
rapid dechlorination of atrazine was obtained. The mutant genes
were sequences and found to encode up to 11 amino acid changes.
Atrazine chlorohydrolase is currently being used in a model
municipal water treatment system to test the feasibility of
using enzymes for atrazine decontamination. These data suggest
that the natural diversity of bacterial catabolic enzymes provides
the starting point for improved biocatalytic systems that meet
the needs of commercial applications.
