Isolation and characterization of a 4-nitrotoluene-oxidizing enzyme from activated sludge by a metagenomic approach

To isolate a biocatalytic enzyme, metagenomic libraries were constructed in fosmids from samples of activated sludge used to treat coke plant wastewater. Six indigo-producing clones were isolated from approximately 40,000 metagenomic clones in the search for the oxygenase responsible. In vitro mutagenesis and whole-sequencing revealed one open reading frame to be responsible for the production of indigo in the fosmid clones. The deduced sequence of the gene product showed 60% identity with 2-naphthoate monooxygenase from Burkholderia sp. JT1500. Subclones carrying this open reading frame (icpA) retained indigo production, and indigo-producing enzymes expressed from subclones catalyzed the oxidization of 4-nitrotoluene to form 4-nitrobenzyl alcohol. These results suggested that the icp product is an enzyme involved in catalyzing 4-nitrotoluene's oxygenation.