Oxidation of aminonitrotoluenes by 2,4-DNT dioxygenase of Burkholderia sp. strain DNT.

Aminonitrotoluenes form rapidly from the reduction of dinitrotoluenes (DNTs) which are priority pollutants and animal carcinogens. For example, 4-amino-2-nitrotoluene (4A2NT) and 2A4NT accumulate from the reduction of 2,4-DNT during its aerobic biodegradation. Here, we show that 2,4-DNT dioxygenase (DDO) from Burkholderia sp. strain DNT oxidizes the aminonitrotoluenes 2A3NT, 2A6NT, 4A3NT, and 5A2NT to 2-amino-3-nitrobenzylalcohol, 2-amino-4-nitro-m-cresol and 3-amino-5-nitro-p-cresol, 4-amino-3-nitrobenzylalcohol and aminonitrocresol, and 2-amino-5-nitro-o-cresol, respectively. 2A5NT and 3A4NT are oxidized to aminonitrocresols and/or aminonitrobenzylalcohols, and 4A2NT is oxidized to aminonitrocresol. Only 2A4NT, a reduced compound derived from 2,4-DNT, was not oxidized by DDO or its three variants. The alpha subunit mutation I204Y resulted in two to fourfold faster oxidization of the aminonitrotoluenes. Though these enzymes are dioxygenases, they acted like monooxygenases by adding a single hydroxyl group, which did not result in the release of nitrite.