Microbial degradation of explosives: biotransformation versus mineralization |
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Authors: | J Hawari S Beaudet A Halasz S Thiboutot G Ampleman |
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Institution: | (1) Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Ave, Montréal, Québec H4P 2R2, Canada e-mail: jalal.hawari@nrc.ca Fax: +1-514-4966265, CA;(2) Defence Research Establishment Valcartier, Department of National Defence, Val Belair, Québec G3J 1X5, Canada, CA |
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Abstract: | The nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) is a reactive molecule that biotransforms readily under both aerobic
and anaerobic conditions to give aminodinitrotoluenes. The resulting amines biotransform to give several other products, including
azo, azoxy, acetyl and phenolic derivatives, leaving the aromatic ring intact. Although some Meisenheimer complexes, initiated
by hydride ion attack on the ring, can be formed during TNT biodegradation, little or no mineralization is encountered during
bacterial treatment. Also, although the ligninolytic physiological phase and manganese peroxidase system of fungi can cause
some TNT mineralization in liquid cultures, little to no mineralization is observed in soil. Therefore, despite more than
two decades of intensive research to biodegrade TNT, no biomineralization-based technologies have been successful to date.
The non-aromatic cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine
(HMX) lack the electronic stability enjoyed by TNT or its transformed products. Predictably, a successful enzymatic change
on one of the N–NO2 or C–H bonds of the cyclic nitramine would lead to a ring cleavage because the inner C–N bonds in RDX become very weak (<2 kcal/mol).
Recently this hypothesis was tested and proved feasible, when RDX produced high amounts of carbon dioxide and nitrous oxide
following its treatment with either municipal anaerobic sludge or the fungus Phanaerocheate chrysosporium. Research aimed at the discovery of new microorganisms and enzymes capable of mineralizing energetic chemicals and/or enhancing
irreversible binding (immobilization) of their products to soil is presently receiving considerable attention from the scientific
community.
Received: 14 February 2000 / Received revision: 9 June 2000 / Accepted: 13 June 2000 |
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