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Applied and Environmental Microbiology, January 2004, p. 508-517, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.508-517.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Biodegradation of Nitro-Substituted Explosives 2,4,6-Trinitrotoluene, Hexahydro-1,3,5-Trinitro-1,3,5-Triazine, and Octahydro-1,3,5,7-Tetranitro-1,3,5-Tetrazocine by a Phytosymbiotic Methylobacterium sp. Associated with Poplar Tissues (Populus deltoides x nigra DN34)

Benoit Van Aken,^* Jong Moon Yoon, and Jerald L. Schnoor

Department of Civil and Environmental Engineering, The University of Iowa, Iowa City, Iowa 52242

Received 2 July 2003/ Accepted 29 September 2003

A pink-pigmented symbiotic bacterium was isolated from hybrid poplar tissues (Populus deltoides x nigra DN34). The bacterium was identified by 16S and 16S-23S intergenic spacer ribosomal DNA analysis as a Methylobacterium sp. (strain BJ001). The isolated bacterium was able to use methanol as the sole source of carbon and energy, which is a specific attribute of the genus Methylobacterium. The bacterium in pure culture was shown to degrade the toxic explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazene (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX). [U-ring-¹⁴C]TNT (25 mg liter^-1) was fully transformed in less than 10 days. Metabolites included the reduction derivatives amino-dinitrotoluenes and diamino-nitrotoluenes. No significant release of ¹⁴CO₂ was recorded from [¹⁴C]TNT. In addition, the isolated methylotroph was shown to transform [U-¹⁴C]RDX (20 mg liter^-1) and [U-¹⁴C]HMX (2.5 mg liter^-1) in less than 40 days. After 55 days of incubation, 58.0% of initial [¹⁴C]RDX and 61.4% of initial [¹⁴C]HMX were mineralized into ¹⁴CO₂. The radioactivity remaining in solution accounted for 12.8 and 12.7% of initial [¹⁴C]RDX and [¹⁴C]HMX, respectively. Metabolites detected from RDX transformation included a mononitroso RDX derivative and a polar compound tentatively identified as methylenedinitramine. Since members of the genus Methylobacterium are distributed in a wide diversity of natural environments and are very often associated with plants, Methylobacterium sp. strain BJ001 may be involved in natural attenuation or in situ biodegradation (including phytoremediation) of explosive-contaminated sites.

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* Corresponding author. Mailing address: Department of Civil and Environmental Engineering, The University of Iowa, 4105 Seamans Center, Iowa City, IA 52242. Phone: (319) 335-5866. Fax: (319) 335-5660. E-mail: bvanaken{at}engineering.uiowa.edu.

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Applied and Environmental Microbiology, January 2004, p. 508-517, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.508-517.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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