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Applied and Environmental Microbiology, August 2005, p. 4199-4202, Vol. 71, No. 8
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.8.4199-4202.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Metabolism of the Aliphatic Nitramine 4-Nitro-2,4-Diazabutanal by Methylobacterium sp. Strain JS178

Diane Fournier,¹ Sandra Trott,^2, Jalal Hawari,^1* and Jim Spain³

Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2, Canada,¹ U.S. Air Force Research Laboratory, Tyndall Air Force Base, Florida 32403,² Department of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0512³

Received 9 November 2004/ Accepted 23 February 2005

The aliphatic nitramine 4-nitro-2,4-diazabutanal (NDAB; C₂H₅N₃O₃) is a ring cleavage metabolite that accumulates during the aerobic degradation of the energetic compound hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by various Rhodococcus spp. NDAB is also produced during the alkaline hydrolysis of either RDX or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and during the photolysis of RDX. Traces of NDAB were observed in a soil sampled from an ammunition-manufacturing facility contaminated with both HMX and RDX, suggesting natural attenuation. In this study, we report the isolation of a soil bacterium that is able to degrade NDAB under aerobic conditions. The isolate is a pink-pigmented facultative methylotroph affiliated with the genus Methylobacterium. The strain, named Methylobacterium sp. strain JS178, degrades NDAB as a sole nitrogen source, with concomitant growth and formation of 1 molar equivalent of nitrous oxide (N₂O). Comparison of the growth yield of strain JS178 grown on NDAB, nitrite (NO₂^–), or ammonium (NH₄⁺) as a nitrogen source revealed that 1 N equivalent is assimilated from each mole of NDAB, which completes the nitrogen mass balance. In radiotracer experiments, strain JS178 mineralized 1 C of the [¹⁴C]NDAB produced in situ from [¹⁴C]RDX by Rhodococcus sp. strain DN22. Studies on the regulation of NDAB degradation indicated that allantoin, an intermediate in the purine catabolic pathway and a central molecule in the storage and transport of nitrogen in plants, up-regulated the enzyme(s) involved in the degradation of the nitramine. The results reveal the potential for the sequential participation of rhodococci and methylobacteria to effect the complete degradation of RDX.

Present address: Center for Cellular Dynamics, Wright State University, Dayton, OH 45435.

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