Determination of Key Metabolites during Biodegradation of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine with Rhodococcus sp. Strain DN22
AIR FORCE RESEARCH LAB TYNDALL AFB FL
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Rhodococcus sp. strain DN22 can convert hexahydro-1,3,5-triazine RDX to nitrite, but information on degradation products or the fate of carbon is not known. The present study describes aerobic biodegradation of RDX 175 microns when used as an N source for strain DN22. RDX was converted to nitrite NO2 30, nitrous oxide N2O 3.2, ammonia 10, and formaldehyde HCHO 27, which later converted to carbon dioxide. In experiments with ring-labeled 15N-RDX, gas chromatographicmass spectrophotometric GCMS analysis revealed N2O with two molecular mas ions one at 44 Da, corresponding to 14N14NO, and the second at 45 Da, corresponding to 15N14NO. The nonlabeled N2O could be formed only from -NO2, whereas the 15N-labeled one was presumed to originate from a nitramine group 15N-14NO2 in RDX. Liquid chromatographic LC-MS electrospray analyses indicated the formation of a dead end product with a deprotonated molecular mass ion M-H at 118 Da. High-resolution MS indicated a molecular formula of C2H5N3O3. When the experiment was repeated with ring-labeled 15N-RDX, the M-H appeared at 120 Da, indicating the two of the three N atoms in the metabolite originated from the ring in RDX. When U-14C-RDX was used in the experiment, 64 of the original radioactivity in RDX incorporated into the metabolite with a molecular weight MW of 119 high-pressure LCradioactivity and 30 in 14CO2 minearlization after 4 days of incubation, suggesting that one of the carbon atoms in RDX was converted to CO2 and the other two were incorporated in the ring cleavage product with an MW of 119. Based on the above stoichiometry, we propose a degradation pathway for RDX based on initial denitration followed by ring cleavage to formaldehyde and the dead end product with an MW of 119.
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