| Abstract | Nitroguanidine (NQ) is an energetic materialthat is used as a key ingredient of triple-base propellants and is currently being considered as a TNT replacement in explosive formulations. NQ was efficiently degraded in aerobic microcosms when a carbon source was added. NQ persisted in unamended microcosms or under anaerobic conditions. An aerobic NQ-degrading bacterium, Variovorax strain VC1, was isolated from soil microcosms containing NQ as the sole nitrogen source. NQ degradation was inhibited in the presence of a more favorable source of nitrogen. Resting cells of VC1 degraded NQ effectively (54 μmol h⁻¹g⁻¹ protein) giving NH₃ (50.0%), nitrous oxide (N₂O) (48.5%) and CO₂ (100%). Disappearance of NQ was accompanied by the formation of a key intermediate product that we identified as nitrourea by comparison with a reference material. Nitrourea is unstable in water and suffered both biotic and abiotic decomposition to eventually give NH₃, N₂O, and CO₂. However, we were unable to detect urea. Based on products distribution and reaction stoichiometry, we suggested that degradation of NQ, O₂NN≕C(NH₂)₂, might involve initial enzymatic hydroxylation of the imine, ⋯C≕N⋯ bond, leading first to the formation of the unstable α-hydroxynitroamine intermediate, O₂NNHC(OH)-(NH₂)₂, whose decomposition in water should lead to the formation of NH₃, N₂O, and CO₂.NQ biodegradation was induced by nitroguanidine itself, L-arginine, and creatinine, all being iminic compounds containing a guanidine group. This first description of NQ mineralization by a bacterial isolate demonstrates the potential for efficient microbial remediation of NQ in soil. |
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