Aerobic Mineralization of Nitroguanidine by Variovorax Strain VC1 Isolated from Soil

摘要

Nitroguanidine (NQ) is an energetic material that 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~(-1) g~(-1) protein) giving NH_3 (50.0%), nitrous oxide (N_2O) (48.5%) and CO_2 (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 NHV N,O, and CO,. However, we were unable to detect urea. Based on products distribution and reaction stoichiometry, we suggested that degradation of NQ, O_2NN=C(NH_2)_2, might involve initial enzymatic hydroxylation of the mine, -C=N- bond, leading first to the formation of the unstable a-hydroxynitroamine intermediate, O_2NNHC(OH)-(NH_2)_2, whose decomposition in water should lead to the formation of NH_3, N_2O, and CO_2. 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.