Biodegradation of the Nitramine Explosive CL-20

Abstract

The cyclic nitramine explosive CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) was examined in soil microcosms to determine whether it is biodegradable. CL-20 was incubated with a variety of soils. The explosive disappeared in all microcosms except the controls in which microbial activity had been inhibited. CL-20 was degraded most rapidly in garden soil. After 2 days of incubation, about 80% of the initial CL-20 had disappeared. A CL-20-degrading bacterial strain, Agrobacterium sp. strain JS71, was isolated from enrichment cultures containing garden soil as an inoculum, succinate as a carbon source, and CL-20 as a nitrogen source. Growth experiments revealed that strain JS71 used 3 mol of nitrogen per mol of CL-20. 4,6,8,10,4,6,8,10,) is a new, highly energetic explosive related to the explosives RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) (Fig. 1). Due to its higher energy and its moderate sensitivity, CL-20 is expected to replace earlier explosives (19,20,22,25). The production of CL-20 and its use in munitions and propellants can be expected to lead to environmental contamination. RDX and HMX, common contaminants in soil and groundwater at munition manufacturing sites and firing ranges, are toxic and possibly carcinogenic (7,8,11,12,16,23,27). Because of the structural similarity of CL-20 to RDX and HMX, it is likely that CL-20 has similar effects. So far, there is little information available about the properties of CL-20. In contrast to RDX and HMX, CL-20 is a caged molecule (Fig. 1). The water solubility of CL-20 is 4.8 mg/liter at 25°C (Stevens Institute of Technology [http://www.cee.stevens-tech.edu/ResProj.html]), which is lower than the solubility of the nitramines RDX and HMX (38.4 and 6.6 mg/liter at 20°C, respectively) (27).The microbial degradation of RDX and HMX under aerobic and anaerobic conditions has been extensively investigated (1, 2, 4-6, 9, 13-15, 17, 21). Under anaerobic conditions, three degradation pathways have been proposed. The first includes the production of nitroso derivatives of RDX and HMX, which are subject to further degradation (15, 21). Hawari et al. suggested a second degradation pathway which includes the direct ring cleavage of RDX and HMX without the initial reduction of the nitro groups (14, 15). The third proposed degradation pathway is based on N denitration prior to ring cleavage (1).Under aerobic conditions, RDX is degraded by a yet-unknown mechanism. The initial attack seems to be catalyzed by a cytochrome P450 (1a, 6, 24). RDX degradation by Rhodococcus sp. strain DN22 leads to the formation of nitrite, nitrous oxide, ammonia, formaldehyde, and a dead-end product with a molecular weight of 119 which was recently identified as 4-nitro-2,4-diazabutanal (1a, 5, 9). Fournier et al. proposed a degradation pathway which includes an initial denitration of RDX followed by ring cleavage to formaldehyde and the dead-end product (9).To the best of our knowledge, no biodegradation of CL-20 has...

Initial Reaction(s) in Biotransformation of CL-20 Is Catalyzed by Salicylate 1-Monooxygenase from Pseudomonas sp. Strain ATCC 29352

“…strain FA1 degraded CL-20 and assimilated about 4 mol of nitrogen per mol of CL-20 (4). However, the two previous studies (4,31) detected no initial metabolite(s) and did not describe the involvement of any specific enzyme(s). The present study thus advances our understanding of the initial steps involved in biotransformation of CL-20 by flavoenzyme(s)-producing bacteria.…”

“…For instance, Agrobacterium sp. strain JS71, a soil isolate, degraded CL-20 and assimilated 3 mol of nitrogen per mol of CL-20 (31). In a recent study, Pseudomonas sp.…”

Crystallization and preliminary analysis of active nitroalkane oxidase in three crystal forms

“…Despite their toxic characteristics, recent studies have established that many nitrochemicals are catabolized by prokaryotic and eukaryotic organisms as sources of nitrogen and/or carbon (Somerville et al, 1995;Spain, 1995;French et al, 1998;Hawari et al, 2000;Spain et al, 2000;Ebert et al, 2001;Rosser et al, 2001;Johnson et al, 2002;Seth-Smith et al, 2002;Trott et al, 2003). Indeed, several prokaryotic FMN-dependent enzymes have received recent attention because they reductively eliminate nitrite from xenobiotic explosive compounds, which can serve as a sole source of nitrogen (Spain, 1995;Binks et al, 1996;Blehert et al, 1997Blehert et al, , 1999French et al, 1998;Nivinskas et al, 2000;Riefler & Smets, 2000;Williams & Bruce, 2000;Barna et al, 2001;Ebert et al, 2001;Meah et al, 2001;Haynes et al, 2002;Johnson et al, 2002;Khan et al, 2002;Koder et al, 2002;Williams & Bruce, 2002;Orville, Manning, Blehert, Studts et al, 2004).…”

Fate of CL-20 in sandy soils: Degradation products as potential markers of natural attenuation

“…CL-20 was reported to biodegrade in soil under aerobic (Trott et al, 2003;Crocker et al, 2005;Panikov et al, 2007) and anaerobic (Strigul et al, 2006;Panikov et al, 2007) conditions. Several strains capable of degrading CL-20, including Agrobacterium sp.…”

“…Several strains capable of degrading CL-20, including Agrobacterium sp. strain JS71 (Trott et al, 2003), Pseudomonas sp. strain FA1 (Bhushan et al, 2003), and Clostridium sp.…”