Mineralization of the Cyclic Nitramine Explosive Hexahydro-1,3,5-Trinitro-1,3,5-Triazine by Gordonia and Williamsia spp

Abstract

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a cyclic nitroamine explosive that is a major component in many military high-explosive formulations. In this study, two aerobic bacteria that are capable of using RDX as the sole source of carbon and nitrogen to support their growth were isolated from surface soil. These bacterial strains were identified by their fatty acid profiles and 16S ribosomal gene sequences as Williamsia sp. KTR4 and Gordonia sp. KTR9. The physiology of each strain was characterized with respect to the rates of RDX degradation and [U- Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a cyclic nitroamine that is one of the most powerful and commonly used military explosives. RDX has contaminated soils and groundwater at army ammunition plants and other military sites through its manufacture, use on testing and firing ranges, and disposal (22). RDX is a toxic compound that affects the central nervous system of laboratory animals, causing convulsions (10, 37), and it has been proposed as a possible human carcinogen (38). Information on the environmental factors that determine the transport and fate of RDX in soils is needed to accurately assess the risk posed by RDX and to ensure the sustainability of live-fire training exercises.Anaerobic biodegradation of RDX has been extensively studied (1,6,21,23,25,26,29,(42)(43)(44)(45). McCormick et al. (29) proposed a pathway where RDX undergoes sequential reduction of the nitro groups to form hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine; hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine; and hexahydro-1,3,5-trinitroso-1,3,5-triazine. According to the proposed pathway, this transformation then produces formaldehyde, methanol, hydrazine, and dimethyl hydrazine. Hawari et al. (23) proposed another pathway where ring cleavage occurs before sequential reduction, producing the metabolites methylenedinitramine and bis(hydroxymethyl)nitramine.Although most of the initial strains isolated could only degrade RDX anaerobically (25,32,41,42), several pure strains have subsequently been isolated that aerobically degrade RDX as a nitrogen source. Binks et al. (8) isolated Stenotrophomonas maltophilia PB1 and tentatively identified an RDX metabolite as methylene-N-(hydroxymethyl)-hydroxylamine-NЈ-(hydroxymethyl)nitroamine. Rhodococcus sp. strain DN22 was isolated by Coleman et al. (12) and was found to produce nitrite as a metabolite. Fournier et al. (19) found that DN22 also produces the metabolites ammonia, nitrous oxide, formaldehyde, carbon dioxide, and a dead-end product with a molecular weight of 119 that was later identified as 4-nitro-2,4-diazabutanal by Bhushan et al. (7). Fournier et al. (19) also proposed a pathway for aerobic RDX degradation in which denitration occurs, followed by spontaneous ring cleavage. Further experiments determined that the enzyme responsible for the degradation of RDX by DN22 is a cytochrome P450 enzyme (7, 13). Rhodococcus rhodochrous strain 11Y, which was isolated by SethSmith et al. (33), was found to produce the metabol...

Unusual Spectroscopic and Ligand Binding Properties of the Cytochrome P450-Flavodoxin Fusion Enzyme XplA

“…It is an example of a growing class of P450 enzymes fused to redox partners or other protein modules, with a flavodoxin domain attached at the N-terminal of the XplA P450 (15,22). The xplA gene was identified in several types of bacteria able to oxidatively exploit RDX as a source of nitrogen (61,62). XplA and its FAD-binding reductase partner XplB appear to be plasmid-encoded, along with several other genes involved in transport and degradation of RDX (63).…”

Involvement of cytochrome c CymA in the anaerobic metabolism of RDX by Shewanella oneidensis MR-1

“…strain KTR4 and Gordonia sp. strain KTR9 (Thompson et al 2005). RDX was also used as the sole N source for the anaerobic growth of Desulfovibrio spp.…”

Nitramine anion fragmentation: A mass spectrometric and Ab initio study

“…The biodegradation of RDX has been studied under a number of different conditions in the hopes of identifying cost-effective methods of remediating explosives-contaminated sites [7][8][9][10][11][12][13]. One of the major anaerobic metabolism pathways involves the sequential reduction of the exocyclic nitro to nitroso groups [7,8] to form three distinct metabolites that contain up to three nitrogen-nitrosonitrogen bonds: hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexhydro-1,3,5-trinitroso-1,3,5-triazine (TNX).…”