Metabolism of the Aliphatic Nitramine 4-Nitro-2,4-Diazabutanal by Methylobacterium sp. Strain JS178

Abstract

The aliphatic nitramine 4-nitro-2,4-diazabutanal (NDAB; C 2 H 5 N 3 O 3 ) is a ring cleavage metabolite that accumulates during the aerobic degradation of the energetic compound hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by various Rhodococcus spp. NDAB is also produced during the alkaline hydrolysis of either RDX or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and during the photolysis of RDX. Traces of NDAB were observed in a soil sampled from an ammunition-manufacturing facility contaminated with both HMX and RDX, suggesting natural attenuation. In this study, we report the isolation of a soil bacterium that is able to degrade NDAB under aerobic conditions. The isolate is a pink-pigmented facultative methylotroph affiliated with the genus The cyclic nitramines hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (Fig. 1) are toxic energetic compounds that have caused severe soil and groundwater contamination (4). A good understanding of the microbial processes at contaminated sites is important in order to evaluate the fate of the compounds during natural attenuation. The mechanisms of transformation of RDX and HMX under anaerobic conditions have been well established (12). Although no aerobic bacteria are reported to degrade HMX, several aerobic bacteria have been isolated based on the ability to use RDX as a sole nitrogen source. Among these, three rhodococci have been reported: Rhodococcus sp. strain A (14), Rhodococcus sp. strain DN22 (5), and Rhodococcus rhodochrous strain 11Y (18). The initial denitration of the RDX molecule by rhodococci requires the involvement of a cytochrome P-450 (3, 6, 18). Denitration is followed by ring cleavage and the production of nitrous oxide (N 2 O), ammonia (NH 3 ), formaldehyde (HCHO), and a dead-end product identified as 4-nitro-2,4-diazabutanal (NDAB) (Fig. 1) (8). The carbon stoichiometry clearly indicates that rhodococci mineralize 30 to 33% of the RDX (estimated as liberated CO 2 ) and that 62 to 64% of the remaining carbon accumulates as NDAB (8). NDAB is a transient intermediate during the degradation of HMX by the white-rot fungus Phanerochaete chrysosporium and is also produced during alkaline hydrolysis or photolysis of cyclic nitramines (10, 13). The widespread production of NDAB, via a variety of biotic and abiotic processes, underlines the environmental importance of this compound. Moreover, NDAB was present in soil contaminated with both HMX and RDX, signifying that its detection at contaminated sites might provide an effective method of monitoring natural attenuation (9). Because the aliphatic nitramine is highly soluble in water and does not sorb to soil particles, NDAB has a considerable potential to migrate offsite in surface waters or groundwater (9). This explains why NDAB was not reported to accumulate in soil. The results to date indicate that NDAB is degraded poorly, if at all, by soil microbes.The genus Methylobacterium, belonging to the Alphaproteobacteria, is composed of a variety...

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

“…RDX and its N-nitroso derivatives are toxic (Zhang et al 2006;Pan et al 2007). On the other hand, the ring-cleavage product MEDINA is unstable and decomposes to HCHO or CO 2 and N 2 O , while NDAB can be degraded and mineralized by microorganisms such as Methylobacterium and Phanerochaete chrysosporium (Fournier et al 2004(Fournier et al , 2005. As already discussed, CymA is involved in the reduction of several natural substrates.…”

Microbially Mediated Biodegradation of Hexahydro-1,3,5-Trinitro-1,3,5- Triazine by Extracellular Electron Shuttling Compounds

“…RDX will biodegrade aerobically in the presence of specific microorganisms (14), but specialized enrichment conditions are required for these organisms to proliferate (4), and several reports suggest limited degradation kinetics (19,60). Aerobic bioremediation is possible in shallow soil or groundwater that has sufficient oxygen but is technically difficult in groundwater that has become anaerobic.…”

Biotransformation of N -Nitrosodimethylamine by Pseudomonas mendocina KR1

“…Analytical methods. NDMA, NTDMA, and NTMA were analyzed using the high-pressure liquid chromatography method previously developed for the quantification of nitro-2,4-diazabutanal, a key metabolite of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) biotransformation under aerobic conditions (5,6). Analyses of nitrate (NO 3 Ϫ ), nitrite (NO 2 Ϫ ), formate (HCOO Ϫ ), formaldehyde (HCHO), and methanol (CH 3 OH) were performed as previously reported (2,11).…”