Anaerobic Biodegradation of Hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) and Trichloroethylene (TCE): Single-and Dual-contaminant Batch Tests (original) (raw)
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Biodegradation of Hexahydro-1, 3, 5-Trinitro-1, 3, 5-Triazine
Applied and …
In previous work, we found that an anaerobic sludge efficiently degraded hexahydro-1,3,5-trinitro-1,3,5triazine (RDX), but the role of isolates in the degradation process was unknown. Recently, we isolated a facultatively anaerobic bacterium, identified as Klebsiella pneumoniae strain SCZ-1, using MIDI and the 16S rRNA method from this sludge and employed it to degrade RDX. Strain SCZ-1 degraded RDX to formaldehyde (HCHO), methanol (CH 3 OH) (12% of total C), carbon dioxide (CO 2) (72% of total C), and nitrous oxide (N 2 O) (60% of total N) through intermediary formation of methylenedinitramine (O 2 NNHCH 2 NHNO 2). Likewise, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) was degraded to HCHO, CH 3 OH, and N 2 O (16.5%) with a removal rate (0.39 mol ⅐ h ؊1 ⅐ g [dry weight] of cells ؊1) similar to that of RDX (0.41 mol ⅐ h ؊1 ⅐ g [dry weight] of cells ؊1) (biomass, 0.91 g [dry weight] of cells ⅐ liter ؊1). These findings suggested the possible involvement of a common initial reaction, possibly denitration, followed by ring cleavage and decomposition in water. The trace amounts of MNX detected during RDX degradation and the trace amounts of hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine detected during MNX degradation suggested that another minor degradation pathway was also present that reduced ONO 2 groups to the corresponding ONO groups.
FEMS Microbiology Ecology, 2000
Five obligate anaerobes that were most closely related to Clostridium bifermentans, Clostridium celerecrescens, Clostridium saccharolyticum, Clostridium butyricum and Desulfovibrio desulfuricans by their 16S rRNA genes sequences were isolated from enrichment cultures using hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as a nitrogen source. The above isolates transformed RDX at rates of 24.0, 5.4, 6.2, 2.5, 5.5 Wmol h 31 g (dry weight) of cells 31 , respectively, to nitrite, formaldehyde, methanol, and nitrous oxide. The present results indicate that clostridia are major strains responsible for RDX removal, and all isolates seemed to mainly transform RDX via its initial reduction to MNX and subsequent denitration. Since clostridia are commonly present in soil, we suggest that they may contribute to the removal of RDX in the subsurface (anoxic) soil.
Letters in Applied Microbiology, 2010
Aim: The goal of this study was to compare the degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by three Rhodococcus strains under anaerobic, microaerophilic (<0AE04 mg l)1 dissolved oxygen) and aerobic (dissolved oxygen (DO) maintained at 8 mg l)1) conditions. Methods and Results: Three Rhodococcus strains were incubated with no, low and ambient concentrations of oxygen in minimal media with succinate as the carbon source and RDX as the sole nitrogen source. RDX and RDX metabolite concentrations were measured over time. Under microaerophilic conditions, the bacteria degraded RDX, albeit about 60-fold slower than under fully aerobic conditions. Only the breakdown product, 4-nitro-2,4-diazabutanal (NDAB) accumulated to measurable concentrations under microaerophilic conditions. RDX degraded quickly under both aerated and static aerobic conditions (DO allowed to drop below 1 mg l)1) with the accumulation of both NDAB and methylenedinitramine (MEDINA). No RDX degradation was observed under strict anaerobic conditions. Conclusions: The Rhodococcus strains did not degrade RDX under strict anaerobic conditions, while slow degradation was observed under microaerophilic conditions. The RDX metabolite NDAB was detected under both microaerophilic and aerobic conditions, while MEDINA was detected only under aerobic conditions. Impact and Significance of the Study: This work confirmed the production of MEDINA under aerobic conditions, which has not been previously associated with aerobic RDX degradation by these organisms. More importantly, it demonstrated that aerobic rhodococci are able to degrade RDX under a broader range of oxygen concentrations than previously reported.
Letters in Applied Microbiology, 2010
Microaerophillic degradation of hexahydro-1,3,5-trinitro-1,3,5triazine (RDX) by three Rhodococcus strains Fuller, M. E.; Perreault, N.; Hawari, J.
Applied and Environmental Microbiology, 2016
ABSTRACTKinetic isotopic fractionation of carbon and nitrogen during RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) biodegradation was investigated with pure bacterial cultures under aerobic and anaerobic conditions. Relatively large bulk enrichments in15N were observed during biodegradation of RDX via anaerobic ring cleavage (ε15N = −12.7‰ ± 0.8‰) and anaerobic nitro reduction (ε15N = −9.9‰ ± 0.7‰), in comparison to smaller effects during biodegradation via aerobic denitration (ε15N = −2.4‰ ± 0.2‰).13C enrichment was negligible during aerobic RDX biodegradation (ε13C = −0.8‰ ± 0.5‰) but larger during anaerobic degradation (ε13C = −4.0‰ ± 0.8‰), with modest variability among genera. Dual-isotope ε13C/ε15N analyses indicated that the three biodegradation pathways could be distinguished isotopically from each other and from abiotic degradation mechanisms. Compared to the initial RDX bulk δ15N value of +9‰, δ15N values of the NO2−released from RDX ranged from −7‰ to +2‰ during aerobic b...
Soil Biology & Biochemistry, 1998
An aerobic, Gram-positive bacterium was isolated from explosives-contaminated soil by enrichment culture, using the nitramine explosive, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), as the sole added N source. The organism, identified by 16S rDNA analysis as a Rhodococcus sp., strain DN22, grew exponentially with a mean generation time of 6.5 h at 25°C in minimal medium containing RDX as the sole N source. The growth medium was depleted of RDX 24 h after inoculation but growth did not cease until 20 h later. It was concluded that strain DN22 was using NO−2, released from RDX, as a growth substrate because, following inoculation of strain DN22 into RDX-containing minimal medium, the concentration of NO−2 increased during the first 10 h of incubation and declined to undetectable amounts 20 h later. The ratio of the growth yields of strain DN22 grown on RDX or NO−3 as N sources indicated that three of the six N atoms of RDX were being incorporated into biomass. Increased concentrations of NH+4 in the growth medium reduced the extent of RDX degradation. Nitrite was produced from RDX by resting cell suspensions grown on RDX, NO−3, NO−2 or glutamine as N sources, but not by cells grown on NH+4–N or in peptone-yeast extract medium. Resting cells grown on RDX showed the highest degradative activity, compared to cells grown on alternative N sources, indicating that the RDX degradation system is inducible. When soil was inoculated with RDX-grown cells of strain DN22rr, a rifampicin-resistant derivative of strain DN22, there was significant biodegradation of RDX. The addition of oat chaff to soil stimulated the growth of strain DN22rr and enhanced biodegradation of RDX, resulting in 90% degradation of the explosive in 21 d.
Water, 2021
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) a nitramine explosive, which has contaminated various military sites during its use, storage and manufacturing worldwide. As RDX is a recalcitrant, less soluble and toxic to human beings and other organisms, it is essential to remediate the contaminated sites. In the current investigation, authors have explored the potential of two indigenous microbes i.e., Bacillus toyonensis (isolate No. WS4-TSB-3, MTCC No. 12857) and Paenibacillus dendritiformis (isolate No. S10-TSA-3, MTCC No. 12859) isolated from an explosive manufacturing facility in north India, for the degradation of RDX in aqueous medium. Furthermore, RDX degradation has been optimized using response surface methodology (RSM) in a 15 days experiment at concentration of 20, 40, and 60 mg/L. It was found that various factors such as initial concentration of RDX, inoculum volume (2, 4 and 6%) and time (5, 10 and 15 days) had impact on transformation and degradation of contaminant. ...
Environmental Toxicology and Chemistry, 2001
The metabolic fate of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in a mixed culture incubated under methanogenic conditions was studied. Analysis by high-performance liquid chromatography (HPLC) confirmed the loss of RDX and the formation of mono-, di-, and trinitroso-RDX as transient biodegradation intermediates. An additional peak observed in the HPLC chromatograms was identified by liquid chromatography-mass spectrometry as hydroxylamino-dinitroso-1,3,5-triazine. This is the first report identifying hydroxylamino-dinitroso-1,3,5-triazine as a transient intermediate produced during the anaerobic biodegradation of RDX.
Applied and Environmental Microbiology, 2002
indicating that two of the three N atoms in the metabolite originated from the ring in RDX. When [U-14 C]-RDX was used in the experiment, 64% of the original radioactivity in RDX incorporated into the metabolite with a molecular weight (MW) of 119 (high-pressure LC/radioactivity) and 30% in 14 CO 2 (mineralization) after 4 days of incubation, suggesting that one of the carbon atoms in RDX was converted to CO 2 and the other two were incorporated in the ring cleavage product with an MW of 119. Based on the above stoichiometry, we propose a degradation pathway for RDX based on initial denitration followed by ring cleavage to formaldehyde and the dead end product with an MW of 119. This is NRCC publication number 44634.