Biodegradation of RDX and MNX with <i>Rhodococcus</i> sp. Strain DN22: New Insights into the Degradation Pathway

Halasz, Annamaria; Manno, Dominic; Strand, Stuart E.; Bruce, Neil C.; Hawari, Jalal

doi:10.1021/es1023724

Cited by 25 publications

(7 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previous reports also indicated no significant C isotopic fractionation during aerobic biodegradation (19). From a mechanistic perspective, the enrichment in 15 N and lack of enrichment in 13 C during aerobic RDX degradation are consistent with the initial enzymatic attack by the P450 XplA enzyme on an NON bond in the RDX structure (47), rather than a COH bond, as has also been postulated (7,48). Consistent 15 N enrichment during aerobic biodegradation by all cultures so far examined indicates that isotopic analysis of N isotope ratios in RDX may be a useful tool to detect aerobic degradation of RDX in situ.…”

Section: Discussionsupporting

confidence: 82%

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Fuller

Heraty

Condee

et al. 2016

Appl Environ Microbiol

View full text Add to dashboard Cite

Kinetic 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 in 15 ؊ production were much larger than, but systematically related to, the bulk RDX N isotope effects with different bacteria. Apparent intrinsic 15 N-NO 2 ؊ values were consistent with an initial denitration pathway in the aerobic experiments and more complex processes of NO 2 ؊ formation associated with anaerobic ring cleavage. These results indicate the potential for isotopic analysis of residual RDX for the differentiation of degradation pathways and indicate that further efforts to examine the isotopic composition of potential RDX degradation products (e.g., NO x ) in the environment are warranted. IMPORTANCEThis work provides the first systematic evaluation of the isotopic fractionation of carbon and nitrogen in the organic explosive RDX during degradation by different pathways. It also provides data on the isotopic effects observed in the nitrite produced during RDX biodegradation. Both of these results could lead to better understanding of the fate of RDX in the environment and help improve monitoring and remediation technologies. Explosives manufacturing, testing, and training range activities have resulted in the release of explosive compounds, including the nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), in soils at numerous U.S. Department of Defense (DoD) installations. Because RDX is mobile in soils and persistent, it has also been detected in groundwater or drinking water at some of these sites (1, 2).There has been extensive research examining the biological degradation of explosive compounds by pure cultures of bacteria as well as mixed consortia (for a review, see reference 3). RDX biodegradation has been observed under a range of redox conditions (4-9), and at least three predominant degradation pathways have been elucidated (Fig. 1). Typically, RDX is degraded anaerobically as an electron acceptor, requiring a carbon source as an electron donor, and entails either successive reduction of the three nitro groups via successive two-electron (2e Ϫ ) transfers followed by ring cleavage (pathway A) or an earlier opening of the ring structure (pathway B1), with or without initial denitration (pathway B2). The specific mechanism of ring destabilization and the steps that lead to ring cleavage may be variable and remain subject to debate (6,7,10). A denitration reaction that converts hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) (in pathway A) through multiple intermediates to methylenedinitramine (MEDINA) (in pathway B) under anaerobic conditions has also been proposed (7,11,12). Aerobic degradation proceeds via two single-electron transfer steps resulting in sequential denitration (2 NO 2 Ϫ removed) followed by ring cleavage and production of 4-nitro-2,4-diazabutanal (NDAB) (pathway C) (7). Some bacteria are able to utilize R...

show abstract

Section: Discussionsupporting

confidence: 82%

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Fuller

Heraty

Condee

et al. 2016

Appl Environ Microbiol

View full text Add to dashboard Cite

show abstract

“… , Biodegradation under oxic conditions and alkaline hydrolysis pathways have both been suggested to denitrate RDX to a dinitro-1,3,5-triazacyclohex-1-ene intermediate ( 3 in Scheme ). ,,,,− While the enzymatic reaction involves oxidation of the methylene carbon, the hydrolysis pathway proceeds as a base-catalyzed deprotonation and elimination of nitrite. These mechanistic differences are also manifested in distinct C and N isotope fractionation behavior, with ε N between −2.1 and −2.4‰ as well as negligible ε C for enzymatic oxidation vs ε N of −7.8‰ and ε C −5.3‰ for the HNO 2 elimination. ,, …”

Section: Introductionmentioning

confidence: 99%

Exploring the Utility of Compound-Specific Isotope Analysis for Assessing Ferrous Iron-Mediated Reduction of RDX in the Subsurface

Tong

Berens

Ulrich

et al. 2021

Environ. Sci. Technol.

View full text Add to dashboard Cite

Subsurface contamination with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) at ordnance production and testing sites is a problem because of the persistence, mobility, and toxicity of RDX and the formation of toxic products under anoxic conditions. While the utility of compound specific isotope analysis for inferring natural attenuation pathways from stable isotope ratios has been demonstrated, the stable isotope fractionation for RDX reduction by ironbearing minerals remains unknown. Here, the N isotope fractionation of RDX during reduction by Fe(II) associated with Fe minerals and natural sediments was evaluated and applied to the assessment of mineral-catalyzed RDX reduction in a contaminant plume and in sediment columns treated by in-situ chemical reduction. Laboratory studies revealed that RDX was reduced to nitroso compounds without denitration and the concomitant ring cleavage. Fe(II)/iron oxide mineral-catalyzed reactions exhibited N isotope enrichment factors, εN, between -6.3±0.3‰ to -8.2±0.2‰ corresponding to an apparent 15 N kinetic isotope effect of 1.04-1.05.The observed variations of the δ 15 N of ~15‰ in RDX from groundwater samples suggested an extent of reductive transformation of 85% at an ammunition plant. Conversely, we observed masking of N isotope fractionation after RDX reduction in laboratory flow-through systems, which was presumably due to a limited accessibility to reactive Fe(II).

show abstract

“…Past studies have identified nitrite, NDAB, MEDINA (methylenedinitramine), and formamide to be nitrogenous degradation products of RDX-degradation. 9,11,21,41 These observations indicate metabolites from RDX may be available to bacteria in the soil that did not degrade RDX and may account for the 15 N assimilation by some of the labeled populations identified in our analyses. Thus, although our studies served to confirm the general a Estimated BDs, the G+C content was calculated for the 16S rRNA genes plus the fragment size listed on both sides of the genes.…”

Section: ■ Materials and Methodsmentioning

confidence: 74%

Identification of Microbial Populations Assimilating Nitrogen from RDX in Munitions Contaminated Military Training Range Soils by High Sensitivity Stable Isotope Probing

Andeer¹,

Stahl²,

Lillis³

et al. 2013

Environ. Sci. Technol.

Self Cite

View full text Add to dashboard Cite

The leaching of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) from particulates deposited in live-fire military training range soils contributes to significant pollution of groundwater. In situ microbial degradation has been proposed as a viable method for onsite containment of RDX. However, there is only a single report of RDX degradation in training range soils and the soil microbial communities involved in RDX degradation were not identified. Here we demonstrate aerobic RDX degradation in soils taken from a target area of an Eglin Air Force Base bombing range, C52N Cat's Eye, (Eglin, Florida U.S.A.). RDX-degradation activity was spatially heterogeneous (found in less than 30% of initial target area field samples) and dependent upon the addition of exogenous carbon sources to the soils. Therefore, biostimulation (with exogenous carbon sources) and bioaugmentation may be necessary to sustain timely and effective in situ microbial biodegradation of RDX. High sensitivity stable isotope probing analysis of extracted soils incubated with fully labeled (15)N-RDX revealed several organisms with (15)N-labeled DNA during RDX-degradation, including xplA-bearing organisms. Rhodococcus was the most prominent genus in the RDX-degrading soil slurries and was completely labeled with (15)N-nitrogen from the RDX. Rhodococcus and Williamsia species isolated from these soils were capable of using RDX as a sole nitrogen source and possessed the genes xplB and xplA associated with RDX-degradation, indicating these genes may be suitable genetic biomarkers for assessing RDX degradation potential in soils. Other highly labeled species were primarily Proteobacteria, including: Mesorhizobium sp., Variovorax sp., and Rhizobium sp.

show abstract

Biodegradation of RDX and MNX with Rhodococcus sp. Strain DN22: New Insights into the Degradation Pathway

Cited by 25 publications

References 45 publications

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Exploring the Utility of Compound-Specific Isotope Analysis for Assessing Ferrous Iron-Mediated Reduction of RDX in the Subsurface

Identification of Microbial Populations Assimilating Nitrogen from RDX in Munitions Contaminated Military Training Range Soils by High Sensitivity Stable Isotope Probing

Contact Info

Product

Resources

About