Electron shuttle-stimulated RDX mineralization and biological production of 4-nitro-2,4-diazabutanal (NDAB) in RDX-contaminated aquifer material

• Published in: Biodegradation (Dordrecht) 2010-11, Vol.21 (6), p.923-937
• Main Authors: Kwon, Man Jae, Finneran, Kevin T
• Format: Article
• Language: English
• Subjects: Acetates; Aldehydes - metabolism; Aquatic Pollution; Aquifers; Aza Compounds - metabolism; Bacteria - growth & development; Bacteria - metabolism; Biodegradation; Biodegradation of pollutants; Biodegradation, Environmental; Biological and medical sciences; Biomedical and Life Sciences; bioremediation; Biotechnology; Carbon Radioisotopes; Cyclic nitramine explosives; Electron shuttling; Electron Transport; Electrons; Environment and pollution; Fe(III) reducing microorganisms; Formaldehyde; Fundamental and applied biological sciences. Psychology; Geochemistry; Humic acid; Industrial applications and implications. Economical aspects; Iron; Iron - metabolism; Life Sciences; Metabolic Networks and Pathways; Metabolites; Microbial activity; Microbiology; Microorganisms; Mineralization; Minerals; Minerals - metabolism; Molecular Sequence Data; Original Paper; Oxidation-Reduction; Phylogeny; RNA, Ribosomal, 16S - genetics; Sediments (Geology); Soil Science & Conservation; Sulfate reduction; Sulfates; Terrestrial Pollution; Time Factors; Triazines - chemistry; Triazines - metabolism; Waste Management/Waste Technology; Waste Water Technology; Water Management; Water Pollutants, Chemical - metabolism; Water Pollution Control
• ISSN: 0923-9820; 1572-9729
• DOI: 10.1007/s10532-010-9352-1

The potential for extracellular electron shuttles to stimulate RDX biodegradation was investigated with RDX-contaminated aquifer material. Electron shuttling compounds including anthraquinone-2,6-disulfonate (AQDS) and soluble humic substances stimulated RDX mineralization in aquifer sediment. RDX mass-loss was similar in electron shuttle amended and donor-alone treatments; however, the concentrations of nitroso metabolites, in particular TNX, and ring cleavage products (e.g., HCHO, MEDINA, NDAB, and NH₄ ⁺) were different in shuttle-amended incubations. Nitroso metabolites accumulated in the absence of electron shuttles (i.e., acetate alone). Most notably, 40-50% of [¹⁴C]-RDX was mineralized to ¹⁴CO₂ in shuttle-amended incubations. Mineralization in acetate amended or unamended incubations was less than 12% within the same time frame. The primary differences in the presence of electron shuttles were the increased production of NDAB and formaldehyde. NDAB did not further degrade, but formaldehyde was not present at final time points, suggesting that it was the mineralization precursor for Fe(III)-reducing microorganisms. RDX was reduced concurrently with Fe(III) reduction rather than nitrate or sulfate reduction. Amplified 16S rDNA restriction analysis (ARDRA) indicated that unique Fe(III)-reducing microbial communities (β- and γ-proteobacteria) predominated in shuttle-amended incubations. These results demonstrate that indigenous Fe(III)-reducing microorganisms in RDX-contaminated environments utilize extracellular electron shuttles to enhance RDX mineralization. Electron shuttle-mediated RDX mineralization may become an effective in situ option for contaminated environments.