Isolation and characterization of RDX-degrading <Emphasis Type="Italic">Rhodococcus</Emphasis> species from a contaminated aquifer |
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Authors: | Anat Bernstein Eilon Adar Ali Nejidat Zeev Ronen |
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Institution: | (1) Department of Environmental Hydrology and Microbiology, Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990 Beer Sheva, Israel;(2) Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel; |
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Abstract: | Groundwater contamination by the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a global problem. Israel’s coastal
aquifer was contaminated with RDX. This aquifer is mostly aerobic and we therefore sought aerobic bacteria that might be involved
in natural attenuation of the compound in the aquifer. RDX-degrading bacteria were captured by passively sampling the indigenous
bacteria onto sterile sediments placed within sampling boreholes. Aerobic RDX biodegradation potential was detected in the
sediments sampled from different locations along the plume. RDX degradation with the native sampled consortium was accompanied
by 4-nitro-2,4-diazabutanal formation. Two bacterial strains of the genus Rhodococcus were isolated from the sediments and identified as aerobic RDX degraders. The xplA gene encoding the cytochrome P450 enzyme was partially (~500 bp) sequenced from both isolates. The obtained DNA sequences
had 99% identity with corresponding gene fragments of previously isolated RDX-degrading Rhodococcus strains. RDX degradation by both strains was prevented by 200 μM of the cytochrome P450 inhibitor metyrapone, suggesting
that cytochrome P450 indeed mediates the initial step in RDX degradation. RDX biodegradation activity by the T7 isolate was
inhibited in the presence of nitrate or ammonium concentrations above 1.6 and 5.5 mM, respectively (100 mg l−1) while the T9N isolate’s activity was retarded only by ammonium concentrations above 5.5 mM. This study shows that bacteria
from the genus Rhodococcus, potentially degrade RDX in the saturated zone as well, following the same aerobic degradation pathway defined for other
Rhodococcus species. RDX-degrading activity by the Rhodococcus species isolate T9N may have important implications for the bioremediation of nitrate-rich RDX-contaminated aquifers. |
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