| The prevention of groundwater contamination with RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) from live-fire military range soils is a priority of the U.S. Department of Defense. In situ microbial degradation is a potential method for treating contaminated sites to prevent the migration of RDX offsite. Several Rhodococcus sp. and closely related bacteria have been isolated with a novel cytochrome P450, XplA, capable of using RDX as a sole nitrogen source aerobically. The research presented here combines cultivation techniques with culture independent stable isotope probing (SIP) to identify new xplA-bearing organisms from contaminated soils. These efforts have led to the most diverse collection of xplA-bearing bacteria currently in isolation and include the only two isolates outside of the family Nocardiaceae, and the only reported RDX-degraders isolated from a military training range. Molecular analyses of isolated RDX-degraders provided direct evidence that the xplA gene is located on mobile genetic elements and has likely disseminated globally through lateral gene transfer. SIP analyses of RDX degrading range soils verified that xplA-organisms were responsible for RDX degradation in the soils when labile carbon was supplied. Microcosm experiments with the range grass, western wheatgrass (Pascopyrum smithii), demonstrated that RDX degradation in range soils can be stimulated by plant rhizospheres. These experiments validate that microbial RDX degraders are present on military ranges and lay a foundation for the further development of RDX bioremediation studies. |
