Enhancing Rhizosphere Bacterial Degradation of RDX


Soluble toxic compounds used in explosives are widely recognized as a significant barrier to the attainment of sustainable training ranges. The most serious of these problems is the movement of toxic munitions compounds, such as hexahydro-1,3,5-triazine (Royal Demolition Explosive, RDX), in groundwaters and surface waters outside the boundaries of the training ranges, threatening local water supplies and ecosystems. A sustainable solution to this problem must be inexpensive and self-maintaining. Microbial communities are known to use RDX as a source of nitrogen, but their natural activities in many soil and ground water environments are not sufficient to remove the toxic compounds to levels required by regulation. Because rhizosphere microbial communities have enhanced populations and activity compared to surrounding soils, and since specific microbial populations are associated with particular plant communities, manipulation of the plant community offers a way to enhance microbial degradation of RDX with a minimum of expense and maintenance.

We will characterize the bacteria in the rhizosphere by their relative access to carbon in plant root exudates and nitrogen in RDX, thus organizing the rhizosphere microbial community by its trophic structure and its ability to degrade RDX. Using this hierarchy, we will evaluate the position of RDX-degrading microorganisms in the rhizosphere trophic structure, and the details of their dependence on plant exudates. Armed with this knowledge, we will propose methods for choosing plants (and thereby microbial communities) that optimize RDX degradation in soils exposed to surface runoff from training ranges.

Our study will provide novel information about the structures and energetic relationships of microbial communities in plant rhizospheres, the identity and distributions of RDX degraders in the rhizosphere, the organic components of root exudates that support RDX degraders, and how genetic variability in training range plants may be used to select for RDX degraders in the rhizosphere.

Molecular probes developed in this study will be used to survey training range plant microbial communities for RDX-degraders. Understanding which root exudates enhance RDX-degrading populations will inform selection of native plants and design of genetically modified plants to increase rhizosphere degradation of RDX in training ranges.

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