Transgenic switchgrass can decontaminate explosive residues

 

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is an explosive part of munitions extensively used by the military in training ranges having a global market size of around $10 billion.

This explosive does not degrade in the environment, it is absorbed into groundwater, and very toxic to soils organisms and humans. Therefore, an accumulation of the toxic material has happened, and cases of human contamination have been reported.

Not only active firing ranges are contaminated, but also manufacturing sites due to exhaustion plumes dump locations, minefields, and decommissioned sites. It is estimated that 10 million hectares of military land are contaminated in The United States. Since the armed forces continually need live-fire training, it is extremely important to have a permanent strategy to contain and remediate RDX.

There is a soil bacterium, Rhodococcus rhodochrous 11Y, that can degrade RDX. The genes responsible (xplA and xplB ) were identified and the breakdown of the explosive was understood. It was then proposed that a transgenic grass carrying these genes could be the solution for soil decontamination.

In the transgenic switchgrass, RDX is transformed into naturally occurring plant metabolites with no harvesting necessary. After promising results in the lab, a field trial was authorized in Fort Drum, New York with the condition that all flower heads were removed from the transgenic plants in the trial plots so no cross-breeding with native plants could occur.

There were three soil treatments (no RDX, 1mg kg^–1 RDX and 100mg kg^–1 RDX) and three vegetation treatments (no plant control (NPC), wild-type untransformed switchgrass (WT) and XplA/XplB-expressing switchgrass (TG)) replicated three times for a total of 27 plots.

RDX was not detected in any of the tissues sampled from the transgenic lines over the third growing season and across all three plots treated with the highest concentration. In 3 years of observation, the concentration of RDX in water from the transgenic plots was always less than either control and significantly less than the no plant control. The XplA/XplB-expressing plants took up and metabolized equivalent to an RDX removal rate of 27 kg ha^–1.

It was then confirmed that the transgenic switchgrass is capable of remediation and a transformation method for another grass (Pascopyrum smithii) native to many states in the US was developed as well. This looks to be a cost-effective and sustainable strategy to prevent groundwater contamination around military ranges.

By Rosana Segatto

Reference

Cary, T.J., Rylott, E.L., Zhang, L. et al. Field trial demonstrating phytoremediation of the military explosive RDX by XplA/XplB-expressing switchgrass. Nat Biotechnol (2021). https://doi.org/10.1038/s41587-021-00909-4

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Field trial demonstrating phytoremediation of the military explosive RDX by XplA/XplB-expressing switchgrass | Nature Biotechnology