Towards engineering degradation of the explosive pollutant hexahydro-1,3,5-trinitro-1,3,5-triazine in the rhizosphere

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a serious environmental pollutant on military land. This compound is the most widely used explosive and pollution has arisen primarily as the result of military training, along with munition manufacturing and disassembly processes. This toxic explosive is recalcitrant to degradation in the environment and leaches rapidly into groundwater, where accumulation in aquifers is threatening drinking water supplies (Clausen, etal., 2004). While plants have only limited degradative activity towards RDX, microorganisms, including Rhodococcus rhodochrous 11Y, have been isolated from contaminated land. Despite the presence of microbial RDX-metabolising activity in contaminated soils, the persistence of RDX in leachate from contaminated soil indicates that this activity or biomass is insufficient, limiting its use to remediate polluted soils. Bacterial activity in the rhizosphere is of magnitudes greater than in the surrounding soil, and the roots of grass species on training ranges in the United States are known to penetrate deeply into the soil, producing a compact root system and providing an ideal environment to support the capture of RDX by microorganisms in the rhizosphere. Here, we have investigated the ability of the root-colonising bacterium Pseudomonas fluorescens, engineered to express XplA, to degrade RDX in the rhizosphere.