Engineering plants for the phytodetoxification of explosives

Widespread contamination of the environment by explosives resulting from the manufacture, disposal and testing of munitions is becoming a matter of increasing concern. Most explosives are considered to be a major hazard to biological systems due to their toxic and mutagenic effects. Interest on the bioremediation of land contaminated with explosives has recently been focused on phytoremediation. Unfortunately, whilst plants have many advantages for the remediation of contaminated land and water, they lack the catabolic versatility which enables microorganisms to mineralize such a wide diversity of xenobiotic compounds. This raised the interesting question as to whether the impressive biodegradative capabilities of soil bacteria could be combined with the high biomass and stability of plants to yield an optimal system for in situ bioremediation of explosive residues in soil. Our investigation into the degradation of explosive residues by soil bacteria resulted in the isolation of Enterobacter cloacae PB2, which is capable of utilizing nitrate ester explosives such as pentaerythritol tetranitrate (PETN) and nitroglycerin as the sole source of nitrogen for growth. We have successfully introduced PETN reductase, the enzyme initiating explosive degradation in this organism, into plants to create transgenic plants that degrade explosives. Since the bacterial degradative pathways for many classes of organic pollutant have been elucidated, this may be a generally applicable method of achieving bioremediation of contaminated soil in the environment.