Defusing the environment: Engineering plants to degrade explosives.

Environmental contamination by explosives resulting from the manufacture, disposal and testing of munitions has led to increasing concern. Due to their toxic and mutagenic effects explosives are considered to be a major hazard to biological systems. Interest on the bioremediation of land contaminated with explosives has recently been focused on phytoremediation. While plants have many advantages over bacteria for the remediation of contaminated land and water, they lack the catabolic versatility which microorganisms have evolved. In order to yield an optimal system for in situ bioremediation of explosive residues in soil we sought to combine the impressive biodegradative capabilities of soil bacteria with the high biomass and stability of plants. Our investigation into the degradation of explosive residues by soil bacteria resulted in the isolation of Enterobacter cloacae PB2, which is capable of utilising nitrate ester explosives such as pentaerythritol tetranitrate (PETN) and nitroglycerin (GTN) as the sole source of nitrogen for growth. We have generated transgenic tobacco plants expressing PETN reductase and characterised them with regard to explosive degradation. The transgenic plants were shown to germinate and grow at concentrations of explosives inhibitory to wildtype plants, and exhibited enhanced degradation of 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.