Christopher E. French

Engineering plants for the phytodetoxification of explosives

SummaryWidespread contaimination 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.

Engineering pathways for transformations of morphine alkaloids

Semisynthetic opiates provide some of the most potent analgesic compounds currently in clinical use, the majority of which are synthesized from the naturally occurring alkaloids morphine, codeine and thebaine. The use of recombinant DNA technology to engineer pathways for the biological synthesis of semisynthetic opiate drugs could offer significant advantages over existing chemical methods and may, ultimately, provide novel biosynthetic routes for the development of new therapeutics.

Uptake and Metabolism of TNT and GTN by Plants Expressing Bacterial Pentaerythritol Tetranitrate Reductase

The manufacture and improper disposal of explosives has resulted in a significant amount of land requiring remediation. The compound 2,4,6-trinitrotoluene (TNT) is the most persistent and toxic of the explosive pollutants with current treatment methods being energy intensive and costly. Bacterial enzymes such as pentaerythritol tetranitrate reductase (PETNR) from Enterobacter cloacae PB2 have been found to have activity against TNT; however, microbes often lack the biomassnecessary for remediation applications. The PETNRgene (onr1) was transformed into tobacco plants in an attempt to combine the metabolic diversity of microbes with the sequestering properties of plants. The resulting transgenic plants were shown to have enhanced tolerance to TNT during germination and as seedlings. Phytoremediation applications with these plants may provide an alternative treatment of TNT contamination.

The Degradation of Nitrate Ester Explosives and TNT by Enterobacter Cloacae PB2

One of the major environmental problems facing the military establishment is the considerable amount of land and water that is contaminated with explosives, particularly TNT (2,4,6-trinitrotoluene). Explosives are found in the environment as a result of waste water produced by manufacturing plants and from the disposal of off-specification material or demilitarisation of out-of-date munitions. Concerns have arisen regarding the toxicity and environmental fate of TNT and nitrate ester explosives such as PETN (pentaerythritol tetranitrate) and GTN (glycerol trinitrate) due to their relative toxicity. PETN and GTN are produced in large amounts for use as explosives in blasting caps and detonators and as vasodilators for the control of angina. Nitrate esters are extremely rare in nature and multiply-substituted nitrate esters are not known to occur naturally. The environmental fate of such compounds which are produced in large quantities by the chemical industries, is therefore of considerable interest. In this paper we describe the isolation and characterisation of a strain of Enterobacter cloacae from explosives contaminated soilt that is capable of utilising nitrate ester explosives and TNT as sole nitrogen sources for growth.