Transformation of 2,4,6-trinitrotoluene (TNT) by Raoultella terrigena

Abstract

Manufacture of nitroorganic explosives generates toxic wastes leading to contamination of soils and waters, especially groundwater. For that reason bacteria living in environments highly contaminated with 2,4,6-trinitrotoluene (TNT) and other nitroorganic compounds were investigated for their capacity for TNT degradation. One isolate, Raoultella terrigena strain HB, removed TNT at concentrations between 10 and 100 mg l(-1) completely from culture supernatants under optimum aerobic conditions within several hours. Only low concentrations of nutrient supplements were needed for the cometabolic transformation process. Radioactivity measurements with ring-labelled (14)C-TNT detected about 10-20% of the initial radioactivity in the culture supernatant and the residual 80-90% as water-insoluble organic compounds in the cellular pellet. HPLC analysis identified aminodinitrotoluenes (2-ADNT, 4-ADNT) and diaminonitrotoluenes (2,4-DANT) as the metabolites which remained soluble in the culture medium and azoxy-dimers as the main products in the cell extracts. Hence, the new isolate could be useful for the removal of TNT from contaminated waters.

Combined biological–chemical procedure for the mineralization of TNT

“…The latter results can be explained by competing reactions of the intermediates as shown in Scheme 2. Similar results were obtained, when TNT was reduced by the bacteria Raoultella terrigena under aerobis conditions (Claus et al 2006).…”

“…However a more effective biological procedure would be needed to make such a procedure economically and ecologically advantageous over the presently used adsorption of the contaminants by charcoal. In this respect our recently described TNT degradation by the bacteria strain R. terrigena seems to be a good alternative (Claus et al 2006). This bacterium was shown to scavenge TNT from aqueous media and to maintain most of the material inside the cell in form of azooxy-dimers the formation of which is explained in Scheme 5.…”

Co-metabolic degradation of dimethoate by Raoultella sp. X1

“…In many cases, some of the key enzymes and cofactors responsible for transformation of the non-growth substrate and utilization of the obligated growth substrate are shared. Co-metabolism can be optimized by maintaining the proper ratio of growth to non-growth substrates (Jung and Park 2005;Kan and Deshusses 2006;Sui et al 2006;Claus et al 2007). Microbial co-metabolism of organic pollutants has drawn a great deal of attention because of its potential for high transformation rates, wide applicability to a broad range of compounds, and a requirement for an inexpensive and widely available primary growth substrate (Kim et al 2004;Frascari et al 2005).…”

TNT transformation products are affected by the growth conditions of Raoultella terrigena

“…By balancing the degradation reaction using 14 C-TNT, we found that some of the material could not be extracted from the cell pellet but was rather covalently bound to the organic matrix (Leung et al 1995). This entrapment may be exploited for the microbial remediation of TNT-contaminated waters (Claus et al 2006b). …”

“…Radioactivity measurements demonstrated that about 10-20% of the [ 14 C]TNT initially present remained in the culture supernatant, whereas the residual 80-90% was tightly associated with the cellular pellet. This entrapment may be used for the treatment of TNT-contaminated waters (Claus et al 2006b). However, occasionally we observed that the nutrient concentration in the culture media determined not only the transformation velocity, but also the nature and amounts of soluble and cellbound metabolites (Claus et al 2006a).…”