Biodegradation of 2, 4, 6-Trinitrotoulene (TNT), Pentaerythritol Tetranitrate (PETN) & Pentolite by environmental microbes

The nitroaromatic compound 2, 4, 6-trinitrotoluene (TNT) and the nitrate esters glycerol trinitrate (GTN) and pentaerythritol tetranitrate (PETN) are high explosives that have been produced on a massive scale for use in industrial and military applications. Through many years of production and use of these explosives, large quantities of toxic wastes have been generated, which has resulted in extensive contamination of soil and groundwater. These organic nitrate contaminants are highly recalcitrant and not normally found in the environment, thus classifying these compounds as xenobiotics. During this study, 36 bacterial species were isolated from contaminated soil and water that were able to utilize either TNT or PETN as a sole source of nitrogen. These were identified as Arthrobacter sp. (Pa-3, Pb-5, ST12, ST13, ST14, ST17, ST23, ST26), Pseudomonas sp. (ST1, ST2, ST15, ST18, ST19,ST22), Enterobacter sp. (ST3, ST5, ST6, ST8 , ST11), Klebsiella sp. (ST4, ST10, ST16, ST20, ST21, ST28, ST29), Microbacterium sp. (ST7, Pa-4, Pb-6,ST9, ST24, ST25 ST27,ST30), and Achromobacter xylosoxidans (TNT1, TNT2). Six representative isolates were selected from the 36 isolates for further analysis of growth and enzyme activity. The isolates were found to catalyse the NAD(P)H- dependent reductive cleavage/breakdown of GTN and PETN in a manner that was similar to a class of previously described oxidoreuctase flavoproteins. These include Old Yellow Enzyme (OYE), PETN reductase, GTN reductase, xenobiotic reductases A and B and N-ethyl maleimide reductas. This is the first report of nitroaromatic degradation by Achromobacter xylosoxidans as per the author’s knowledge.<br><br>The aim of this study was to isolate bacteria able to degrade TNT and PETN and to characterize these bacteria and the enzymes produced by them. Thirty-six bacteria were isolated from contaminated soil and water that were able to utilize either TNT or PETN as a sole source of nitrogen. Identification was based on 16S rRNA gene sequences and biochemical testing.<br><br>Studies investigating co-metabolism of the explosives in the presence of Tween-80 was performed. Triton X-100 was also evaluated as co-metabolic substrate. It was demonstrated that the addition of Tween- 80 as a co-substrate assisted in the co-metabolism of explosives and did improve the growth and therefore the degradation of the explosive. However, Triton X-100 did not result in co-metabolism of the explosives since an improvement in growth was not observed.<br><br>The information acquired in this study can assist in the further characterization, optimization and production of explosive-degrading enzymes.<br>