The role of nutrients in the biodegradation of 2,4,6-trinitrotoluene in liquid and soil.

The widely used explosive 2,4,6-trinitrotoluene (TNT) has residues that are potentially explosive, toxic, and mutagenic. TNT and other explosives can be degraded by microorganisms; however, biostimulation is needed for process efficiency. To investigate the effectiveness of using biostimulation to degrade TNT, we added varying concentrations of a nutrient amendment consisting of inorganic salts, plant extracts, and molasses to soil and liquid media. For the inoculum we used a consortium of bacteria AM 06 that had exhibited the ability to degrade TNT and which had been previously isolated from explosives-contaminated soils. Phylogenetically, the clones clustered into seven different genera: Klebsiella, Raoultella, Serratia, Stenotrophomonas, Pseudoxanthomonas, Achromobacter and Pseudomonas. The addition of AM 06 consortium to a liquid environment along with 100% nutrient amendment decreased the amount of TNT (and its degradation products) by up to 90% after 14 days incubation. At the total amount of TNT was less than 100 mg/l, the concentration of TNT did not influence the amount of sugar consumed by the bacteria consortium. In soil media, the TNT degradation process was dependent on the concentration of nutrient amendment added. At higher initial concentrations of TNT (500 mg/kg), bioaugmentation (i.e., addition of bacteria inoculum) had a demonstrated effect, especially when nutrient concentrations of 50% and 100% were added to the soil. Findings of this study could further the understanding of the TNT biodegradation processes in water and soil and provide for optimization of the technological conditions for bioremediation.

Effect of plant extract on the degradation of nitroaromatic compounds by soil microorganisms.

Remediation of soils contaminated by nitroaromatic compounds and nitramines, i.e. explosives, is known as very important, complicated, and rapidly developing area of biotechnology. A search for optimal growth conditions for soil bacteria is of a great importance in order to isolate various xenobiotic degraders. Bacteria consortium A43 was isolated from soils contaminated with explosives. In the presence of carbohydrate and plant extract, an addition of TNT to the solidified minimal medium stimulated the growth of the tested bacteria, as compared to other bacteria consortium isolated from the same soils. Reducing sugars as carbohydrates, and cabbage leaf extract as a plant extract were used in these experiments. Cultivation of the A43 in liquid medium of the same content showed that addition of cabbage leaf extract alone to medium is much more efficient for TNT degradation by growing biomass as compared to addition of carbohydrate alone.