| Soil contamination from nitro-organic explosives such as 2,4,6-trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, and HMX poses a significant risk to human health and that of the surrounding eco-system. Removal of contaminants can be accomplished through soil washing, incineration, and chemical techniques and/or bioremediation. The current study focused on the characterization of microbes present in soils, obtained from an artillery firing range, that contained significant levels of nitroorganic explosives. Direct examination of metagenomic bacterial DNA extracted from soil samples was achieved using the 16S rRNA gene as a target for bacterial identification. The 16S rRNA gene was used to identify bacteria present in a bioreactor treated soil sample contaminated with nitro-organic explosives. The community structure was evaluated over a 90 day period with and without the addition of supplementary bacterial nutrients. The results were compared to previously reported results of bacteria capable of degrading these contaminants. Differences in the microbial community structure were noted between different bioreactor treatments, nucleic acid extractions, and bioreactor vessels. Soil was initially contaminated to the greatest extent with HMX, and possible TNT metabolites were also identified in the initial soil sample. Soil samples from control bioreactor runs showed no genera present in proportions greater than 10%, except at day 45 samples from the second bioreactor, which was largely inhabited by members of the genus Methylotenera. Fingerprints obtained from nutrient addition soil samples showed a significant presence of the genus Nitrosospira. The phylum Acidobacteria increased in abundance throughout the bioreactor treatments, and its abundance was previously reported to be inversely proportional to TNT concentration in the soil. None of the previously reported genera capable of degrading nitro-explosives were found in the soil microbial fingerprints. These genera may be present in lower abundance and would be detected with additional sampling. Phenomena such as horizontal gene transfer may allow for nitro-organic explosive degradation by bacteria that were not previously reported. |
