Graduate Thesis Or Dissertation
 

Biotransformation of 2,4,6-trinitrotoluene by ruminal organisms

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  • 2,4,6-Trinitrotoluene (TNT) has been the common munitions used in the world and is an environmental contaminant that is amendable to reductive transformation reactions. The rumen is an extremely reductive environment containing diverse microbial populations. There are 21 pure culture ruminal bacteria species in culture collection, these were tested for the ability to degrade TNT. Of the 21 bacterial strains tested, 12 showed > 90% degradation of TNT, 5 strains showed 80-90% degradation, 3 strains only had low TNT degrading ability and one organism was completely inhibited by TNT concentrations of 100 mg/l. Of the 12 strains able to transform >90% of the TNT, 7 showed evidence of degradation of aminodinitrotoluene (ADNTs) and were subsequently tested for the ability to degrade ADNTs and diaminonitrotoluene (DANTs). Four were able to completely transform all these compounds, one was able to degrade all but 2,4-diaminonitrotoluene and the remaining two were able to degrade the ADNTs but were unable to transform the DANTs at a concentration of 50 mg/l. Degradation constants ranged from 0.31-11.39 h⁻¹ and the Michaelis-Menten constant ranged from 20-739 mg/l. Inhibition was detected for two of the organisms tested at levels of TNT higher than 50 mg/l. In order to determine the effect of TNT on rumen bacterial populations, rumen fluid was collected from three sheep before and after feeding TNT at a dose of 35.5 mg/day and compared to a control animal. Clone libraries were constructed for each rumen fluid sample and compared for changes in microbial populations. Several clones from the pre-TNT clustered with clones from the end of the experiment. The diversity and richness indices reveal that the number of clones sequenced were not enough to completely describe the populations found in the rumen. A limited number of shifts in populations between the pre- and post-treatment were detected within animals. However, there was no pattern in population fluxes detected in relationship to TNT treatment. These results indicate that a broad range of ruminal bacteria can degrade TNT and that feeding TNT at levels found in plant material to sheep does not affect the bacterial populations.
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