Microbial characterization of TNT-contaminated soils and anaerobic TNT degradation: high and unusual denitration activity

2,4,6-trinitrotoluene (TNT) is one of the most common explosives. In spite of its known toxicity and mutagenicity for many organisms, soils and groundwater are still frequently contaminated at manufacturing, disposal and TNT-destruction sites. Thirteen soil samples collected from a TNT-destruction field were investigated for their concentrations of TNT and its derivatives as well as for their microbial diversity. They contained TNT at various concentrations, ranging from 4 to 36 g TNT/kg soil. Various metabolites were also detected, including 2,4,6-trinitrobenzaldehyde, 4-amino-2,6-dinitrotoluene, 2-amino-4,6-dinitrotoluene and 2,4-dinitrotoluene. Microbial communities of these soil samples were characterized by 16S rRNA PCR-DGGE using bacterial universal primers. The DGGE patterns of these soil communities were compared with noncontaminated soils found at the same TNT-destruction site. Non-polluted soils revealed complex fingerprints of microorganisms while the contaminated samples showed the presence of dominant bands, indicating that a strong selection had occurred. The biodegradation capacities of a non-polluted and a TNT-contaminated soil were evaluated by enrichment cultures with TNT as sole N-source. High and unusual denitration activities were detected with the contaminated soil under defined anaerobic conditions.