Biotransformation and partial mineralization of the explosive 2,4,6-trinitrotoluene (TNT) by rhizobia

Three strains, T10, B5, and M8, each belonging to a different species of th e family Rhizobiaceae and isolated from atrazine-contaminated soils, were t ested for their ability to transform 2,4,6-trinitrotoluene (TNT) (50 mug.mL (-1)) in liquid cultures using glucose as the C-source. All three strains w ere able to transform TNT to hydroxy lamino dinitro toluenes (2-HADNT, 4-HA DNT), aminodinitrotoluenes (2-ADNT, 4-ADNT), and diaminonitrotoluene (2,4-D ANT). The transformation was significantly faster in the presence of glutam ate. Furthermore, the major metabolites that accumulated in cultures were 2 -ADNT with glucose, and 4-ADNT with glutamate plus glucose. Rhizobium trifo lii T10 was also tested for its ability to transform high levels of TNT (si milar to 350 mug.mL(-1)) in a soil slurry. Almost 60% of the TNT was transf ormed within 2 days in bioaugmented soil slurries, and up to 90% when cultu res were supplemented with glucose and glutamate. However, mineralization w as minimal in all cases, less than 2% in 78 days. This is the first report on the degradation of TNT by rhizobial strains, and our findings suggest th at rhizobia have the potential to play an important role in the safe decont amination of soils and sites contaminated with TNT if bioaugmentation with rhizobia is shown to have no ecotoxicological consequence.