Biodegradation and physiological response mechanism of a bacterial strain to 2,4,6-trinitrotoluene contamination

The aim of this study was to reveal the biodegradation characteristics and physiological response mechanism of a newly isolated bacterium to 2,4,6-trinitrotoluene (TNT) contamination. A Klebsiella variicola strain with high efficiency of TNT degradation was used as the test strain to analyze the changes in cell growth, morphology, and functional groups under different TNT concentrations (0, 100 mg⋅L^-1) and the effects of TNT stress on the metabolic profile as revealed by non-targeted metabonomics. A TNT concentration of 100 mg L^-1 caused a significant increase in the 5-day biochemical oxygen demand (BOD₅) to 950 mg L^-1, while the degradation rate of TNT reached 100% within 30 h after inoculation with Klebsiella variicola. Fourier transform infrared spectroscopy (FTIR) analysis showed changes in the characteristic peak of triamide by TNT treatment. Non-targeted metabonomics identified a total of 544 differentially produced metabolites under TNT treatment (252 upregulated and 292 downregulated), mainly lipids and lipid-like molecules. The metabolic pathways associated with amino acid biosynthesis and metabolism were the most significantly enriched pathways, and simultaneous detection showed that TNT was degraded to 4-amino-2,6-dinitrotoluene (DNT), 2-hydroxylamino-4,6-DNT, 2-amino-4,6-DNT, 2-amino-4-nitrotoluene, and 2,4-DNT. These results confirmed that Klebsiella variicola has a high tolerance to TNT and efficiently degrades it. The degradation mechanism involves TNT-induced accelerated amino acid biosynthesis, production of a protease to catalyze the TNT transformation, and the participation of the transformed TNT products in cell metabolism.