Biodegradation of 2,4,6-trinitrotoluene by Citrobacter sp. YC4 and its potential effects in ecotoxicology

The compound 2,4,6-trinitrotoluene (TNT) is a secondary explosive widely used for both military and civil purposes around the world.  As a result, residual TNT has been detected as an environmental pollutant both in soil and groundwater. TNT is highly toxic and carcinogenic; therefore, the control and remediation of TNT contamination is a critical environmental issue.  A bacterium able to utilize TNT as sole source of nitrogen but not sole source of carbon was isolated from soil contaminated with TNT.  The initial identification of this bacterium determined by 16S rRNA gene analysis suggested that the isolate belongs to the genus Citrobacter and was designed as strain YC4.  When grown in medium containing TNT as sole nitrogen source, the concentration of TNT decreased by more than 80% after 48 h as determined by HPLC.  Additionally, resting cells of Citrobacter sp. YC4 grown in the medium with TNT as sole nitrogen source was able to  rapidly transform (metabolize) TNT, in constrast to cells grown in LB medium.  Cytotoxicity of TNT and its metabolites produced by biodegradation by Citrobacter sp. YC4 determined by using WST-1-based cell cytotoxicity assay is also discussed.