Pathways for Degrading TNT by Thu-Z: a Pantoea sp Strain

2,4,6-Trinitrotoluene (TNT), an extensively used and versatile explosive, is harmful in soil and water. In the present study, four bacterial strains capable of degrading TNT have been isolated from contaminated sites and named as Thu-A, Thu-B, Thu-C, and Thu-Z. Thu-Z, which gave the highest degradation efficiency compared to the others, was assigned to the genus Pantoea according to its 16S rRNA gene. Similarities in both biochemical properties and morphology suggested that Thu-Z was a Pantoea sp. strain. Thu-Z was proved to be capable of using TNT as a sole nitrogen source by cleaving NO2 from the nitroaromatic ring by direct aromatic ring reduction. Under nitrogen-limited conditions, 96.6 % N of TNT was consumed by Thu-Z for growth, which was determined in terms of NaNO2. Trace nitro reduction metabolites such as 2,4-diamino-6-nitrotoluene (24Dam) and 2,6-diamino-4-nitrotoluene (26Dam) were identified in the presence of (NH4)(2)SO4. On the other hand, 4,4',6,6'-tetranitro-2,2'-azoxytoluene (22Azo) and 2,2',6,6'-tetranitro-4,4'-azoxytoluene (44Azo) were detected in the absence of (NH4)(2)SO4. These indicated the existence of a dual pathway for Thu-Z, while the direct aromatic ring reduction was predominant. Addition of a nitrogen source ((NH4)(2)SO4) after inoculation stimulated the growth of Thu-Z and accelerated TNT degradation.