DOI 10.1007/s00253-004-1736-x APPLIED MICROBIAL AND CELL PHYSIOLOGY

Abstract The reductive transformation of 2,4,6-trinitrotol-uene (TNT) was studied using aerobically grown Escher-ichia coli cultures. In the absence of an external carbon or energy source, E. coli resting cells transformed TNT to hydroxylaminodinitrotoluenes (2HADNT, 4HADNT, with 4HADNT as the dominant isomer), aminodinitrotoluenes (4ADNT, with sporadic detection of 2ADNT), 2,4-di (hydroxylamino)-6-nitrotoluene (24D(HA)6NT), 2,4-di-amino-6-nitrotoluene (24DA6NT), and an additional com-poundwhichwas tentatively identified as a (hydroxylamino) aminonitrotoluene isomer via gas chromatography/mass spectroscopy and spectral analysis. The resting cell assay, performed in an oxygen-free atmosphere, avoided forma-tion of azoxy dimers and provided good mass balances. Significant preference for reduction in the para versus ortho position was detected. The formation of 24D(HA) 6NT, but not ADNT, appeared inhibited by the presence of TNT. The rate and extent of TNT reduction were signif-icantly enhanced at higher cell densities, or by supplying an exogenous reducing power source, revealing the importance of enzyme concentration and reducing power. Whether the oxygen-insensitive E. coli nitroreductases, encoded by nfsA and nfsB, directly catalyze the TNT reduction or account for the complete TNT transformation pathway, remains to be determined