Reductive transformation of TNT by Escherichia coli resting cells: Kinetic analysis

Microbial 2,4,6-trinitrotoluene (TNT) biotransformation via sequential nitro-reduction appears a ubiquitous process, but the kinetics of these transformations have been poorly understood or described. TNT transformation by Escherichia coli was monitored and a kinetic model for reductive TNT depletion was developed and experimentally calibrated in this report. Using resting cells of aerobically pregrown E. coli, TNT was quickly reduced to hydroxylaminodinitrotoluenes. The standard Michaelis-Menten model was modified to include three additional parameters: product toxicity (T_c), substrate inhibition (K_i), and intracellular reducing power (RH) limitation. Experimentally measured product toxicity (5.2 μmol TNT/mg cellular protein) closely matched the best-fit model value (2.84 μmol TNT/mg cellular protein). Parameter identifiability and reliability (k_m, K_s, T_c, and K_i) was evaluated and confirmed through sensitivity analyses and via Monte Carlo simulations. The resulting kinetic model adequately described TNT reduction kinetics by E. coli resting cells in the absence or presence of reducing power limitation.