Purification and characterization of nitroreductase from red alkaliphilic bacterium Aquiflexum sp. DL6

Nitroaromatic compounds are toxic to living organisms. Most of them exhibit human mutagenic and carcinogenic potential. Biotransformation and bioremediation processes can convert these compounds into non-toxic compounds. Acclimatization of bacterial strain Aquiflexum sp. DL6 with nitro-aromatics resulted in significant induction of nitroreductase (EC 1.5.1.34). The enzyme was purified by the combination of DEAE-cellulose and Sephadex G-100 column chromatography with 80-fold purification and 22% yield. Molecular weight of purified nitroreductase was estimated to be 29 kDa by SDS-PAGE. The enzyme characteristics were explored by varying the pH and temperatures, and the optimum activity was found at pH 9.5 and 40°C. It was revealed that the substrate specificity of nitroreductase of Aquiflexum sp. DL6 was wide for the most of the tested nitro-aromatic compounds. The kinetic parameters like Michaelis constant and velocity maxima were determined with o-nitrophenol and NADH as substrates.