Bacterial degradation of the nitrobenzoic acids. 2. Reduction of the nitro group

Abstract

Growing cultures, washed cell suspensions and cell-free extracts of Nocardia species and a strain of Pseudomonas fluorescens reduce the nitrobenzoic acids to the corresponding aminobenzoic acids. Reductive dissimilation is a subsidiary process, not a primary mode of attack on the nitro group, and the aminobenzoic acids do not lie on the direct oxidative pathway of nitrobenzoic acid metabolism. Reduction of the nitro group to the amino level probably proceeds in Nocardia erythropolis via the corresponding nitroso- and hydroxylaminobenzoic acid. No separation of the enzymes responsible for the individual steps in the reductive process was obtained with standard protein-fractionation techniques. The nitroreductase is non-specific and requires reduced diphospho-pyridine nucleotide as H-donor. Its activity is stimulated by flavin-adenine dinucleotide and inhibited by hydroxylamine and nitrite. Dialysis against ethylenediaminetetra-acetic acid, 1 : 10-phenanthroline, 8-hydroxyquinoline and potassium cyanide causes extensive inhibition and reveals the requirement for a bivalent metal. Mn2+, Mg2+ and, in particular, Fe2+ ions are active. The effect of the last-named was also observed in experiments with metal-free media. The significance in the overall metabolism of several hydroxynitrobenzoic acids isolated on chromatograms from experiments with Nocardia species could not be deduced.