Formation of hydride-Meisenheimer complexes of picric acid (2,4,6- trinitrophenol) and 2,4-dinitrophenol during mineralization of picric acid by Nocardioides sp. strain CB 22-2

Abstract

There are only a few examples of microbial conversion of picric acid (2,4,6-trinitrophenol). None of the organisms that have been described previously is able to use this compound as a sole source of carbon, nitrogen, and energy at high rates. In this study we isolated and characterized a strain, strain CB 22-2, that was able to use picric acid as a sole source of carbon and energy at concentrations up to 40 mM and at rates of 1.6 mmol · h-1 · g (dry weight) of cells-1 in continuous cultures and 920 μmol · h-1 · g (dry weight) of cells-1 in flasks. In addition, this strain was able to use picric acid as a sole source of nitrogen at comparable rates in a nitrogen-free medium. Biochemical characterization and 16S ribosomal DNA analysis revealed that strain CB 22-2 is a Nocardioides sp. strain. High- pressure liquid chromatography and UV-visible light data, the low residual chemical oxygen demand, and the stoichiometric release of 2.9 ± 0.1 mol of nitrite per mol of picric acid provided strong evidence that complete mineralization of picric acid occurred. During transformation, the metabolites detected in the culture supernatant were the [H-]-Meisenheimer complexes of picric acid and 2,4-dinitrophenol (H--DNP), as well as 2,4- dinitrophenol. Experiments performed with crude extracts revealed that H-- DNP formation indeed is a physiologically relevant step in picric acid metabolism.