Denitration of 2,4,6-trinitrotoluene in aqueous solutions using small-molecular-weight catalyst(s) secreted by Pseudomonas aeruginosa ESA-5

Biogenic Fenton-like Reaction Involvement in Cometabolic Degradation of Tetrabromobisphenol A by Pseudomonas sp. fz

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant (BFR) that has frequently been detected in various environmental compartments. Although TBBPA biotransformation has been observed under both aerobic and anaerobic conditions, knowledge of the detailed mechanism of direct aerobic TBBPA biodegradation still remains limited. In this study, the underlying mechanism of cometabolic degradation of TBBPA by Pseudomonas sp. fz under aerobic conditions was investigated. Two key degradation pathways (beta scission and debromination) were proposed based on triple quadrupole liquid chromatography-mass spectrometry (LC-MS) analysis. TBBPA degradation by strain fz was demonstrated to be an extracellular process associated with the low-molecular-mass component (LMMC). Moreover, LMMC was preliminarily identified as oligopeptides, mainly consisting of glycine, proline, and alanine in a 2:1:1 molar ratio. Quenching studies suggested the involvement of hydroxyl radicals ((•)OH) in extracellular TBBPA degradation. To the best of our knowledge, we provide the first evidence that TBBPA was degraded by a biogenic Fenton-like reaction mediated via extracellular H2O2 and Fe(II)-oligopeptide complexes by the genus Pseudomonas. This study provides a new insight into the fate and biodegradation of TBBPA and other organic pollutants in natural and artificial bioremediation environments.

Improved TNT detoxification by starch addition in a nitrogen-fixing Methylophilus-dominant aerobic microbial consortium

In this study, a novel aerobic microbial consortium for the complete detoxification of 2,4,6-trinitrotoluene (TNT) was developed using starch as a slow-releasing carbon source under nitrogen-fixing conditions. Aerobic TNT biodegradation coupled with microbial growth was effectively stimulated by the co-addition of starch and TNT under nitrogen-fixing conditions. The addition of starch with TNT led to TNT mineralization via ring cleavage without accumulation of any toxic by-products, indicating improved TNT detoxification by the co-addition of starch and TNT. Pyrosequencing targeting the bacterial 16S rRNA gene suggested that Methylophilus and Pseudoxanthomonas population were significantly stimulated by the co-addition of starch and TNT and that the Methylophilus population became predominant in the consortium. Together with our previous study regarding starch-stimulated RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) degradation (Khan et al., J. Hazard. Mater. 287 (2015) 243-251), this work suggests that the co-addition of starch with a target explosive is an effective way to stimulate aerobic explosive degradation under nitrogen-fixing conditions for enhancing explosive detoxification.

Aerobic denitration of 2,4,6-trinitrotoluene in the presence of phenazine compounds and reduced pyridine nucleotides

Phenazine-containing spent culture supernatants of Pseudomonas aeruginosa concentrated with a C18 solid-phase extraction cartridge initiate NAD(P)H-dependent denitration of 2,4,6-trinitrotoluene (TNT). In this study, TNT denitration was investigated under aerobic conditions using two phenazine secondary metabolites excreted by P. aeruginosa, pyocyanin (Py) and its precursor phenazine-1- carboxylic acid (PCA), and two chemically synthesized pyocyanin analogs, phenazine methosulfate (PMS+) and phenazine ethosulfate (PES+). The biomimetic Py/NAD(P)H/O2 system was characterized and found to extensively denitrate TNT in unbuffered aqueous solution with minor production of toxic amino aromatic derivatives. To a much lesser extent, TNT denitration was also observed with PMS+ and PES+ in the presence of NAD(P)H. No TNT denitration was detected with the biomimetic PCA/NAD(P)H/O2 system. Electron paramagnetic resonance (EPR) spectroscopy analysis of the biomimetic Py/NAD(P)H/O2 system revealed the generation of superoxide radical anions (O2 •−). In vitro TNT degradation experiments in the presence of specific inhibitors of reactive oxygen species suggest a nucleophilic attack of superoxide radical anion followed by TNT denitration through an as yet unknown mechanism. The results of this research confirm the high functional versatility of the redox-active metabolite pyocyanin and the susceptibility of aromatic compounds bearing electron withdrawing substituents, such as nitro groups, to superoxide-driven nucleophilic attack.

Soils contaminated with explosives: Environmental fate and evaluation of state-of-the-art remediation processes (IUPAC Technical Report)

An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, from the products of a chemical reaction involving explosive materials, or from a nuclear reaction that is uncontrolled. In order for an explosion to occur, there must be a local accumulation of energy at the site of the explosion, which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. Modern explosives or energetic materials are nitrogen-containing organic compounds with the potential for self-oxidation to small gaseous molecules (N2, H2O, and CO2). Explosives are classified as primary or secondary based on their susceptibility of initiation. Primary explosives are highly susceptible to initiation and are often used to ignite secondary explosives, such as TNT (2,4,6-trinitrotoluene), RDX (1,3,5-trinitroperhydro-1,3,5-triazine), HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane), and tetryl (N-methyl-N-2,4,6-tetranitro-aniline).