Rapid spectrophotometric determination of 2,4,6-trinitrotoluene in a Pseudomonas enzyme assay

Persistent organic pollutants in water resources: Fate, occurrence, characterization and risk analysis

Persistent organic pollutants (POPs) are organic chemicals that can persist in the environment for a longer period due to their non-biodegradability. The pervasive and bio-accumulative behavior of POPs makes them highly toxic to the environmental species including plants, animals, and humans. The present review specifies the POP along with their fate, persistence, occurrence, and risk analysis towards humans. The different biological POPs degradation methods, especially the microbial degradation using bacteria, fungi, algae, and actinomycetes, and their mechanisms were described. Moreover, the source, transport of POPs to the environmental sources, and the toxic nature of POPs were discussed in detail. Agricultural and industrial activities are distinguished as the primary source of these toxic compounds, which are delivered to air, soil, and water, affecting on the social and economic advancement of society at a worldwide scale. This review also demonstrated the microbial degradation of POPs and outlines the potential for an eco-accommodating and cost-effective approach for the biological remediation of POPs using microbes. The direction for future research in eliminating POPs from the environmental sources through various microbial processes was emphasized.

Biotransformation of 2,4,6-Trinitrotoluene by Pseudomonas sp. TNT3 isolated from Deception Island, Antarctica

2,4,6-Trinitrotoluene (TNT) is a nitroaromatic explosive, highly toxic and mutagenic for organisms. In this study, we report for the first time the screening and isolation of TNT-degrading bacteria from Antarctic environmental samples with potential use as bioremediation agents. Ten TNT-degrading bacterial strains were isolated from Deception Island. Among them, Pseudomonas sp. TNT3 was selected as the best candidate since it showed the highest tolerance, growth, and TNT biotransformation capabilities. Our results showed that TNT biotransformation involves the reduction of the nitro groups. Additionally, Pseudomonas sp. TNT3 was capable of transforming 100 mg/L TNT within 48 h at 28 °C, showing higher biotransformation capability than Pseudomonas putida KT2440, a known TNT-degrading bacterium. Functional annotation of Pseudomonas sp. TNT3 genome revealed a versatile set of molecular functions involved in xenobiotic degradation pathways. Two putative xenobiotic reductases (XenA_TNT3 and XenB_TNT3) were identified by means of homology searches and phylogenetic relationships. These enzymes were also characterized at molecular level using homology modelling and molecular dynamics simulations. Both enzymes share different levels of sequence similarity with other previously described TNT-degrading enzymes and with their closest potential homologues in databases.

Application of Arthrospira (Spirulina) platensis against Chemical Pollution of Water

The basis of phytoremediation technology for cleaning chemically polluted water was developed in the framework of the presented work. This technology is based on the ability of blue-green alga Arthrospira platensis to eliminate different environmental toxicants from water. This technological approach was conducted for the following pollutants: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), 2,4,6-trinitrotoluene (TNT), and cesium ions. The effectiveness of the technology was tested in model experiments, which were carried out in glass containers (volume 40 L). In particular, the different concentrations of alga biomass with the aforementioned pollutants were incubated with permanent illumination conditions and air barbotage, at a temperature of 25 °C. The results of the model experiments showed that after two weeks from the start of remediation Arthrospira effectively cleaned artificially polluted waters. Particularly in the case of TNT 56 mg/L concentration, the effect of water remediation was 97%. In the case of DDT 10 mg/L concentration, the degree of cleaning was 90%. Similar results were obtained in the case of 100 mg/L concentration of cesium ions. Thus, the model experiments confirmed that the alga Arthrospira effectively removed tested pollutants from water. That is the basis of phytoremediation technology.

Fungal elimination of 2,4,6-trinitrotoluene (TNT) from the soils

The analysis of microscopic fungi collection created at theDurmishidze Institute of Biochemistry and Biotechnology revealed 107 strains assimilating 2,4,6-TNT (2,4,6-trinitrotoluene) belonging to the different fungal genera. The strains have been isolated from the polluted areas adjacent to the military grounds and industrial waste waters. It has been shown TNT is degraded most actively by strains belonging to the following genera: Trichoderma, Aspergillus, Mucor and Trichoderma. Optimal cultivation conditions for highly active strains -the destructors of TNT have been revealed. It has been established that the carbon skeleton of TNT being utilized by the mentioned strains undergoes biotransformation. The existence of radioactive intermediates of biotransformation, organic acids (70-90%) and amino acids (10-30%) have been detected in liquid culture. Radioactive label of 1-14C-TNT is mostly found in fumaric acid, which is known as one of the main products of benzene biotransformation and further conversion into succinic acid. Remediation level of TNT-contaminated red and black soils treated by the most active strains Aspergillus nigerN2-2 and Mucor sp. T1-1 have been studied under laboratory and field conditions. Cultivation of the above mentioned strains under laboratory conditions in sterile, black and red soils for 30 days at 30°C allowed decreasing the content of TNT in black soil to the residual, and in red soil - to 15%; cultivation of Aspergillus niger N2-2 decreased the amount of TNT in black soil to 11 and in red soil - to 21%. Under field conditions, TNT degradation level in contaminated soils by naturally existing micro flora during 100 days was equal to 40-50%, and in the case of additional introduction of both fungal strains, TNT-destructors reached 80%.

Sensors--an effective approach for the detection of explosives

The detection of explosives and explosive related illicit materials is an important area for preventing terrorist activities and for putting a check on their deleterious effects on health. A number of different methods, based on different principles, have been developed in the past for the detection of explosives. Sensors are one of those methods of detection which have capability to mimic the canine system and which are known to be the most reliable method of detection. The objective of this review is to provide comprehensive knowledge and information on the sensors operating on different transduction principles, ranging from electrochemical to immunosensors, being used for the detection of explosives as they pose a threat for both health and security of the nation. The review focuses mainly on the sensors developed in the recent 5 years and is prepared through summary of literature available on the subject.

Absorbance change and static quenching of fluorescence of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) by trinitrotoluene (TNT)

Meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) interacts with trinitrotoluene (TNT) and forms a 1:1 complex with a new absorbance peak at 422 nm. TNT quenches TPPS emission intensity at 645 and 702 nm when excited at 413 nm. The TPPS-TNT complex is formed in the ground state on the basis of a linear Stern-Volmer plot indicative of static quenching. The association constants determined from absorbance and fluorescence studies are in excellent agreement.

Transformation of 2,4,6-trinitrotoluene (TNT) by Raoultella terrigena

Manufacture of nitroorganic explosives generates toxic wastes leading to contamination of soils and waters, especially groundwater. For that reason bacteria living in environments highly contaminated with 2,4,6-trinitrotoluene (TNT) and other nitroorganic compounds were investigated for their capacity for TNT degradation. One isolate, Raoultella terrigena strain HB, removed TNT at concentrations between 10 and 100 mg l(-1) completely from culture supernatants under optimum aerobic conditions within several hours. Only low concentrations of nutrient supplements were needed for the cometabolic transformation process. Radioactivity measurements with ring-labelled (14)C-TNT detected about 10-20% of the initial radioactivity in the culture supernatant and the residual 80-90% as water-insoluble organic compounds in the cellular pellet. HPLC analysis identified aminodinitrotoluenes (2-ADNT, 4-ADNT) and diaminonitrotoluenes (2,4-DANT) as the metabolites which remained soluble in the culture medium and azoxy-dimers as the main products in the cell extracts. Hence, the new isolate could be useful for the removal of TNT from contaminated waters.

Absorption, distribution, and transformation of TNT in higher plants

The ability of eight species of plants to assimilate 2,4,6-trinitrotoluene (TNT) was investigated. Glycine max (soybean), in particular, demonstrated rapid assimilation of high concentrations of this explosive. Penetration and localization of [1-(14)C]-TNT in plant root cells and leaves were studied via electron microscopic autoradiography. TNT was shown to be localized primarily on membrane structures involved in the transportation of nicotinamide coenzymes (membranes of endoplasmic reticulum, mitochondria, plastids). [1-(14)C]-TNT in roots was incorporated mainly in low-molecular-weight metabolites; however, in stems and leaves, the radiocarbon was incorporated in biopolymers. Enzymatic transformation of TNT in roots was studied, and it was found that degradation involved mainly nitroreductase acting on the TNT nitro groups. The process was intensified in the presence of electron donors--NADH and NADPH. Nitroreductase activity was revealed in root cell cytosol and expression was strongly induced by plant cultivation on TNT-containing media. Oxidation of [C(3)H(3)]TNT by peroxidase and phenoloxidase was also studied. In contrast to the strongly induced nitroreductase, levels of these enzymes changed very little with TNT addition. This suggests that the main pathway of TNT transformation in plant cells is nitro group reduction. A plant's nitroreductase activity and its ability to incorporate TNT from aqueous solutions were correlated in four plants that were studied. The results suggest that plant nitroreductase activity may serve as a good biochemical indicator of plants that can be used for phytoremediation of soils contaminated with TNT.

Crucial problem in rapid spectrophotometric determination of 2,4,6-trinitrotoluene and its breakthrough method

A rapid spectrophotometric determination for 2,4,6-trinitrotoluene (TNT) is significant because this method is suitable for simultaneous analyses of the numerous samples. We found one problem that TNT reduction products interfere with the TNT detection in this assay, and we overcame this problem by heating the samples at 95 degrees C, resulting in the production of compounds that did not interfere.

Optimisation of a microbial bioassay for contaminated soil monitoring: bacterial inoculum standardisation and comparison with Microtox assay

This work represents the first step to set up a toxicity testing procedure and to evaluate the sensitivity of the test microorganism to several classes of environmental pollutants. First, three different techniques were employed to standardise the microbial inoculum, then two different toxicity assessment protocols have been compared: Microtox and a dehydrogenase (DHase) activity inhibition test. The main goal was the optimisation of a microbial bioassay based on the dehydrogenase activity (DHase) inhibition in Pseudomonas fluorescens bacterial strain ATCC 13525. Triphenyl tetrazolium chloride (TTC) was used as electron acceptor and its reduction produces Triphenyl formazane (TPF). The P. fluorescens DHase inhibition bioassay was investigated for being a reliable and rapid method for assessing toxicity. The optimisation of the operating conditions resulted in a repeatable bioassay. Then, P. fluorescens and Vibrio fischeri sensitivity were firstly compared by testing Zn++, one of the reference compounds for Microtox test. In addition, other compounds (Ni++, Cd++, Cu++, phenol) were also tested with both bioassays. A high statistical significance of data was obtained with the logistic curve. The present work has demonstrated that P. fluorescens is as sensitive as Microtox culture (V. fischeri), for some of the metal ions. With reference to organic compounds, the lower sensitivity of P. fluorescens to phenol makes its use difficult in organic polluted samples.

Vibrio harveyi nitroreductase is also a chromate reductase

The chromate reductase purified from Pseudomonas ambigua was found to be homologous with several nitroreductases. Escherichia coli DH5alpha and Vibrio harveyi KCTC 2720 nitroreductases were chosen for the present study, and their chromate-reducing activities were determined. A fusion between glutathione S-transferase (GST) and E. coli DH5alpha NfsA (GST-EcNfsA), a fusion between GST and E. coli DH5alpha NfsB (GST-EcNfsB), and a fusion between GST and V. harveyi KCTC 2720 NfsA (GST-VhNfsA) were prepared for their overproduction and easy purification. GST-EcNfsA, GST-EcNFsB, and GST-VhNFsA efficiently reduced nitrofurazone and 2,4,6-trinitrotoluene (TNT) as their nitro substrates. The K(m) values for GST-EcNfsA, GST-EcNfsB, and GST-VhNfsA for chromate reduction were 11.8, 23.5, and 5.4 micro M, respectively. The V(max) values for GST-EcNfsA, GST-EcNfsB, and GST-VhNfsA were 3.8, 3.9, and 10.7 nmol/min/mg of protein, respectively. GST-VhNfsA was the most effective of the three chromate reductases, as determined by each V(max)/K(m) value. The optimal temperatures of GST-EcNfsA, GST-EcNfsB, and GST-VhNfsA for chromate reduction were 55, 30, and 30 degrees C, respectively. Thus, it is confirmed that nitroreductase can also act as a chromate reductase. Nitroreductases may be used in chromate remediation. GST-EcNfsA, GST-EcNfsB, and GST-VhNfsA have a molecular mass of 50 kDa and exist as a monomer in solution. Thin-layer chromatography showed that GST-EcNfsA, GST-EcNfsB, and GST-VhNfsA contain FMN as a cofactor. GST-VhNfsA reduced Cr(VI) to Cr(III). Cr(III) was much less toxic to E. coli than Cr(VI).