Models of 2,4,6-trinitrotoluene (TNT) initial conversion by yeasts

Investigating the Potential of Fusarium solani and Phanerochaete chrysosporium in the Removal of 2,4,6-TNT

Past and  recent applications of 2,4,6-trinitrotoluene (TNT) in military and civilian industries have led to contamination of soil and marine ecosystems. Among various TNT remediation techniques, biological remediation is widely accepted for its sustainability, low cost, and scalable applications. This study was designed to isolate a fungus strain from a TNT-contaminated soil to investigate its tolerance to and potential for removal of TNT. Thus, a soil column with a history of periodic TNT amendment was used to isolate dominant strains of fungi Fusarium solani isolate, which is not commonly reported for TNT mineralization and was found predominant in the subsurface layer of the TNT-amended soil. F. solani was investigated for TNT concentration tolerance at 30, 70, and 100 mg/L on agar plates and for TNT removal in liquid cultures at the same given concentrations. F. solani activity was compared with that of a reference soil-born fungus that has been intensively studied for TNT removal (Phanerochaete chrysosporium) obtained from the American Type Culture Collection. On agar media, F. solani showed a larger colony diameter than P. chrysosporium at similar TNT concentrations, indicating its high potential to tolerate toxic levels of TNT as found in contaminated sites. In the liquid culture medium, F. solani was able to significantly produce higher biomass than P. chrysosporium in all TNT concentrations. The TNT removal percentage from the liquid culture at the highest TNT concentration of 100 mg/L reached about 85% with F. solani, while P. chrysosporium was no better than 25% at the end of an 84-h incubation period. Results indicate a significant potential of using F. solani in the bioremediation of polluted TNT soils that overcome the high concentration barrier in the field. However, further investigation is needed to identify enzymatic potential and the most effective applications and possible limitations of this method on a large scale.

DNA adduct formation in Saccharomyces cerevisiae following exposure to environmental pollutants, as in vivo model for molecular toxicity studies

DNA adduction in the model yeast Saccharomyces cerevisiae was investigated after exposure to the fungicide penconazole and the reference genotoxic compound benzo(a)pyrene, for validating yeasts as a tool for molecular toxicity studies, particularly of environmental pollution. The effect of the toxicants on the yeast's growth kinetics was determined as an indicator of cytotoxicity. Fermentative cultures of S. cerevisiae were exposed to 2 ppm of Penconazole during different phases of growth; while 0.2 and 2 ppm of benzo(a)pyrene were applied to the culture medium before inoculation and on exponential cultures. Exponential respiratory cultures were also exposed to 0.2 ppm of B(a)P for comparison of both metabolisms. Penconazole induced DNA adducts formation in the exponential phase test; DNA adducts showed a peak of 54.93 adducts/109 nucleotides. Benzo(a)pyrene induced the formation of DNA adducts in all the tests carried out; the highest amount of 46.7 adducts/109 nucleotides was obtained in the fermentative cultures after the exponential phase exposure to 0.2 ppm; whereas in the respiratory cultures, 14.6 adducts/109 nucleotides were detected. No cytotoxicity was obtained in any experiment. Our study showed that yeast could be used to analyse DNA adducts as biomarkers of exposure to environmental toxicants.

Extremophilic yeasts: the toughest yeasts around?

Microorganisms are widely distributed in a multitude of environments including ecosystems that show challenging features to most life forms. The combination of extreme physical and chemical factors contributes to the definition of extreme habitats although the definition of extreme environments changes depending on one's point of view: anthropocentric, microbial-centric or zymo-centric. Microorganisms that live under conditions that cause hard survival are called extremophiles. In particular organisms that require extreme conditions are called true extremophiles while organisms that tolerate them to some extent are termed extremotolerant. Deviation of temperature, pH, osmotic stress, pressure and radiation from the common range delineates extreme environments. Yeasts are versatile eukaryotic organisms that are not frequently considered the toughest microorganisms in comparison with prokaryotes. Nevertheless extremophilic or extremotolerant species are present also within this group. Here a brief description is provided of the main extreme habitats and the metabolic and physiological modifications adopted by yeasts depending on their adverse conditions. Additionally the main extremophilic and extremotolerant yeast species associated with a few extreme habitats are listed.

Genetically engineered microorganisms for the detection of explosives' residues

The manufacture and use of explosives throughout the past century has resulted in the extensive pollution of soils and groundwater, and the widespread interment of landmines imposes a major humanitarian risk and prevents civil development of large areas. As most current landmine detection technologies require actual presence at the surveyed areas, thus posing a significant risk to personnel, diverse research efforts are aimed at the development of remote detection solutions. One possible means proposed to fulfill this objective is the use of microbial bioreporters: genetically engineered microorganisms “tailored” to generate an optical signal in the presence of explosives’ vapors. The use of such sensor bacteria will allow to pinpoint the locations of explosive devices in a minefield. While no study has yet resulted in a commercially operational system, significant progress has been made in the design and construction of explosives-sensing bacterial strains. In this article we review the attempts to construct microbial bioreporters for the detection of explosives, and analyze the steps that need to be undertaken for this strategy to be applicable for landmine detection.

Ecotoxicological evaluation of wastewater from 2.4.6-TNT production

During the manufacture of explosives, large amounts of water are used to remove unwanted by-products generated. This water in turn, ends up in wastewater treatment plants or water bodies. The aim of this study was to evaluate the toxic potential of effluent generated by 2.4.6-Trinitrotoluene (TNT) production, yellow water, red water and mixture of yellow and red water, produced from a plant located in the Paraíba Valley, São Paolo state, Brazil. Daphnia similis, Danio rerio, Escherichia coli, Pseudomonas putida and Pseudokircheneriella subcaptata were used as test organisms. Physicochemical parameters such as color, pH, conductivity, total dissolved solids, dissolved oxygen, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were evaluated. Effluent from 2.4.6-TNT production was extremely toxic to all test organisms. The physicochemical parameters evaluated showed high levels of conductivity (from 41.533 to 42.344 μS /cm) and chemical oxygen demand (COD of 8471 to 27.364 mg/L) for the effluents analyzed.

Production of eight different hydride complexes and nitrite release from 2,4,6-trinitrotoluene by Yarrowia lipolytica

2,4,6-Trinitrotoluene (TNT) transformation by the yeast strain Yarrowia lipolytica AN-L15 was shown to occur via two different pathways. Direct aromatic ring reduction was the predominant mechanism of TNT transformation, while nitro group reduction was observed to be a minor pathway. Although growth of Y. lipolytica AN-L15 was inhibited initially in the presence of TNT, TNT transformation was observed, indicating that the enzymes necessary for TNT reduction were present initially. Aromatic ring reduction resulted in the transient accumulation of eight different TNT-hydride complexes, which were characterized using high-performance liquid chromatography, UV-visible diode array detection, and negative-mode atmospheric pressure chemical ionization mass spectrometry (APCI-MS). APCI-MS analysis revealed three different groups of TNT-hydride complexes with molecular ions at m/z 227, 228, and 230, which correspond to TNT-mono- and dihydride complexes and protonated dihydride isomers, respectively. One of the three protonated dihydride complex isomers detected appears to release nitrite in the presence of strain AN-L15. This release of nitrite is of particular interest since it can provide a pathway towards complete degradation and detoxification of TNT.

TNT biotransformation: when chemistry confronts mineralization

Our understanding of the genetics and biochemistry of microbial 2,4,6-trinitrotoluene (TNT) biotransformation has advanced significantly during the past 10 years, and biotreatment technologies have developed. In this review, we summarize this new knowledge. A number of enzyme classes involved in TNT biotransformation include the type I nitroreductases, the old yellow enzyme family, a respiration-associated nitroreductase, and possibly ring hydroxylating dioxygenases. Several strains harbor dual pathways: nitroreduction (reduction of the nitro group in TNT to a hydroxylamino and/or amino group) and denitration (reduction of the aromatic ring of TNT to Meisenheimer complexes with nitrite release). TNT can serve as a nitrogen source for some strains, and the postulated mechanism involves ammonia release from hydroxylamino intermediates. Field biotreatment technologies indicate that both stimulation of microbial nitroreduction and phytoremediation result in significant and permanent immobilization of TNT via its metabolites. While the possibility for TNT mineralization was rekindled with the discovery of TNT denitration and oxygenolytic and respiration-associated pathways, further characterization of responsible enzymes and their reaction mechanisms are required.

Assessment of 4-nitro-1,8-naphthalic anhydride reductase activity in homogenates of bakers’ yeast by reversed-phase high-performance liquid chromatography

A simple reversed-phase high-performance liquid chromatographic (RP-HPLC) method was developed for the simultaneous determination of yield and conversion ratio of 4-nitro-1,8-naphthalic anhydride to 4-amino-1,8-naphthalic anhydride following incubation with a crude bakers' yeast homogenate. The analytes were separated on a C18 column in gradient mode. The detection limit of 4-amino-1,8-naphthalic anhydride is 10ng/microl when using a 10microl sample injection volume. The nitroreductase activity in the homogenate system can be assessed during the bioconversion process. The method can be used for the simultaneous detection of 4-hydroxylamino-1,8-naphthalic anhydride, an intermediate with limited stability.

2,4,6-trinitrotoluene transformation by a tropical marine yeast, Yarrowia lipolytica NCIM 3589

Yarrowia lipolytica NCIM 3589, a tropical marine degrader of hydrocarbons and triglycerides transformed 2,4,6-trinitrotoluene (TNT) very efficiently. Though this yeast could not utilize TNT as the sole carbon or nitrogen source, it was capable of reducing the nitro groups in TNT to aminodinitrotoluene (ADNT). In a complete medium containing glucose and ammonium sulphate as the available carbon and nitrogen sources respectively, the culture was able to completely transform 1 mM (227 ppm) of TNT under such conditions. A dual pathway was found to be functional, one of which resulted in the formation of the hydride-Meisenheimer complex (H(-)TNT) as a transiently accumulating metabolite that was subsequently denitrated to 2,4-dinitrotoluene (2,4-DNT), whereas the other pathway resulted in the formation of amino derivatives. The presence of increasing amounts of reducing equivalents in the form of glucose promoted better growth and the nitroreductases of this yeast to reduce the aromatic ring to 2,4-DNT although, the reduction of the nitro groups to amino groups was the major functional pathway. The ability of this tropical marine yeast to transform TNT into products such as 2,4-DNT which in turn could be metabolized by other microbes has implications in the use of this yeast for bioremediation of TNT polluted marine environments.