Browsing by Author "Ziganshin, Ayrat M."

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Aerobic degradation of 2,4,6-trinitrotoluene by the yeast strain Geotrichum candidum AN-Z4
(2010-04) Ziganshin, Ayrat M.; Gerlach, Robin; Naumenko, E. A.; Naumova, R. P.
The yeast strain Geotrichum candidum AN-Z4 isolated from an anthropogenically polluted site was able to transform 2,4,6-trinitrotoluene (TNT) via the formation of unstable intermediate hydride Meisenheimer complexes with their subsequent destruction and accumulation of nitrite and nitrate ions as the end mineral forms of nitrogen. Aeration of the medium promoted more profound destruction of this xenobiotic by the strain G. candidum AN-Z4 than static conditions. The yeast strain was shown to produce citrate, succinate, and isocitrate, which sharply acidified the medium and influenced the TNT destruction. Two possible pathways of TNT biodegradation were confirmed experimentally: (1) via the destruction of the TNT-monohydride complex (3-Hâˆ’-TNT) and (2) via the destruction of one protonated TNT-dihydride complex (3,5-2Hâˆ’-TNT Â· H+). The strain G. candidum AN-Z4, due to its ability for TNT degradation, may be promising for bioremediation of TNT-contaminated soil and water.
Effect of ferrihydrite on 2,4,6-trinitrotoluene biotransformation by an aerobic yeast
(2013-09) Khilyas, I. V.; Ziganshin, Ayrat M.; Pannier, Andy J.; Gerlach, Robin
This study investigated the impact of ferrihydrite on the pathway and rate of 2,4,6-trinitrotoluene (TNT) transformation by Yarrowia lipolytica AN-L15. The presence of ferrihydrite in the culture medium decreased the rate of TNT biotransformation but resulted in the accumulation of the same TNT metabolites as in the absence of ferrihydrite, albeit at slightly different concentrations. Transformation products observed included aromatic ring reduction products, such as hydride-Meisenheimer complexes, and nitro group reduction products, such as hydroxylamino- and amino-dinitrotoluenes. Independently of the presence of ferrihydrite the subsequent degradation of the hydride complex(es) resulted in the release of nitrite followed by its conversion to nitrate and nitric oxide at the low pH values observed during yeast cultivation. Nitric oxide generation was ascertained by electron spin resonance spectroscopy. In addition, increased Fe3+-reduction was observed in the presence of TNT and Y. lipolytica. This study demonstrates that in the presence of yeast cells, TNT hydride complexes were formed at approximately the same level as in the presence of ferrihydrite, opening up the possibility of aromatic ring cleavage, instead of promoting the production of potentially toxic nitro group reduction products in the presence of iron minerals.
Fe(III) mineral reduction followed by partial dissolution and reactive oxygen species generation during 2,4,6-trinitrotoluene transformation by the aerobic yeast Yarrowia lipolytica
(2015-02) Ziganshin, Ayrat M.; Ziganshina, Elvira E.; Byrne, James; Gerlach, Robin; Struve, Ellen; Biktagirov, Timur; Rodionov, Alexander; Kappler, Andreas
Understanding the factors that influence pollutant transformation in the presence of ferric (oxyhydr)oxides is crucial to the efficient application of different remediation strategies. In this study we determined the effect of goethite, hematite, magnetite and ferrihydrite on the transformation of 2,4,6-trinitrotoluene (TNT) by Yarrowia lipolytica AN-L15. The presence of ferric (oxyhydr)oxides led to a small decrease in the rate of TNT removal. In all cases, a significant release of NO2− from TNT and further NO2− oxidation to NO3− was observed. A fraction of the released NO2− was abiotically decomposed to NO and NO2, and then NO was likely oxidized abiotically to NO2 by O2. ESR analysis revealed the generation of superoxide in the culture medium; its further protonation at low pH resulted in the formation of hydroperoxyl radical. Presumably, a fraction of NO released during TNT degradation reacted with superoxide and formed peroxynitrite, which was further rearranged to NO3− at the acidic pH values observed in this study. A transformation and reduction of ferric (oxyhydr)oxides followed by partial dissolution (in the range of 7–86% of the initial Fe(III)) were observed in the presence of cells and TNT. Mössbauer spectroscopy showed some minor changes for goethite, magnetite and ferrihydrite samples during their incubation with Y. lipolytica and TNT. This study shows that i) reactive oxygen and nitrogen species generated during TNT transformation by Y. lipolytica participate in the abiotic conversion of TNT and ii) the presence of iron(III) minerals leads to a minor decrease in TNT transformation.
Influence of pH on 2,4,6-trinitrotoluene degradation by Yarrowia lipolytica
(2010-04) Ziganshin, Ayrat M.; Naumova, R. P.; Pannier, Andy J.; Gerlach, Robin
The microbial reduction of the aromatic ring of 2,4,6-trinitrotoluene (TNT) can lead to its complete destruction. The acid-tolerant yeast Yarrowia lipolytica AN-L15 transformed TNT through hydride ion-mediated reduction of the aromatic ring (as the main pathway), resulting in the accumulation of nitrite and nitrate ions, as well as through nitro group reduction (as minor pathway), resulting in hydroxylamino- and aminoaromatics. TNT transformation depended on the yeasts' ability to acidify the culture medium through the production of organic acids. Aeration and a low medium buffer capacity favored yeast growth and resulted in rapid acidification of the medium, which influenced the rate and extent of TNT transformation. This is the first time that nitrate has been detected as a major product of microbial TNT degradation, and this work demonstrates the importance of pH on TNT biotransformation. The ability of Y. lipolytica AN-L15 to reduce the TNT aromatic ring to form TNT-hydride complexes, followed by their denitration, makes this strain a potential candidate for bioremediation of sites contaminated with explosives. (c) 2010 Elsevier Ltd. All rights reserved.
Participation of oxygen in the bacterial transformation of 2,4,6-trinitrotoluene
(2008-04) Naumenko, E. A.; Naumov, A. V.; Suvorova, E. S.; Gerlach, Robin; Ziganshin, Ayrat M.; Lozhkin, A. P.; Silkin, N. I.; Naumova, R. P.
The exposure of Bacillus cereus ZS18 cell suspensions to 2,4,6-trinitrotoluene (TNT) in the absence of other oxidizable substrates increases oxygen uptake, exceeding the basal level of respiration of the bacterium 1.5- and 2-fold with 50 and 100 mg/liter of TNT, respectively. The interaction of both living and to less extent dead bacterial cells with TNT results in the accumulation of superoxide anion (O2-) in the extracellular medium, which was revealed by the EPR spectroscopy. The accumulation of O2- decreased by 50-70% in the presence of Cu,Zn-superoxide dismutase of animal origin. In the presence of living bacterial cells, the level of TNT decreased progressively, yielding hydroxylaminodinitrotoluenes together with O2-. In the presence of heat-killed cells, a moderate decrease in TNT was observed, and the appearance of O2- was not accompanied by the production of any detectable TNT metabolites. Chelating agents inhibited the transformation of TNT and decreased the formation of O2-. The demonstrated generation of O2- during the interaction of TNT with K4[Fe(CN)6] together with the observed effects of chelating agents suggest the participation of iron in the one-electron reduction of TNT and the functioning of an extracellular redox cycle with the involvement of molecular oxygen.
Pathways of 2,4,6-trinitrotoluene transformation by aerobic yeasts
(2013-08) Ziganshin, Ayrat M.; Gerlach, Robin
The production and use of various highly persistent synthetic compounds lead to environmental pollution. Among such compounds, 2,4,6-trinitrotoluene (TNT) is the one which is commonly used as an explosive. Synthesis and wide use of TNT in ammunition have resulted in the contamination of soil, air, surface water, and groundwater. TNT and its nitro group reduction products are highly toxic, potentially mutagenic and persistent contaminants which can persist in the environment for a long time (Spain et al. 2000; Stenuit et al. 2005; Smets et al. 2007; Singh et al. 2012). The U.S. Environmental Protection Agency has classified TNT as one of the most dangerous pollutants in the biosphere. Hence, remediation of TNT-contaminated sites is urgently warranted at places of its production and use (Keith and Telliard 1979; Fiorella and Spain 1997).Human exposure to TNT or its nitro group reduction metabolites can lead to the development of diseases, such as aplastic anemia, cataracts, impaired liver function and the formation of tumors in the urinary tract (Hathaway 1985; Yinon 1990; Leung et al. 1995). Hence, it is inevitable to work out strategies targeting the degradation of TNT.Decontamination of sites contaminated with explosives, especially with TNT, is possible with application of various physical, chemical, and biological methods. The main advantages of bioremediation are environmental friendliness and involvement of low cost (Rodgers and Bunce 2001).
Production of eight different hydride complexes and nitrite release from 2,4,6-trinitrotoluene by Yarrowia lipolytica
(2007-10) Ziganshin, Ayrat M.; Gerlach, Robin; Borch, Thomas; Naumov, A. V.; Naumova, R. P.
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.