Browsing by Author "Naumova, R. P."

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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.
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.
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.