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    Individual and combined inhibitory effects of methanol and toluene on acetyl-CoA synthetase expression level of acetoclastic methanogen, Methanosaeta concilii
    (Elsevier Sci Ltd, 2015) Akyol, Cagri; Ince, Orhan; Coban, Halil; Koksel, Gozde; Cetecioglu, Zeynep; Oz, Nilgun Ayman; Ince, Bahar
    Organic solvents found in waste streams can be inhibitory to microbial communities in wastewater treatment plants. In this study, possible inhibitory effects of commonly used organic solvents, methanol and toluene, were investigated in batch anaerobic digestion tests. Anaerobic sludges were fed with acetate repeatedly and exposed to various concentrations of toluene, methanol and mixture of them. Expression level of the key enzyme of acetoclastic methanogenesis, acetyl-CoA synthetase 1 (Acs1), was determined by reverse transcriptase real time PCR. Additionally, active populations of Methanosaeta spp. were monitored and quantified by fluorescent in situ hybridization (FISH). Transcript abundance of Acs1 was 1.31 x 10(6) mRNAs ml(-1) in the control reactors; whereas, singular methanol exposure of 0.1 M, 0.3 M, 0.5 M and 1.0 M and methanol + toluene combination of 1.0 M + 0.5 mM and 1.0 M + 1.5 mM did not cause any significant effect on the acetyl-CoA expression level. However, singular toluene-exposed serum bottle reactors were completely inhibited after 3rd exposure at all concentrations from 0.5 mM to 4.0 mM. FISH results for singular methanol and toluene additions as well as their combination in the ranges studied showed no particular effect on the relative abundance of Methanosaeta spp. cells. (C) 2015 Elsevier Ltd. All rights reserved.
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    Inhibition effect of isopropanol on acetyl-CoA synthetase expression level of acetoclastic methanogen, Methanosaeta concilii
    (Elsevier Science Bv, 2011) Ince, Bahar; Koksel, Gozde; Cetecioglu, Zeynep; Oz, Nilgun Ayman; Coban, Halil; Ince, Orhan
    Isopropanol is a widely found solvent in industrial wastewaters, which have commonly been treated using anaerobic systems. In this study, inhibitory effect of isopropanol on the key microbial group in anaerobic bioreactors, acetoclastic methanogens, was investigated. Anaerobic sludges in serum bottles were repeatedly fed with acetate and isopropanol; and quantitative real-time PCR was used for determining effect of isopropanol on the expression level of a key enzyme in acetoclastic methane production, acetyl-CoA synthetase of Methanosaeta concilii. Active Methanosaeta spp. cells were also quantified using Fluorescent in situ hybridization (FISH). Transcript abundance of acetyl-CoA synthetase was 1.23 +/- 0.62 x 10(6) mRNAs/mL in the uninhibited reactors with 222 mL cumulative methane production. First exposure to isopropanol resulted in 71.2%, 84.7%, 89.2% and 94.6% decrease in mRNA level and 35.0%, 65.0%, 91.5% and 100.0% reduction in methane production for isopropanol concentrations of 0.1 M, 0.5 M, 1.0 M and 2.0 M, respectively. Repeated exposures resulted in higher inhibitions; and at the end of test, fluorescent intensities of active Methanosaeta cells were significantly decreased due to isopropanol. The overall results indicated that isopropanol has an inhibitory effect on acetoclastic methanogenesis; and the inhibition can be detected by monitoring level of acetyl-CoA transcripts and rRNA level. (C) 2011 Elsevier B. V. All rights reserved.