Single and multiple effects of organic solvents on the expression level of acetyl-CoA synthetase gene and active methanogenic population

Abstract

Organic chemicals which are used as solvent in most of the industries may have inhibitory effects on microorganisms. Since acetoclastic methanogens play an important role in stabilizing the pollution load of wastewater by participating in the terminal methanogenesis step, defining effects of solvents on both microbial community structure and acetoclastic pathway in anaerobic reactors can lead to improvements in understanding of interactions in the bioreactors, thereby obtaining better reactor performance in terms of higher degradation capacity and biogas production. In this study, effects of solvents such as methanol (0.1-1.0 M), toluene (0.5- 4.0 mM), iso-propanol (0.1-2.0 M) and toluene + methanol (0.5 mM + 1.0 M, 1.5 mM + 1.0 M) on methane production, expression level of acetly-CoA synthetase gene and viable microbial populations were studied in sludges taken from batch reactors. Within the scope of this study, it was found that biogas productions of the reactors decreased with increasing concentrations of the solvents. The most severe effects of solvents were observed for the iso-propanol and toluene + methanol added reactors, respectively. It was also found that the expression of acetyl-CoA synthetase genes of Methanosaeta remained quite unchanged after exposures to methanol and methanol + toluene added reactors whereas no expression was detected for toluene and iso-propanol added reactors. The percentage of active microbial populations generally increased by the increasing concentrations of solvents. Methanosaeta usually dominated in the reactors. The dominance of Methanosaeta was followed by Methanobacteriales which was usually resistant to higher concentrations and observed to be dominating genus in toluene added reactor.|Keywords: organic solvents, inhibition, acetyl-CoA synthetase, methanogen, Q-PCR