Molecular analysis of methanogens involved in methanogenic degradation of tetramethylammonium hydroxide in full-scale bioreactors.

This study investigated methanogenic communities involved in degradation of tetramethylammonium hydroxide (TMAH) in three full-scale bioreactors treating TMAH-containing wastewater. Based on the results of terminal-restriction fragment-length polymorphism (T-RFLP) and quantitative PCR analyses targeting the methyl-coenzyme M reductase alpha subunit (mcrA) genes retrieved from three bioreactors, Methanomethylovorans and Methanosarcina were the dominant methanogens involved in the methanogenic degradation of TMAH in the bioreactors. Furthermore, batch experiments were conducted to evaluate mcrA messenger RNA (mRNA) expression during methanogenic TMAH degradation, and the results indicated that a higher level of TMAH favored mcrA mRNA expression by Methansarcina, while Methanomethylovorans could only express considerable amount of mcrA mRNA at a lower level of TMAH. These results suggest that Methansarcina is responsible for methanogenic TMAH degradation at higher TMAH concentrations, while Methanomethylovorans may be important at a lower TMAH condition.

Responses of ammonia-oxidizing archaeal and betaproteobacterial populations to wastewater salinity in a full-scale municipal wastewater treatment plant.

The diversity and abundance of ammonia-oxidizing Betaproteobacteria and archaea were investigated in a full-scale municipal wastewater treatment plant where the wastewater conductivity level varied considerably (due to seawater salinity intrusion) during this study between 2004 and 2007. Based on the quantitative polymerase chain reaction of ammonia monooxygenase subunit A (amoA) genes, an increase in the ammonia oxidizing bacteria amoA gene copies occurred with a decrease in the wastewater salinity level. A corresponding decrease in the average ammonia-oxidizing archaea to bacteria ratio, from 1.22 (2004 and 2005), 0.17 (2006), and then to 0.07 (2007), was observed. Phylogenetic analyses on amoA gene sequences indicated that Nitrosomonas marina-like ammonia oxidizing bacteria and Thaumarcheota Ⅰ.1a (marina group) ammonia-oxidizing archaea were dominant when the wastewater salinity level fluctuated at high values with an average of 4.83 practical salinity unit (psu), while Nitrosomonas urea-like ammonia oxidizing bacteria and Thaumarcheota Ⅰ.1b (soil group) ammonia-oxidizing archaea became dominant when the wastewater salinity decreased to a more stable lower level with an average of 1.93 psu. Based on the amoA gene-based terminal restriction fragment length polymorphism analyses, results from this study demonstrated that the observed shift in ammonia oxidizing bacteria and archaea populations is likely caused by a change of the wastewater salinity level.