Enrichment of denitrifying anaerobic methane oxidizing microorganisms

Abstract

The microorganisms responsible for anaerobic oxidation of methane (AOM) coupled to denitrification have not been clearly elucidated. Three recent publications suggested it can be achieved by a denitrifying bacterium with or without the involvement of anaerobic methanotrophic archaea. A key factor limiting the progress in this research field is the shortage of enrichment cultures performing denitrifying anaerobic methane oxidation (DAMO). In this study, DAMO cultures were enriched from mixed inoculum including sediment from a freshwater lake, anaerobic digester sludge and return activated sludge from a sewage treatment plant. Two reactors, operated at 35°C and at 22°C, respectively, showed simultaneous methane oxidation and nitrate reduction after several months of operation. Analysis of 16S rRNA gene clone libraries from the 35°C enrichment showed the presence of an archaeon closely related to other DAMO archaea and a dominated bacterium belonging to the yet uncultivated NC10 phylum. This culture preferred nitrite to nitrate as the electron acceptor. The present study suggests that the archaea are rather methanotrophs than methanogens. The highest denitrification rate achieved was 2.35 mmol NO3 (-) -N gVSS(-1) day(-1) . The culture enriched at 22°C contained the same NC10 bacterium observed in the culture enriched at 35°C but no archaea.

Potential roles of anaerobic ammonium and methane oxidation in the nitrogen cycle of wetland ecosystems

“…Molecular analysis of the biomass indicated the presence of two groups of microbes; about 15% of the biomass was made up of archaea distinctly related to the ANME archaea found in marine ecosystems, and about 80% of the cells were related to the NC10 phylum that has no isolated or cultured relatives. These finding were recently confirmed in a study using fresh water sediment and wastewater sludge as inoculum in Australia (Hu et al 2009). However, many 16S rRNA gene sequences similar to the sequence of denitrifying methanotrophs have now been retrieved from different anoxic freshwater sediments, indicating that denitrifying methanotrophic bacteria may be more widespread than previously assumed.…”

“…The wide range in growth temperature of anammox bacteria may promote their existence in wetlands. So far, the NC10 bacteria have only been detected in moderate fresh water sediments with temperatures between 10°C and 30°C (Ettwig et al 2008(Ettwig et al , 2009Hu et al 2009). …”

Evidence for nitrite-dependent anaerobic methane oxidation as a previously overlooked microbial methane sink in wetlands

“…Although several enrichment cultures of M. oxyfera-like bacteria have been obtained from freshwater sediments (1,(6)(7)(8) and peatlands (9), the distribution of these bacteria in environments is not well understood. Two recent studies reported the presence of M. oxyfera-like bacteria in two freshwater lakes, Lake Constance (10) in Germany and Lake Biwa in Japan (11).…”

Revisiting Methanotrophic Communities in Sewage Treatment Plants

“…High nitrite-driven anaerobic methane-oxidizing activity has so far been documented only in enrichment cultures of "C. Methylomirabilis oxyfera"-like microorganisms (41)(42)(43). Hence, we focused on aerobic methane oxidation in the natural community.…”