Anaerobic oxidation of methane (AOM) driven by multiple electron acceptors in constructed wetland and the related mechanisms of carbon, nitrogen, sulfur cycles

High-throughput experimental technologies often identify dozens to hundreds of genes related to, or changed in, a biological or pathological process. From these genes one wants to identify biological pathways that may be involved and diseases that may be implicated. Here, we report a web server, KOBAS 2.0, which annotates an input set of genes with putative pathways and disease relationships based on mapping to genes with known annotations. It allows for both ID mapping and cross-species sequence similarity mapping. It then performs statistical tests to identify statistically significantly enriched pathways and diseases. KOBAS 2.0 incorporates knowledge across 1327 species from 5 pathway databases (KEGG PATHWAY, PID, BioCyc, Reactome and Panther) and 5 human disease databases (OMIM, KEGG DISEASE, FunDO, GAD and NHGRI GWAS Catalog). KOBAS 2.0 can be accessed at http://kobas.cbi.pku.edu.cn.

Carbon and nitrogen cycles have been altered dramatically by human activities. Methane-producing (methanogenic) and methane-consuming (methanotrophic) microorganisms control the emission of methane, one of the most potent greenhouse gases, to the atmosphere. Earlier studies identified methanotrophic microorganisms that use methane as an electron donor and oxygen, sulfate, nitrite, and nitrate as electron acceptors. Previous research showed that methanotrophy coupled to the reduction of oxidized metals could be important in the environment. In the current paper, we identified archaea of the order Methanosarcinales , related to “ Candidatus Methanoperedens nitroreducens,” which couple the reduction of environmentally relevant particulate forms of iron and manganese to methane oxidation, filling one of the remaining lacunas in anaerobic methane oxidation. Anaerobic oxidation of methane (AOM) is crucial for controlling the emission of this potent greenhouse gas to the atmosphere. Nitrite-, nitrate-, and sulfate-dependent methane oxidation is well-documented, but AOM coupled to the reduction of oxidized metals has so far been demonstrated only in environmental samples. Here, using a freshwater enrichment culture, we show that archaea of the order Methanosarcinales , related to “ Candidatus Methanoperedens nitroreducens,” couple the reduction of environmentally relevant forms of Fe 3+ and Mn 4+ to the oxidation of methane. We obtained an enrichment culture of these archaea under anaerobic, nitrate-reducing conditions with a continuous supply of methane. Via batch incubations using [ 13 C]methane, we demonstrated that soluble ferric iron (Fe 3+ , as Fe-citrate) and nanoparticulate forms of Fe 3+ and Mn 4+ supported methane-oxidizing activity. CO 2 and ferrous iron (Fe 2+ ) were produced in stoichiometric amounts. Our study connects the previous finding of iron-dependent AOM to microorganisms detected in numerous habitats worldwide. Consequently, it enables a better understanding of the interaction between the biogeochemical cycles of iron and methane.