Explore the vast range of titles available.

Methyl-coenzyme M reductase, the rate-limiting enzyme in methanogenesis and anaerobic methane oxidation, is responsible for the biological production of more than 1 billion tons of methane per year. The mechanism of methane synthesis is thought to involve either methylnickel(III) or methyl radical/Ni(II)-thiolate intermediates. We employed transient kinetic, spectroscopic, and computational approaches to study the reaction between the active Ni(I) enzyme and substrates. Consistent with the methyl radical–based mechanism, there was no evidence for a methyl-Ni(III) species; furthermore, magnetic circular dichroism spectroscopy identified the Ni(II)-thiolate intermediate. Temperature-dependent transient kinetics also closely matched density functional theory predictions of the methyl radical mechanism. Identifying the key intermediate in methanogenesis provides fundamental insights to develop better catalysts for producing and activating an important fuel and potent greenhouse gas.

Wetlands are the largest individual source of methane (CH₄), but the magnitude and distribution of this source are poorly understood on continental scales. We isolated the wetland and rice paddy contributions to spaceborne CH₄ measurements over 2003-2005 using satellite observations of gravity anomalies, a proxy for water-table depth Γ, and surface temperature analyses TS. We find that tropical and higher-latitude CH₄ variations are largely described by Γ and TS variations, respectively. Our work suggests that tropical wetlands contribute 52 to 58% of global emissions, with the remainder coming from the extra-tropics, 2% of which is from Arctic latitudes. We estimate a 7% rise in wetland CH₄ emissions over 2003-2007, due to warming of mid-latitude and Arctic wetland regions, which we find is consistent with recent changes in atmospheric CH₄.

Methanogens are methane-producing, hydrogen-oxidizing (i.e. hydrogenotrophic) archaea. Numerous studies have associated methanogens with obesity, but these results have been inconsistent. One link to metabolism may be methanogens’ hydrogen-oxidizing ability, thus reducing hydrogen partial pressure and thermodynamically enhancing fermentation of sugars to short-chain fatty acids (SCFAs) that the host can absorb. Because research linking methanogenesis to human metabolism is limited, our goal with this exploratory analysis was to investigate relationships between methanogens and other hydrogenotrophs, along with the association of methanogens with human metabolizable energy (ME). Using results from a randomized crossover feeding study including a western diet and a high-fiber diet, well-characterized human participants, and continuous methane measurements, we analyzed hydrogenotroph abundance and activity, fecal and serum SCFAs, and host ME between high and low methane producers. We detected methanogens in about one-half of participants. We found no evidence that methanogens’ consumption of hydrogen to produce methane affected other hydrogenotrophs. High methane producers had greater serum propionate and greater gene and transcript abundance of a key enzyme of the hydrogen-consuming, propionate-producing succinate pathway. High methane producers also had greater ME than low producers on the high-fiber diet. A network analysis revealed positive relationships between the methane-production rate and bacteria capable of degrading fiber and fermenting fiber-degradation products, thus forming a trophic chain to extract additional energy from undigested substrates. Our results show that methanogenesis in a microbial consortium was linked to host ME through enhanced microbial production, and subsequent host absorption, of SCFAs.

A mesophilic anaerobic moving bed biofilm reactor (MBBR) was operated to evaluate the effect of sulfate addition on methane production and sulfate reduction using acetate as the sole carbon source. The results show that at the organic loading rate of 4.0 g TOC/L/day, the TOC removal efficiencies and the biogas production rates achieved over 95 % and 7000 mL/L/day without sulfate, respectively, and slightly decreased with sulfate addition (500–800 mg/L). Methane production capacities were not influenced significantly with the addition of sulfate, while sulfate reduction efficiencies were not stable with 23–87 % in the acetate-fed reactor. Fluorescent in situ hybridization (FISH) was used to analyze the functional microbial compositions of acetate-degrading methane-producing bacteria (MPB) and sulfate-reducing bacteria (SRB) in the reactor. The results found that as the increase of sulfate concentration, the proportion of Methanomicrobiales increased up to 58 ± 2 %, while Methanosaeta and Methanosarcina decreased. The dominant methanogens shifted into hydrogenotrophic methanogens from even distribution of acetoclastic and hydrogenotrophic methanogens. When hydrogenotrophic methanogens were dominant, sulfate reduction efficiency was high, while sulfate reduction efficiency was low as acetoclastic methanogens were dominant.

This study aimed to investigate the interaction between methane production performance and active microbial community dynamics at different loading rates by increasing influent substrate concentration. The model system was an upflow anaerobic sludge blanket (UASB) reactor using molasses wastewater. The active microbial community was analyzed using a ribosomal RNA-based approach in order to reflect active members in the UASB system. The methane production rate (MPR) increased with an increase in organic loading rate (OLR) from 3.6 to 5.5 g COD·L −1 ·day −1 and then it decreased with further OLR addition until 9.7 g COD·L −1 ·day −1 . The UASB reactor achieved a maximum methane production rate of 0.48 L·L −1 ·day −1 with a chemical oxygen demand (COD) removal efficiency of 91.2 % at an influent molasses concentration of 16 g COD·L −1 (OLR of 5.5 g COD·L −1 ·day −1 ). In the archaeal community, Methanosarcina was predominant irrespective of loading rate, and the relative abundance of Methanosaeta increased with loading rate. In the bacterial community, Firmicutes and Eubacteriaceae were relatively abundant in the loading conditions tested. The network analysis between operation parameters and microbial community indicated that MPR was positively associated with most methanogenic archaea, including the relatively abundant Methanosarcina and Methanosaeta , except Methanofollis . The most abundant Methanosarcina was negatively associated with Bifidobacterium and Methanosaeta , whereas Methanosaeta was positively associated with Bifidobacterium .

Fruit waste is a potential feedstock for biogas production. However, the presence of fruit flavors that have antimicrobial activity is a challenge for biogas production. Lactones, ketones, and phenolic compounds are among the several groups of fruit flavors that are present in many fruits. This work aimed to investigate the effects of two lactones, i.e., γ-hexalactone and γ-decalactone; two ketones, i.e., furaneol and mesifurane; and two phenolic compounds, i.e., quercetin and epicatechin on anaerobic digestion with a focus on methane production, biogas composition, and metabolic intermediates. Anaerobic digestion was performed in a batch glass digester incubated at 55 °C for 30 days. The flavor compounds were added at concentrations of 0.05, 0.5, and 5 g/L. The results show that the addition of γ-decalactone, quercetin, and epicathechin in the range of 0.5–5 g/L reduced the methane production by 50 % (MIC₅₀). Methane content was reduced by 90 % with the addition of 5 g/L of γ-decalactone, quercetin, and epicathechin. Accumulation of acetic acid, together with an increase in carbon dioxide production, was observed. On the contrary, γ-hexalactone, furaneol, and mesifurane increased the methane production by 83–132 % at a concentration of 5 g/L.

The aim of this study was to evaluate the effect of adding different concentrations of either urea or NaOH in dehydrated acerola (Malpighia emarginata) fruit residue (DAFR) on chemical composition, in vitro rumen degradability, and gas and methane production. A completely randomized design was used with the following seven treatments: control, without chemical treatment, or pretreatment of DAFR with urea or NaOH at 20, 40, or 60 g/kg dry matter (DM). DM degradability and gas and methane production of DAFR were evaluated by semi-automated in vitro gas production technique. DAFR treated with urea or NaOH at concentrations of 40 and 60 g/kg DM decreased its neutral detergent fiber (P = 0.0115) and lignin (P < 0.0001) content, and this reduction was greater with the highest concentration (60 g/kg DM). In all tested concentrations, urea and NAOH were effective to increase the DM effective degradability of DAFR compared with the control treatment, although treatments with a concentration of 60 g/kg DM presented the highest values (P < 0.0001). Treatment of DAFR with NaOH or urea at 60 g/kg DM promotes greater lignin solubilization and DM degradability and lower gas and methane production in in vitro rumen fermentation.

Forest ecosystem methane (CH₄) research has focused on soils, but trees are also important sources and sinks in forest CH₄ budgets. Living and dead trees transport and emit CH₄ produced in soils; living trees and dead wood emit CH₄ produced inside trees by microorganisms; and trees produce CH₄ through an abiotic photochemical process. Here, we review the state of the science on the production, consumption, transport, and emission of CH₄ by living and dead trees, and the spatial and temporal dynamics of these processes across hydrologic gradients inclusive of wetland and upland ecosystems. Emerging research demonstrates that tree CH₄ emissions can significantly increase the source strength of wetland forests, and modestly decrease the sink strength of upland forests. Scaling from stem or leaf measurements to trees or forests is limited by knowledge of the mechanisms by which trees transport soil-produced CH₄, microbial processes produce and oxidize CH₄ inside trees, a lack of mechanistic models, the diffuse nature of forest CH₄ fluxes, complex overlap between sources and sinks, and extreme variation across individuals. Understanding the complex processes that regulate CH₄ source–sink dynamics in trees and forests requires cross-disciplinary research and new conceptual models that transcend the traditional binary classification of wetland vs upland forest.

Methanogenic and methanotrophic archaea play important roles in the global flux of methane. Culture-independent approaches are providing deeper insight into the diversity and evolution of methane-metabolizing microorganisms, but, until now, no compelling evidence has existed for methane metabolism in archaea outside the phylum Euryarchaeota. We performed metagenomic sequencing of a deep aquifer, recovering two near-complete genomes belonging to the archaeal phylum Bathyarchaeota (formerly known as the Miscellaneous Crenarchaeotal Group). These genomes contain divergent homologs of the genes necessary for methane metabolism, including those that encode the methyl–coenzyme M reductase (MCR) complex. Additional non-euryarchaeotal MCR-encoding genes identified in a range of environments suggest that unrecognized archaeal lineages may also contribute to global methane cycling. These findings indicate that methane metabolism arose before the last common ancestor of the Euryarchaeota and Bathyarchaeota.