Methanogen

About: Methanogen is a research topic. Over the lifetime, 1146 publications have been published within this topic receiving 48254 citations.

Dynamic shifts within volatile fatty acid–degrading microbial communities indicate process imbalance in anaerobic digesters

Abstract: Buildup of volatile fatty acids (VFAs) in anaerobic digesters (ADs) often results in acidification and process failure. Understanding the dynamics of microbial communities involved in VFA degradation under stable and overload conditions may help optimize anaerobic digestion processes. In this study, five triplicate mesophilic completely mixed AD sets were operated at different organic loading rates (OLRs; 1–6 g chemical oxygen demand [COD] LR−1day−1), and changes in the composition and abundance of VFA-degrading microbial communities were monitored using amplicon sequencing and taxon-specific quantitative PCRs, respectively. AD sets operated at OLRs of 1–4 g COD LR−1day−1 were functionally stable throughout the operational period (120 days) whereas process instability (characterized by VFA buildup, pH decline, and decreased methane production rate) occurred in digesters operated at ≥ 5 g COD LR−1day−1. Though microbial taxa involved in propionate (Syntrophobacter and Pelotomaculum) and butyrate (Syntrophomonas) degradation were detected across all ADs, their abundance decreased with increasing OLR. The overload conditions also inhibited the proliferation of the acetoclastic methanogen, Methanosaeta, and caused a microbial community shift to acetate oxidizers (Tepidanaerobacter acetatoxydans) and hydrogenotrophic methanogens (Methanoculleus). This study’s results highlight the importance of operating ADs with conditions that promote the maintenance of microbial communities involved in VFA degradation.

Early response of methanogenic archaea to H2 as evaluated by metagenomics and metatranscriptomics.

Abstract: The molecular machinery of the complex microbiological cell factory of biomethane production is not fully understood One of the process control elements is the regulatory role of hydrogen (H2) Reduction of carbon dioxide (CO2) by H2 is rate limiting factor in methanogenesis, but the community intends to keep H2 concentration low in order to maintain the redox balance of the overall system H2 metabolism in methanogens becomes increasingly important in the Power-to-Gas renewable energy conversion and storage technologies The early response of the mixed mesophilic microbial community to H2 gas injection was investigated with the goal of uncovering the first responses of the microbial community in the CH4 formation and CO2 mitigation Power-to-Gas process The overall microbial composition changes, following a 10 min excessive bubbling of H2 through the reactor, was investigated via metagenome and metatranscriptome sequencing The overall composition and taxonomic abundance of the biogas producing anaerobic community did not change appreciably 2 hours after the H2 treatment, indicating that this time period was too short to display differences in the proliferation of the members of the microbial community There was, however, a substantial increase in the expression of genes related to hydrogenotrophic methanogenesis of certain groups of Archaea As an early response to H2 exposure the activity of the hydrogenotrophic methanogenesis in the genus Methanoculleus was upregulated but the hydrogenotrophic pathway in genus Methanosarcina was downregulated The RT-qPCR data corroborated the metatranscriptomic H2 injection also altered the metabolism of a number of microbes belonging in the kingdom Bacteria Many Bacteria possess the enzyme sets for the Wood-Ljungdahl pathway These and the homoacetogens are partners for syntrophic community interactions between the distinct kingdoms of Archaea and Bacteria External H2 regulates the functional activity of certain Bacteria and Archaea The syntrophic cross-kingdom interactions in H2 metabolism are important for the efficient operation of the Power-to-Gas process Therefore, mixed communities are recommended for the large scale Power-to-Gas process rather than single hydrogenotrophic methanogen strains Fast and reproducible response from the microbial community can be exploited in turn-off and turn-on of the Power-to-Gas microbial cell factories

Fermentation studies with thermophilic Archaea in pure culture and in syntrophy with a thermophilic methanogen

Abstract: Two heterotrophic, thermophilic, sulfur-reducing archaea were isolated from the Guaymas Basin hydrothermal vent. The fermentation of proteinaceous and carbohydrate substrates was examined at 85°C for each isolate in the presence and absence of elemental sulfur and in coculture with a thermophilic methanogen. The heterotrophic isolates differed with respect to their requirement for sulfur. Both heterotrophic isolates exhibited a mixed organic acid fermentation from proteinaceous substrates; however, acetate was the sole organic acid produced from carbohydrate fermentation. In coculture fermentations with a thermophilic methanogen, the heterotrophic isolates exhibited enhanced growth and fermentation. Interspecies hydrogen transfer and elemental sulfur-reduction may be important microbial processes in deep-sea hydrothermal vent community metabolism.

The membraneless bioelectrochemical reactor stimulates hydrogen fermentation by inhibiting methanogenic archaea

Abstract: The membraneless bioelectrochemical reactor (Ml-BER) is useful for dark hydrogen fermentation. The effect of the electrochemical reaction on microorganisms in the Ml-BER was investigated using glucose as the substrate and compared with organisms in a membraneless non-bioelectrochemical reactor (Ml-NBER) and bioelectrochemical reactor (BER) with a proton exchange membrane. The potentials on the working electrode of the Ml-BER and BER with membrane were regulated to −0.9 V (versus Ag/AgCl) to avoid water electrolysis with a carbon electrode. The Ml-BER showed suppressed methane production (19.8 ± 9.1 mg-C·L−1·day−1) and increased hydrogen production (12.6 ± 3.1 mg-H·L−1·day−1) at pHout 6.2 ± 0.1, and the major intermediate was butyrate (24.9 ± 2.4 mM), suggesting efficient hydrogen fermentation. In contrast, the Ml-NBER showed high methane production (239.3 ± 17.9 mg-C·L−1·day−1) and low hydrogen production (0.2 ± 0.0 mg-H·L−1·day−1) at pHout 6.3 ± 0.1. In the cathodic chamber of the BER with membrane, methane production was high (276.3 ± 20.4 mg-C·L−1·day−1) (pHout, 7.2 ± 0.1). In the anodic chamber of the BER with membrane (anode-BER), gas production was low because of high lactate production (43.6 ± 1.7 mM) at pHout 5.0 ± 0.1. Methanogenic archaea were not detected in the Ml-BER and anode-BER. However, Methanosarcina sp. and Methanobacterium sp. were found in Ml-NBER. Prokaryotic copy numbers in the Ml-BER and Ml-NBER were similar, as were the bacterial community structures. Thus, the electrochemical reaction in the Ml-BER affected hydrogenotrophic and acetoclastic methanogens, but not the bacterial community.