Methanogenic Microbial Community Research Articles

High synthetic cost-amino acids reduce member interactions of acetate-degrading methanogenic microbial community.

The cooperation among members of microbial communities based on the exchange of public goods such as 20 protein amino acids (AAs) has attracted widespread attention. However, little is known about how AAs availability affects interactions among members of complex microbial communities and the structure and function of a community. To investigate this question, trace amounts of AAs combinations with different synthetic costs (low-cost, medium-cost, high-cost, and all 20 AAs) were supplemented separately to acetate-degrading thermophilic methanogenic reactors, and the differences in microbial community structure and co-occurring networks of main members were compared to a control reactor without AA supplementation. The structure of the microbial community and the interaction of community members were influenced by AAs supplementation and the AAs with different synthetic costs had different impacts. The number of nodes, links, positive links, and the average degree of nodes in the co-occurrence network of the microbial communities with AAs supplementation was significantly lower than that of the control without AAs supplementation, especially for all 20 AAs supplementation followed by the medium- and high-cost AAs supplementation. The average proportion of positive interactions of microbial members in the systems supplemented with low-cost, medium-cost, high-cost, all AAs, and the control group were 0.42, 0.38, 0.15, 0.4, and 0.45, respectively. In addition, the ecological functions of community members possibly changed with the supplementation of different cost AAs. These findings highlight the effects of AAs availability on the interactions among members of complex microbial communities, as well as on community function.

Impact of dilution on stochastically driven methanogenic microbial communities of hypersaline anoxic sediments.

Sediments underlying the solar salterns of S'Avall are anoxic hypersaline ecosystems dominated by anaerobic prokaryotes, and with the especial relevance of putative methanogenic archaea. Slurries from salt-saturated sediments, diluted in a gradient of salinity and incubated for > 4 years revealed that salt concentration was the major selection force that deterministically structured microbial communities. The dominant archaea in the original communities showed a decrease in alpha diversity with dilution accompanied by the increase of bacterial alpha diversity, being highest at 5% salts. Correspondingly, methanogens decreased and in turn sulfate reducers increased with decreasing salt concentrations. Methanogens especially dominated at 25%. Different concentrations of litter of Posidonia oceanica seagrass added as a carbon substrate, did not promote any clear relevant effect. However, the addition of ampicillin as selection pressure exerted important effects on the assemblage probably due to the removal of competitors or enhancers. The amended antibiotic enhanced methanogenesis in the concentrations ≤ 15% of salts, whereas it was depleted at salinities ≥ 20% revealing key roles of ampicillin-sensitive bacteria.

Response of CO2 and CH4 emissions from Arctic tundra soils to a multifactorial manipulation of water table, temperature and thaw depth

Significant uncertainties persist concerning how Arctic soil tundra carbon emission responds to environmental changes. In this study, 24 cores were sampled from drier (high centre polygons and rims) and wetter (low centre polygons and troughs) permafrost tundra ecosystems. We examined how soil CO2 and CH4 fluxes responded to laboratory-based manipulations of soil temperature (and associated thaw depth) and water table depth, representing current and projected conditions in the Arctic. Similar soil CO2 respiration rates occurred in both the drier and the wetter sites, suggesting that a significant proportion of soil CO2 emission occurs via anaerobic respiration under water-saturated conditions in these Arctic tundra ecosystems. In the absence of vegetation, soil CO2 respiration rates decreased sharply within the first 7 weeks of the experiment, while CH4 emissions remained stable for the entire 26 weeks of the experiment. These patterns suggest that soil CO2 emission is more related to plant input than CH4 production and emission. The stable and substantial CH4 emission observed over the entire course of the experiment suggests that temperature limitations, rather than labile carbon limitations, play a predominant role in CH4 production in deeper soil layers. This is likely due to the presence of a substantial source of labile carbon in these carbon-rich soils. The small soil temperature difference (a median difference of 1 °C) and a more substantial thaw depth difference (a median difference of 6 cm) between the high and low temperature treatments resulted in a non-significant difference between soil CO2 and CH4 emissions. Although hydrology continued to be the primary factor influencing CH4 emissions, these emissions remained low in the drier ecosystem, even with a water table at the surface. This result suggests the potential absence of a methanogenic microbial community in high-centre polygon and rim ecosystems. Overall, our results suggest that the temperature increases reported for these Arctic regions are not responsible for increases in carbon losses. Instead, it is the changes in hydrology that exert significant control over soil CO2 and CH4 emissions.

Soil Properties Interacting With Microbial Metagenome in Decreasing CH4 Emission From Seasonally Flooded Marshland Following Different Stages of Afforestation.

Wetlands are the largest natural source of terrestrial CH4 emissions. Afforestation can enhance soil CH4 oxidation and decrease methanogenesis, yet the driving mechanisms leading to these effects remain unclear. We analyzed the structures of communities of methanogenic and methanotrophic microbes, quantification of mcrA and pmoA genes, the soil microbial metagenome, soil properties and CH4 fluxes in afforested and non-afforested areas in the marshland of the Yangtze River. Compared to the non-afforested land use types, net CH4 emission decreased from bare land, natural vegetation and 5-year forest plantation and transitioned to net CH4 sinks in the 10- and 20-year forest plantations. Both abundances of mcrA and pmoA genes decreased significantly with increasing plantation age. By combining random forest analysis and structural equation modeling, our results provide evidence for an important role of the abundance of functional genes related to methane production in explaining the net CH4 flux in this ecosystem. The structures of methanogenic and methanotrophic microbial communities were of lower importance as explanatory factors than functional genes in terms of in situ CH4 flux. We also found a substantial interaction between functional genes and soil properties in the control of CH4 flux, particularly soil particle size. Our study provides empirical evidence that microbial community function has more explanatory power than taxonomic microbial community structure with respect to in situ CH4 fluxes. This suggests that focusing on gene abundances obtained, e.g., through metagenomics or quantitative/digital PCR could be more effective than community profiling in predicting CH4 fluxes, and such data should be considered for ecosystem modeling.

Molecular Indicators of Sources and Biodegradation of Organic Matter in Sediments of Fluid Discharge Zones of Lake Baikal

This paper performs a detailed study of a wide set of organic-geochemical proxies in 15 sediment cores collected from the main basins of Lake Baikal (the northern, the central and the southern) where processes of focused fluid discharge were detected. A variety of studied zones includes sites with gas and hydrothermal seepage, mud volcanoes with or without gas-oil fluid discharge, gas hydrates and authigenic carbonates. The composition of the dispersed organic matter and individual hydrocarbon molecular markers (n-alkanes, dimethyl alkanes, isoprenoids, steranes, terpanes and polycyclic aromatic hydrocarbons) testify to the input from predominantly allochthonous terrestrial and autochthonous microbial and algal sources. The studied sources, maturity and biodegradation parameters of organic matter vary significantly for areas with different fluid discharge. The composition of specific biomarkers including isoprenoids and immature hopanoids reflects the lateral and vertical changes of microbial activity in sediments associated with various environmental conditions. The identified types of terpanes distribution (mature, mixed and immature) correlate well with types of fluid discharge and attest to the development of various methanogenic and methanotrophic microbial communities in sediments. Moreover, the revealed specificity of microbial molecular markers distribution allowed us to suggest the fluid discharge processes in zones where they were not previously detected.

Fractionation of stable carbon isotopes during acetate consumption by methanogenic and sulfidogenic microbial communities in rice paddy soils and lake sediments

Abstract. Acetate is an important intermediate during the degradation of organic matter in anoxic flooded soils and sediments. Acetate is disproportionated to CH4 and CO2 by methanogenic or is oxidized to CO2 by sulfate-reducing microorganisms. These reactions result in carbon isotope fractionation, depending on the microbial species and their particular carbon metabolism. To learn more about the magnitude of the isotopic enrichment factors (ε) involved, acetate conversion to CH4 and CO2 was measured in anoxic paddy soils from Vercelli (Italy) and the International Rice Research Institute (IRRI, the Philippines) and in anoxic lake sediments from the northeastern and the southwestern basins of Lake Fuchskuhle (Germany). Acetate consumption was measured using samples of paddy soil or lake sediment suspended in water or in phosphate buffer (pH 7.0), both in the absence and presence of sulfate (gypsum), and of methyl fluoride (CH3F), an inhibitor of aceticlastic methanogenesis. Under methanogenic conditions, values of εac for acetate consumption were always in a range of −21 ‰ to −17 ‰ but higher in the lake sediment from the southwestern basin (−11 ‰). Under sulfidogenic conditions εac values tended to be slightly lower (−26 ‰ to −19 ‰), especially when aceticlastic methanogenesis was inhibited. Again, εac in the lake sediment of the southwestern basin was higher (−18 ‰ to −14 ‰). Determination of εCH4 from the accumulation of 13C in CH4 resulted in much lower values (−37 ‰ to −27 ‰) than from the depletion of 13C in acetate (−21 ‰ to −17 ‰ ), especially when acetate degradation was measured in buffer suspensions. The microbial communities were characterized by sequencing the bacterial 16S rRNA (ribosomal ribonucleic acid) genes as well as the methanogenic mcrA and sulfidogenic dsrB genes. The microbial communities were quite different between lake sediments and paddy soils but were similar in the sediments of the two lake basins and in the soils from Vercelli and the IRRI, and they were similar after preincubation without and with addition of sulfate (gypsum). The different microbial compositions could hardly serve for the prediction of the magnitude of enrichment factors.

Contribution of periphytic biofilm of paddy soils to carbon dioxide fixation and methane emissions

Rice paddies are major contributors to anthropogenic greenhouse gas emissions via methane (CH4) flux. The accurate quantification of CH4 emissions from rice paddies remains problematic, in part due to uncertainties and omissions in the contribution of microbial aggregates on the soil surface to carbon fluxes. Herein, we comprehensively evaluated the contribution of one form of microbial aggregates, periphytic biofilm (PB), to carbon dioxide (CO2) and CH4 emissions from paddies distributed across three climatic zones, and quantified the pathways that drive net CH4 production as well as CO2 fixation. We found that PB accounted for 7.1%–38.5% of CH4 emissions and 7.2%–12.7% of CO2 fixation in the rice paddies. During their growth phase, PB fixed CO2 and increased the redox potential, which promoted aerobic CH4 oxidation. During the decay phase, PB degradation reduced redox potential and increased soil organic carbon availability, which promoted methanogenic microbial community growth and metabolism and increased CH4 emissions. Overall, PB acted as a biotic converter of atmospheric CO2 to CH4, and aggravated carbon emissions by up to 2,318 kg CO2 equiv ha−1 season−1. Our results provide proof-of-concept evidence for the discrimination of the contributions of surface microbial aggregates (i.e., PB) from soil microbes, and a profound foundation for the estimation and simulation of carbon fluxes in a potential novel approach to the mitigation of CH4 emissions by manipulating PB growth.

Sulfate-reducing and methanogenic microbial community responses during anaerobic digestion of tannery effluent

Microbial communities were monitored in terms of structure, function and response to physicochemical variables during anaerobic digestion of tannery and associated slaughterhouse effluent in: (i) 2 L biochemical methane potential batch reactors at different inoculum to substrate ratios (2–5) and initial sulfate concentrations (665–2000 mg/L), and (ii) 20 L anaerobic sequencing batch reactors with different mixing regimes (continuous vs. intermittent).Methanogenic and sulfidogenic community compositions in the 2 L reactors evolved initially, but stabilised after the start of biogas generation, although significant (ANOSIM p < 0.05) changes in the physicochemical parameters indicated continued metabolic activity. Both hydrogenotrophic and acetoclastic archaeal genera were present in high relative abundances. Continuous stirring preferentially selected the metabolically versatile genus Methanosarcina, suggesting that higher specific methane generation in the continuously stirred system (168 vs. 19.5 mL methane per gram volatile solids per week) was related to the metabolic activities of members of this genus.

Patterns of syntrophic interactions in methanogenic conversion of propionate.

Methanogenesis is central to anaerobic digestion processes. The conversion of propionate as a key intermediate for methanogenesis requires syntrophic interactions between bacterial and archaeal partners. In this study, a series of methanogenic enrichments with propionate as the sole substrate were developed to identify microbial populations specifically involved in syntrophic propionate conversion. These rigorously controlled propionate enrichments exhibited functional stability with consistent propionate conversion and methane production; yet, the methanogenic microbial communities experienced substantial temporal dynamics, which has important implications on the understanding of mechanisms involved in microbial community assembly in anaerobic digestion. Syntrophobacter was identified as the most abundant and consistent bacterial partner in syntrophic propionate conversion regardless of the origin of the source culture, the concentration of propionate, or the temporal dynamics of the culture. In contrast, the methanogen partners involved in syntrophic propionate conversion lacked consistency, as the dominant methanogens varied as a function of process condition and temporal dynamics. Methanoculleus populations were specifically enriched as the syntrophic partner at inhibitory levels of propionate, likely due to the ability to function under unfavorable environmental conditions. Syntrophic propionate conversion was carried out exclusively via transformation of propionate into acetate and hydrogen in enrichments established in this study. Microbial populations highly tolerant of elevated propionate, represented by Syntrophobacter and Methanoculleus, are of great significance in understanding methanogenic activities during process perturbations when propionate accumulation is frequently encountered. Key points • Syntrophobacter was the most consistent bacterial partner in propionate metabolism. • Diverse hydrogenotrophic methanogen populations could serve as syntrophic partners. • Methanoculleus emerged as a methanogen partner tolerant of elevated propionate.

Methanogenic Biodegradation of iso-Alkanes by Indigenous Microbes from Two Different Oil Sands Tailings Ponds.

iso-Alkanes, a major fraction of the solvents used in bitumen extraction from oil sand ores, are slow to biodegrade in anaerobic tailings ponds. We investigated methanogenic biodegradation of iso-alkane mixtures comprising either three (2-methylbutane, 2-methylpentane, 3-methylpentane) or five (2-methylbutane, 2-methylpentane, 2-methylhexane, 2-methylheptane, 2-methyloctane) iso-alkanes representing paraffinic and naphtha solvents, respectively. Mature fine tailings (MFT) collected from two tailings ponds, having different residual solvents (paraffinic solvent in Canadian Natural Upgrading Limited (CNUL) and naphtha in Canadian Natural Resources Limited (CNRL)), were amended separately with the two mixtures and incubated in microcosms for ~1600 d. The indigenous microbes in CNUL MFT produced methane from the three-iso-alkane mixture after a lag of ~200 d, completely depleting 2-methylpentane while partially depleting 2-methylbutane and 3-methylpentane. CNRL MFT exhibited a similar degradation pattern for the three iso-alkanes after a lag phase of ~700 d, but required 1200 d before beginning to produce methane from the five-iso-alkane mixture, preferentially depleting components in the order of decreasing carbon chain length. Peptococcaceae members were key iso-alkane-degraders in both CNUL and CNRL MFT but were associated with different archaeal partners. Co-dominance of acetoclastic (Methanosaeta) and hydrogenotrophic (Methanolinea and Methanoregula) methanogens was observed in CNUL MFT during biodegradation of three-iso-alkanes whereas CNRL MFT was enriched in Methanoregula during biodegradation of three-iso-alkanes and in Methanosaeta with five-iso-alkanes. This study highlights the different responses of indigenous methanogenic microbial communities in different oil sands tailings ponds to iso-alkanes.

Effectiveness of electromagnetic in situ magnetite capture in anaerobic sequencing batch treatment of dairy effluent under electro-syntrophic conditions

Adding conductive material has proven to be an effective way to promote direct interspecies electron transfer (DIET) and accelerate methanogenesis in anaerobic digestion processes. This study developed an automated sequencing batch reactor with a bottom-installed electromagnet and evaluated its effectiveness in enhancing the retention of magnetite (20 mM Fe) and biomass and maintaining enhanced methanogenesis. The reactor with electromagnetic in situ magnetite capture (RE) maintained better methanogenic performance and sludge settling than the reactor without it (RC) throughout the 19-month experiment at increasing organic loading rates (OLRs) (0.25–2.0 g chemical oxygen demand/L·d), particularly at higher OLRs. The washout loss of magnetite was not completely prevented in RE, although it was delayed compared with RC, suggesting the need for further research to minimize the loss of magnetite (and biomass aggregated therewith) for practical applications. DIET-based electro-syntrophic associations via magnetite-mediated electrical connections between cells appear to have developed in both reactors. Several (putative) electro-syntrophic microbes, for example, Methanothrix, Geobacter, Mesotoga, Smithella, Thermovirga, and Coriobacteriaceae species, occurred in both reactors; however, their relative abundance and distribution and the microbial community structure were significantly different between RC and RE, reflecting the effect of in situ magnetite capture on the development of methanogenic microbial community.

Effects of ferrous iron supplementation on reductive dechlorination of tetrachloroethene and on methanogenic microbial community.

ABSTRACTChloroethenes are common soil and groundwater pollutants. Their dechlorination is impacted by environmental factors, such as the presence of metal ions. We here investigated the effect of ferrous iron on bacterial reductive dechlorination of chloroethenes and on methanogen community. Reductive dechlorination of tetrachloroethene was assayed with a groundwater sample originally containing 6.3 × 103 copies mL−1 of Dehalococcoides 16S rRNA gene and 2 mg L−1 of iron. Supplementation with 28 mg L−1 of ferrous iron enhanced the reductive dechlorination of cis-dichloroethene (cis-DCE) and vinyl chloride in the presence of methanogens. The supplementation shortened the time required for complete dechlorination of 1 mg L−1 of tetrachloroethene to ethene and ethane from 84 to 49 d. Methanogens, such as Candidatus ‘Methanogranum’, Methanomethylovorans and Methanocorpusculum, were significantly more abundant in iron-supplemented cultures than in non-supplemented cultures (P < 0.01). Upon methanogen growth inhibition by 2-bromoethanesulfonate and in the absence of iron supplementation, cis-DCE was not dechlorinated. Further, iron supplementation induced 71.3% dechlorination of cis-DCE accompanied by an increase in Dehalococcoides 16S rRNA and dehalogenase vcrA gene copies but not dehalogenase tceA gene copies. These observations highlight the cooperative effect of iron and methanogens on the reductive dechlorination of chloroethenes by Dehalococcoides spp.

Activity and structure of methanogenic microbial communities in sediments of cascade hydropower reservoirs, Southwest China

Freshwater reservoirs are an important source of the greenhouse gas methane (CH4). However, little is known about the activity and structure of microbial communities involved in methanogenic decomposition of sediment organic matter (SOM) in cascade hydropower reservoirs. In this study, we targeted on sediments of three cascade reservoirs in Wujiang River, Southwest China. Our results showed that the content of sediment organic carbon (SOC) was between 3% and 11%, and it's positively correlated with both C/N ratio and recalcitrant organic carbon content of SOM. Meanwhile, SOC content was positively correlated with CH4 production rates but had no significant correlation with total CO2 production rates of the sediments, when rates were normalized to sediment volume. Resultantly, the sediment anaerobic decomposition rates hardly significantly increase along with the SOC content. These results suggested that the terrestrial organic matter accumulated after damming stimulated CH4 production from the reservoir sediments even though its decomposition rate was limited. Meantime, high throughput sequencing of 16S rRNA genes indicated that not only the hydrogenotrophic and acetoclastic, but also the methylotrophic methanogens (Methanomassiliicoccus) are abundant in the reservoir sediments. Moreover, metagenomic sequencing also suggested that methylotrophic methanogenesis are potentially important in the sediment of cascade reservoirs. Finally, the hydraulic residence time of the reservoir could be the key controlling factor of the structures of bacterial and archaeal communities as well as the CH4 production rates of the reservoir sediments.

Recognizing the pathways of microbial methanogenesis through methane isotopologues in the subsurface biosphere

Microbial methanogenesis is a significant component in the global carbon cycle, a driver of greenhouse warming from atmospheric methane, and contributes to natural gas resources. There are several metabolic pathways of methanogenesis, and it is challenging to discriminate between them and quantify their relative contributions in natural settings. Here we measure and compile four rare isotopologues of methane (13CH4, 12CH3D, 13CH3D and 12CH2D2) from the Qaidam Basin (China) and a large set of previous data across the world to identify distinctive fingerprints of two principal sources of subsurface microbial methane — hydrogenotrophic and methylotrophic methanogenesis — and use those fingerprints to deconvolve the budgets of microbial methane in the Qaidam Basin. Our data show that biogenic methanes in the Qaidam Basin have equilibrium Δ18/Δ13CH3D values respect to reservoir temperature without anaerobic methane oxidation. Our results suggest that methylotrophic methanogenesis produces methane with large deficits in 13CH3D and 12CH2D2 relative to that controlled by homogeneous equilibrium among methane isotopologues at ambient environmental temperatures, whereas hydrogenotrophic methanogenesis produces methane with 13CH3D abundance near equilibrium and relatively subtle 12CH2D2 deficits. We find a good linear correlation between the Δ13CH3D value of natural biogenic methane and independent estimates of the fraction of hydrogenotrophic (methylotrophic) methanogenesis, based on established interpretations of hydrogen isotope data. These findings are consistent with studies of laboratory cultures, which also show methylotrophic methane is more depleted in clumped isotopologues (13CH3D and 12CH2D2) than hydrogenotrophic methane, though both forms of cultured (hydrogenotrophic vs. methylotrophic) methane exhibit strong deficits in both isotopic species. The sensitivity of clumped isotopologues to methanogenesis pathways in natural settings provides a powerful tool for monitoring the activity of methanogenic microbial communities in the subsurface. Anomalies of both studied clumped isotopologues (Δ13CH3D and Δ12CH2D2) decrease over time in wells that have been re-sampled repeatedly, suggesting that such measurements are capable of detecting and quantifying shifts in proportions of these two metabolic pathways over the timescales of gas production history.

Winter Drainage and Plastic Film Mulching Mitigate CH &lt;sub&gt;4&lt;/sub&gt; Emission by Regulating Function and Structure of Methanogenic Microbial Communities in Paddy Soil

Winter Drainage and Plastic Film Mulching Mitigate CH &lt;sub&gt;4&lt;/sub&gt; Emission by Regulating Function and Structure of Methanogenic Microbial Communities in Paddy Soil

Ecogenomics Reveals Microbial Metabolic Networks in a Psychrophilic Methanogenic Bioreactor Treating Soy Sauce Production Wastewater.

An ecogenomic analysis of the methanogenic microbial community in a laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor treating soy sauce-processing wastewater revealed a synergistic metabolic network. Granular sludge samples were collected from the UASB reactor operated under psychrophilic (20°C) conditions with a COD removal rate >75%. A 16S rRNA gene amplicon sequencing-based microbial community analysis classified the major microbial taxa as Methanothrix, Methanobacterium, Pelotomaculaceae, Syntrophomonadaceae, Solidesulfovibrio, and members of the phyla Synergistota and Bacteroidota. Draft genomes of dominant microbial populations were recovered by metagenomic shotgun sequencing. Metagenomic- and metatranscriptomic-assisted metabolic reconstructions indicated that Synergistota- and Bacteroidota-related organisms play major roles in the degradation of amino acids. A metagenomic bin of the uncultured Bacteroidales 4484-276 clade encodes genes for proteins that may function in the catabolism of phenylalanine and tyrosine under microaerobic conditions. Syntrophomonadaceae and Pelotomaculaceae oxidize fatty acid byproducts presumably derived from the degradation of amino acids in syntrophic association with aceticlastic and hydrogenotrophic methanogen populations. Solidesulfovibrio organisms are responsible for the reduction of sulfite and may support the activity of hydrogenotrophic methanogens and other microbial populations by providing hydrogen and ammonia using nitrogen fixation-related proteins. Overall, functionally diverse anaerobic organisms unite to form a metabolic network that performs the complete degradation of amino acids in the psychrophilic methanogenic microbiota.

Sulfate-Reducing and Methanogenic Microbial Community Responses During Anaerobic Digestion of Tannery Effluent

Sulfate-Reducing and Methanogenic Microbial Community Responses During Anaerobic Digestion of Tannery Effluent

Impact of Organic Loading Rate on Performance and Methanogenic Microbial Communities of a Fixed-Bed Anaerobic Reactor at 4 °C

We investigated the feasibility of producing biogas in a fixed-bed anaerobic reactor at 4 °C with a gradual increase in organic loading rate (OLR). Reactor efficiency was highest when OLR was 4.33 kg/m3·d, whereas the reactor acidification occurred when OLR was 4.67 kg/m3·d. The values of methane content, biogas production, chemical oxygen demand (COD) removal rate, biogas production rate, acetic acid content, and propionic acid content were 69.3%, 5.33 L, 59.8%, 1.03 L/OLR, 0.17 g/L, and 1.15 g/L, respectively. The pH was stable and ranged from 7.2 to 6.8 when the reactor was operating at 4 °C during OLR increase. The 16S rRNA gene analysis revealed that the dominant archaea were Methanosaetaceae at 30 °C. At 4 °C, the dominant archaea were Methanomicrobiales, which were more abundant in adhering sludge compared to settled sludge. In conclusion, operating a fixed-bed anaerobic reactor at psychrophilic temperatures is more suitable.

Systems approach to the study of microbial methanogenesis in West-Siberian wetlands

This work is a lecture adapted to the format of a journal article on the course "Modern Topics in Biology", delivered by one of the authors in Yugra State University.&#x0D; The modern stage of the development of science and biology, in particular, is characterized by a systematic approach to the evaluation of various phenomena. In the concept of hierarchical holism, which dominates the systems approach, various biological systems form a hierarchical structure in which an element of one system is an independent system of a lower level. In any individual system, the key points are the interaction of its components and the structure that determines the stability of the system. The microbial systems of wetlands in West Siberia play a crucial ecological role in the context of the problem of greenhouse gases and changes in climate and atmospheric composition. The greenhouse gas methane entering the atmosphere is formed by the methanogenic microbial community, which is a complex biological system containing microbial groups which are closely related to each other by trophic interactions. The result of the work and the efficiency of the methanogenic microbial community is also determined by various physicochemical parameters of the environment. The main microbial agents responsible for the production of CH4 are methanogenic archaea, which are divided into three main trophic groups. The application of a systematic approach to the study of the methane cycle in wetlands of West Siberia allows us to comprehensively evaluate the vertical and horizontal system relationships, identify key elements and conduct a complex analysis of the problem under study.

Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes

AbstractThe release of long‐stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH4) clumped isotope (Δ18) and 14C measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that Δ18 values are negatively correlated with CH4 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH4 Δ18 and the fraction modern carbon. These correlations imply that CH4 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from Δ18 values, are not positively correlated with CH4 flux estimates, highlighting the likely importance of environmental variables other than CH4 production rates in controlling ebullition fluxes.