Showing papers on "Methanogenesis published in 2004"
TL;DR: Genetic analyses of methane-oxidizing Archaea from deep-sea sediments show that nearly all genes typically associated with methane production are present in one specific group of archaeal methanotrophs, which supports previous hypotheses and provides an informed foundation for metabolic modeling of anaerobic methane oxidation.
Abstract: Microbial methane consumption in anoxic sediments significantly impacts the global environment by reducing the flux of greenhouse gases from ocean to atmosphere. Despite its significance, the biological mechanisms controlling anaerobic methane oxidation are not well characterized. One current model suggests that relatives of methane-producing Archaea developed the capacity to reverse methanogenesis and thereby to consume methane to produce cellular carbon and energy. We report here a test of the “reverse-methanogenesis” hypothesis by genomic analyses of methane-oxidizing Archaea from deep-sea sediments. Our results show that nearly all genes typically associated with methane production are present in one specific group of archaeal methanotrophs. These genome-based observations support previous hypotheses and provide an informed foundation for metabolic modeling of anaerobic methane oxidation.
623 citations
TL;DR: In this paper, the authors used the Fourier Transform Spectrometer (FTS) at the Canada-France-Hawaii Telescope (CFIHT) to detect the absorption by martian methane at a 3.7 sigma level, which is exactly centered in the summed spectrum.
452 citations
TL;DR: The results suggest that microbial reduction of humic acid and subsequent chemical reduction of poorly soluble iron(III) minerals by the reduced humic acids represents an important path of electron flow in anoxic natural environments such as freshwater sediments.
342 citations
TL;DR: The higher performances on the volatile solid and pathogen reduction, and stable operation of the temperature co-phase anaerobic system might be attributable to the well-functioned thermophilic digester, sharing nutrients and intermediates for anaerilic microorganisms, and selection of higher substrate affinity an aerobic microorganisms in the co- phase system.
341 citations
TL;DR: The results show that both hydrogenotrophic and acetoclastic methanogenesis are an integral part of the CH4-producing pathway in acidic peat and were represented by appropriate methanogenic populations.
Abstract: Sites in the West Siberian peat bog 'Bakchar' were acidic (pH 4.2-4.8), low in nutrients, and emitted CH4 at rates of 0.2-1.5 mmol m(-2) h(-1). The vertical profile of delta13CH4 and delta13CO2 dissolved in the porewater indicated increasing isotope fractionation and thus increasing contribution of H2/CO2-dependent methanogenesis with depth. The anaerobic microbial community at 30-50 cm below the water table produced CH4 with optimum activity at 20-25 degrees C and pH 5.0-5.5 respectively. Inhibition of methanogenesis with 2-bromo-ethane sulphonate showed that acetate, phenyl acetate, phenyl propionate and caproate were important intermediates in the degradation pathway of organic matter to CH4. Further degradation of these intermediates indicated that 62-72% of the CH4 was ultimately derived from acetate, the remainder from H2/CO2. Turnover times of [2-14C]acetate were on the order of 2 days (15, 25 degrees C) and accounted for 60-65% of total CH4 production. Conversion of 14CO2 to 14CH4 accounted for 35-43% of total CH4 production. These results showed that acetoclastic and hydrogenotrophic methanogenesis operated closely at a ratio of approximately 2 : 1 irrespective of the incubation temperature (4, 15 and 25 degrees C). The composition of the archaeal community was determined in the peat samples by terminal restriction fragment length polymorphism (T-RFLP) analysis and sequencing of amplified SSU rRNA gene fragments, and showed that members of Methanomicrobiaceae, Methanosarcinaceae and Rice cluster II (RC-II) were present. Other, presumably non-methanogenic archaeal clusters (group III, RC-IV, RC-V, RC-VI) were also detected. Fluorescent in situ hybridization (FISH) showed that the number of Bacteria decreased (from 24 x 10(7) to 4 x 10(7) cells per gram peat) with depth (from 5 to 55 cm below the water table), whereas the numbers of Archaea slightly increased (from 1 x 10(7) to 2 x 10(7) cells per gram peat). Methanosarcina spp. accounted for about half of the archaeal cells. Our results show that both hydrogenotrophic and acetoclastic methanogenesis are an integral part of the CH4-producing pathway in acidic peat and were represented by appropriate methanogenic populations.
303 citations
TL;DR: A series of laboratory studies were conducted to increase understanding of stable carbon (13C/12C) and hydrogen (D/H) isotope fractionation arising from methanogenesis by moderately thermophilic acetate-and hydrogen-consuming methanogens as mentioned in this paper.
301 citations
TL;DR: Evidence accumulates that formate plays an even more important role in the conversion of propionate in obligate syntrophic consortia of acetogenic proton- and bicarbonate reducing bacteria and methanogenic archaea.
294 citations
TL;DR: Interestingly, acetate and formate were the major metabolic end products as shown by 13C NMR studies and enzymatic analysis of culture supernatants, strongly suggesting that M. acetivorans conserves energy by means of this acetogenic and formigenic process.
Abstract: All methanogenic Archaea examined to date rely on methanogenesis as their sole means of energy conservation. Among these are ones that use carbon monoxide as a growth substrate, producing methane via a pathway that involves hydrogen as an intermediate. To further examine the role of hydrogen in this process, we tested the ability of Methanosarcina acetivorans C2A, a metabolically versatile methanogen devoid of significant hydrogen metabolism, to use CO as a growth substrate. M. acetivorans grew on CO to high cell densities (≈1 × 108 per ml) with a doubling time of ≈24 h. Surprisingly, acetate and formate, rather than methane, were the major metabolic end products as shown by 13C NMR studies and enzymatic analysis of culture supernatants. Methane formation surpassed acetate/formate formation only when the cultures entered stationary growth phase, strongly suggesting that M. acetivorans conserves energy by means of this acetogenic and formigenic process. Resting cell experiments showed that methane production decreased linearly with increasing CO partial pressures, consistent with inhibition of methanogenesis by CO. Transposon-induced M. acetivorans mutants with lesions in the operon encoding phosphotransacetylase and acetate kinase failed to use either acetate or CO as growth substrates, indicating that these enzymes are required for both aceticlastic methanogenesis and carboxidotrophic acetogenesis. These findings greatly extend our concept of energy conservation and metabolic versatility in the methanogenic Archaea.
243 citations
TL;DR: Direct inhibition of methanogenesis by amorphous Fe(OH)3 at concentrations between 0 and 10 mM in experiments with pure cultures of methnogens is demonstrated and has important implications for kinetic modelling of microbial redox processes in anoxic soils and sediments.
173 citations
TL;DR: The function and structure of a methanogenic community in anoxic sediment of Lake Dagow, a eutrophic lake in north-eastern Germany, were studied, showing a higher contribution of H2-dependent methanogenesis and a lower contribution of acetate-dependent meethanogenesis at high versus low temperature.
Abstract: Methanogenic degradation of organic matter is an important microbial process in lake sediments Temperature may affect not only the rate but also the pathway of CH4 production by changing the activity and the abundance of individual microorganisms Therefore, we studied the function and structure of a methanogenic community in anoxic sediment of Lake Dagow, a eutrophic lake in north-eastern Germany Incubation of sediment samples (in situ 75°C) at increasing temperatures (4, 10, 15, 25, 30°C) resulted in increasing production rates of CH4 and CO2 and in increasing steady-state concentrations of H2 Thermodynamic conditions for H2/CO2 -dependent methanogenesis were only exergonic at 25 and 30°C Inhibition of methanogenesis with chloroform resulted in the accumulation of methanogenic precursors, ie, acetate, propionate, and isobutyrate Mass balance calculations indicated that less CH4 was formed via H2 at 4°C than at 30°C Conversion of 14CO2 to 14CH4 also showed that H2/CO2 -dependent methanogenesis contributed less to total CH4 production at 4°C than at 30°C [2–14 C]Acetate turnover rates at 4°C accounted for a higher percentage of total CH4 production than at 30°C Collectively, these results showed a higher contribution of H2-dependent methanogenesis and a lower contribution of acetate-dependent methanogenesis at high versus low temperature The archaeal community was characterized by cloning, sequencing, and phylogenetic analysis of the 16S rRNA genes retrieved from the sediment Sequences were affiliated with Methanosaetaceae, Methanomicrobiaceae, and three deeply branching euryarchaeotal clusters, ie, group III, Rice cluster V, and a novel euryarchaeotal cluster, the LDS cluster Terminal restriction fragment length polymorphism (T-RFLP) analysis showed that 16S rRNA genes affiliated to Methanosaetaceae (20–30%), Methanomicrobiaceae (35–55%), and group III (10–25%) contributed most to the archaeal community Incubation of the sediment at different temperatures (4–30°C) did not result in a systematic change of the archaeal community composition, indicating that change of temperature primarily affected the activity rather than the structure of the methanogenic community
161 citations
TL;DR: In spite of the relatively severe inhibition of the two anthraquinone dyes on the mixed, methanogenic culture, a high extent of color removal was achieved.
TL;DR: There is a very complex environment in which methane production, anaerobic methane oxidation, and aerobic methane oxidation all occur in close proximity, and several functional genes connected with methane metabolism were analyzed by quantitative competitive-PCR.
Abstract: Samples from three submerged sites (MC, a core obtained in the methane seep area; MR, a reference core obtained at a distance from the methane seep; and HC, a gas-bubbling carbonate sample) at the Kuroshima Knoll in the southern Ryuku arc were analyzed to gain insight into the organisms present and the processes involved in this oxic-anoxic methane seep environment. 16S rRNA gene analyses by quantitative real-time PCR and clone library sequencing revealed that the MC core sediments contained abundant archaea (approximately 34% of the total prokaryotes), including both mesophilic methanogens related to the genus Methanolobus and ANME-2 members of the Methanosarcinales, as well as members of the delta-Proteobacteria, suggesting that both anaerobic methane oxidation and methanogenesis occurred at this site. In addition, several functional genes connected with methane metabolism were analyzed by quantitative competitive-PCR, including the genes encoding particulate methane monooxygenase (pmoA), soluble methane monooxygenase (mmoX), methanol dehydrogenese (mxaF), and methyl coenzyme M reductase (mcrA). In the MC core sediments, the most abundant gene was mcrA (2.5 x 10(6) copies/g [wet weight]), while the pmoA gene of the type I methanotrophs (5.9 x 10(6) copies/g [wet weight]) was most abundant at the surface of the MC core. These results indicate that there is a very complex environment in which methane production, anaerobic methane oxidation, and aerobic methane oxidation all occur in close proximity. The HC carbonate site was rich in gamma-Proteobacteria and had a high copy number of mxaF (7.1 x 10(6) copies/g [wet weight]) and a much lower copy number of the pmoA gene (3.2 x 10(2) copies/g [wet weight]). The mmoX gene was never detected. In contrast, the reference core contained familiar sequences of marine sedimentary archaeal and bacterial groups but not groups specific to C1 metabolism. Geochemical characterization of the amounts and isotopic composition of pore water methane and sulfate strongly supported the notion that in this zone both aerobic methane oxidation and anaerobic methane oxidation, as well as methanogenesis, occur.
TL;DR: The increase of the specific methane yield for the full-scale biogas plant by applying thermal wet oxidation was 35-40%, showing that there is still a considerable amount of methane that can be harvested from anaerobic digested biowaste.
Abstract: Anaerobic digestion of solid biowaste generally results in relatively low methane yields of 50−60% of the theoretical maximum. Increased methane recovery from organic waste would lead to reduced handling of digested solids, lower methane emissions to the environment, and higher green energy profits. The objective of this research was to enhance the anaerobic biodegradability and methane yields from different biowastes (food waste, yard waste, and digested biowaste already treated in a full-scale biogas plant (DRANCO, Belgium)) by assessing thermal wet oxidation. The biodegradability of the waste was evaluated by using biochemical methane potential assays and continuous 3-L methane reactors. Wet oxidation temperature and oxygen pressure (T, 185−220 °C; O2 pressure, 0−12 bar; t, 15 min) were varied for their effect on total methane yield and digestion kinetics of digested biowaste. Measured methane yields for raw yard waste, wet oxidized yard waste, raw food waste, and wet oxidized food waste were 345, 685, 536, and 571 mL of CH4/g of volatile suspended solids, respectively. Higher oxygen pressure during wet oxidation of digested biowaste considerably increased the total methane yield and digestion kinetics and permitted lignin utilization during a subsequent second digestion. The increase of the specific methane yield for the full-scale biogas plant by applying thermal wet oxidation was 35−40%, showing that there is still a considerable amount of methane that can be harvested from anaerobic digested biowaste.
TL;DR: The flux of methane from a constructed wetland was determined over two growth seasons on a pilot scale wetland constructed to reduce nutrient levels in secondary treated wastewater, with large spatial and temporal variations that could be accounted for by measured environmental factors.
TL;DR: Phylogenetic analysis places the planctomycete sequences as distantly from their archaeal counterparts as from their proteobacterial counterparts, suggesting novel scenarios for the evolution of the C1 transfer functions in both methanogens and methylotrophs.
Abstract: Methanogenesis and methane oxidation are the major biological processes affecting the global cycling of the powerful greenhouse gas methane. To carry out the two alternative bioconversions, Nature has cleverly recycled key reactions for the C1 transfers between the oxidation levels of formaldehyde and formate, and these involve analogous enzyme systems and common specialized cofactors, methanopterin and methanofuran. Until recently, the distribution of these functions has been limited to methanogenic archaea and methylotrophic proteobacteria, and their evolutionary history remained obscure. Single interdomain lateral transfer of the respective genes has been suggested to play a role. Here we show that genes for C1 transfer reactions linked to methanopterin and methanofuran are also present in diverse representatives of the enigmatic bacterial clade, the Planctomycetes. Phylogenetic analysis places the planctomycete sequences as distantly from their archaeal counterparts as from their proteobacterial counterparts, suggesting novel scenarios for the evolution of the C1 transfer functions in both methanogens and methylotrophs. This finding suggests a possible role for Planctomycetes in the evolution of the methane cycle on Earth.
TL;DR: Results demonstrated that the dilution rate could cause a shift in the primary pathway of acetate conversion to methane in acetate-fed chemostats.
Abstract: Acetate conversion pathways of methanogenic consortia in acetate-fed chemostats at dilution rates of 0.025 and 0.6 day−1 were investigated by using 13C-labeled acetates, followed by gas chromatography-mass spectrometry (GC-MS) analysis of the CH4 and CO2 produced. Nonaceticlastic syntrophic oxidation by acetate-oxidizing syntrophs and hydrogenotrophic methanogens was suggested to occupy a primary pathway (approximately 62 to 90%) in total methanogenesis at the low dilution rate. In contrast, aceticlastic cleavage of acetate by aceticlastic methanogens was suggested to occupy a primary pathway (approximately 95 to 99%) in total methanogenesis at the high dilution rate. Phylogenetic analyses of transcripts of the methyl coenzyme M reductase gene (mcrA) confirmed that a significant number of transcripts of the genera Methanoculleus (hydrogenotrophic methanogens) and Methanosarcina (aceticlastic methanogens) were present in the chemostats at the low and high dilution rates, respectively. The mcrA transcripts of the genus Methanosaeta (aceticlastic methanogens), which dominated the population in a previous study (T. Shigematsu, Y. Tang, H. Kawaguchi, K. Ninomiya, J. Kijima, T. Kobayashi, S. Morimura, and K. Kida, J. Biosci. Bioeng. 96:547-558, 2003), were poorly detected at both dilution rates due to the limited coverage of the primers used. These results demonstrated that the dilution rate could cause a shift in the primary pathway of acetate conversion to methane in acetate-fed chemostats.
TL;DR: The results demonstrate the parallel change of microbial community structure and function in a complex environment, i.e., the increase of acetoclastic Methanosarcina spp.
Abstract: The community structure of methanogenic Archaea on anoxically incubated rice roots was investigated by amplification, sequencing, and phylogenetic analysis of 16S rRNA and methyl-coenzyme M reductase (mcrA) genes. Both genes demonstrated the presence of Methanomicrobiaceae, Methanobacteriaceae, Methanosarcinaceae, Methanosaetaceae, and Rice cluster I, an uncultured methanogenic lineage. The pathway of CH4 formation was determined from the 13C-isotopic signatures of the produced CH4, CO2 and acetate. Conditions and duration of incubation clearly affected the methanogenic community structure and the pathway of CH4 formation. Methane was initially produced from reduction of CO2 exclusively, resulting in accumulation of millimolar concentrations of acetate. Simultaneously, the relative abundance of the acetoclastic methanogens (Methanosarcinaceae, Methanosaetaceae), as determined by T-RFLP analysis of 16S rRNA genes, was low during the initial phase of CH4 production. Later on, however, acetate was converted to CH4 so that about 40% of the produced CH4 originated from acetate. Most striking was the observed relative increase of a population of Methanosarcina spp. (but not of Methanosaeta spp.) briefly before acetate concentrations started to decrease. Both acetoclastic methanogenesis and Methanosarcina populations were suppressed by high phosphate concentrations, as observed under application of different buffer systems. Our results demonstrate the parallel change of microbial community structure and function in a complex environment, i.e., the increase of acetoclastic Methanosarcina spp. when high acetate concentrations become available.
TL;DR: In this paper, the authors measured annual methane emission rates of 10gCH4yr 1 from the stands of Avicennia marina, which is of the same order of magnitude as rates from Northern wetlands.
Abstract: Mangroves have been considered for a long time to be a minor methane source, but recent reports have shown that polluted mangroves may emit substantial amounts of methane. In an unpolluted Indian mangrove, we measured annual methane emission rates of 10gCH4yr � 1 from the stands of Avicennia marina. This rate is of the same order of magnitude as rates from Northern wetlands. Methane emission from a freshwaterinfluenced area was higher, but was lower from a stunted mangrove growing on a hypersaline soil. Methane emission was mediated by the pneumatophores of Avicennia. This was consistent with the methane concentration in the aerenchyma, which decreased on average from 350ppmv in the cable roots to 10ppmv in the emergent part of the pneumatophores. However, the number of pneumatophores varied seasonally. The minimum number occurred during the monsoon season, which reduced methane emissions largely. Ebullition from unvegetated areas may also be important, at least during monsoon season when measured bubble fluxes were occasionally about five times as high as pneumatophore-mediated emissions.
TL;DR: Five inhibitors of methanogenesis are examined on CH4 production of the ruminal methanogens Methanobrevibacter ruminantium, Methanosarcina mazei and Methanomicrobium mobile to examine the effects of these inhibitors on methanogenic activity.
Abstract: Aims: To examine the effects of five inhibitors of methanogenesis, 2-bromoethanesulphonate (BES), 3-bromopropanesulphonate (BPS), lumazine, propynoic acid and ethyl 2-butynoate, on CH4 production of the ruminal methanogens Methanobrevibacter ruminantium, Methanosarcina mazei and Methanomicrobium mobile.
Methods and Results: Methanogens were grown in MS medium including 25% (v/v) clarified ruminal fluid. Methane production was measured after 4 and 6 days of incubation. Methanobrevibacter ruminantium was the most sensitive species to BES, propynoic acid and ethyl 2-butynoate. Methanosarcina mazei was the least sensitive species to those chemical additives, and Mm. mobile was intermediate. BPS failed to inhibit any of the methanogens. All three species were almost completely inhibited by 50- and 100%-lumazine saturated media, but the inhibition was somewhat lower with a 25%-lumazine saturated media.
Conclusions: There were important differences among species of methanogens regarding their sensitivity to the different inhibitors. In general, Ms. mazei was the most resistant to inhibitors, Mb. ruminantium the least resistant, and Mm. mobile was intermediate.
Significance and Impact of the Study: Differences among methanogens regarding their resistance to chemical inhibitors should be considered when designing strategies of inhibition of ruminal methanogenesis, as selection of resistant species may result.
TL;DR: A clear synergistic effect of mixtures of C12 and C14 in suppressing methanogenesis is demonstrated, mediated probably by direct inhibitory effects of the fatty acids on the methanogens.
Abstract: The interactions of lauric (C12) and myristic acid (C14) in suppressing ruminal methanogenesis and methanogens were investigated with the rumen simulation technique (Rusitec) using bovine ruminal fluid. The fatty acids were added to basal substrates (grass hay:concentrate, 1:1.5) at a level of 48 g/kg DM, provided in C12:C14 ratios of 5:0, 4:1, 3:2, 2.5:2.5, 2:3, 1:4 and 0:5. Additionally, an unsupplemented control consisting of the basal substrates only was employed. Incubation periods lasted for 15 (n 4) and 25 (n 2) d. CH4 formation was depressed by any fatty acid mixture containing at least 40 % C12, and effects persisted over the complete incubation periods. The greatest depression (70 % relative to control) occurred with a C12:C14 ratio of 4:1, whereas the second most effective treatment in suppressing CH4 production (60 % relative to control) was found with a ratio of 3:2. Total methanogenic counts were decreased by those mixtures of C12 and C14 also successful in suppressing methanogenesis, the 4:1 treatment being most efficient (60 % decline). With this treatment in particular, the composition of the methanogenic population was altered in such a way that the proportion of Methanococcales increased and Methanobacteriales decreased. Initially, CH4 suppression was associated with a decreased fibre degradation, which, however, was reversed after 10 d of incubation. The present study demonstrated a clear synergistic effect of mixtures of C12 and C14 in suppressing methanogenesis, mediated probably by direct inhibitory effects of the fatty acids on the methanogens.
TL;DR: Determination of biogeochemical controls and microbial consortia involved in TeCA degradation is leading to a better understanding of the heterogeneity in biodegradation rates and daughter product distribution in the wetland, improving capabilities for developing remediation and monitoring plans.
TL;DR: The results showed that initial spatial separation of food waste and inoculum enhances methane production and waste degradation in a one-stage solid-bed digester at high waste loading.
TL;DR: Atrazine degradation by anaerobic mixed culture microorganism in co-metabolic process and in absence of external carbon and nitrogen source was studied at influent atrazine concentration range of 0.5-15 mg/l to have much effect on the methanogenic bacteria which was clear from methane gas production and specific methnogenic activity (SMA).
TL;DR: 16S rRNA gene sequence analysis revealed that the isolate of a terephthalate-degrading bacterium, designated strain JT, was a member of subcluster Ih of the group ‘Desulfotomaculum lineage I', but it was only distantly related to other known species.
Abstract: The microbial populations responsible for anaerobic degradation of phthalate isomers were investigated by enrichment and isolation of those microbes from anaerobic sludge treating wastewater from the manufacturing of terephthalic acid. Primary enrichments were made with each of three phthalate isomers (ortho-, iso-, and terephthalate) as the sole energy source at 37°C with two sources of anaerobic sludge (both had been used to treat wastewater containing high concentrations of phthalate isomers) as the inoculum. Six methanogenic enrichment cultures were obtained which not only degraded the isomer used for the enrichment but also had the potential to degrade part of other phthalate isomers as well as benzoate with concomitant production of methane, presumably involving strictly syntrophic substrate degradation. Our 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that the predominant bacteria in the enrichment cultures were affiliated with a recently recognized non-sulfate-reducing subcluster (subcluster Ih) in the group ‘Desulfotomaculum lineage I9 or a clone cluster (group TA) in the class delta-Proteobacteria. Several attempts were made to isolate these microbes, resulting in the isolation of a terephthalate-degrading bacterium, designated strain JT, in pure culture. A coculture of the strain with the hydrogenotrophic methanogen Methanospirillum hungatei converted terephthalate to acetate and methane within 3 months of incubation, whereas strain JT could not degrade terephthalate in pure culture. During the degradation of terephthalate, a small amount of benzoate was transiently accumulated as an intermediate, indicative of decarboxylation of terephthalate to benzoate as the initial step of the degradation. 16S rRNA gene sequence analysis revealed that the strain was a member of subcluster Ih of the group ‘Desulfotomaculum lineage I9, but it was only distantly related to other known species.
TL;DR: It is found that both hydrogentrophic and aceticlastic methanogens are present in McLean Bog soils, and that methanogenic activity can be stimulated using H2/CO2 in the presence of rifampicin, or using low concentrations of acetate.
Abstract: Acidic peat bog soils produce CH4 and although molecular biological studies have demonstrated the presence of diverse methanogenic populations in them, few studies have sustained methanogenesis by adding the CH4 precursors H2/CO2 or acetate, and few indigenous methanogens have been cultured.McLeanBog is a small(ca. 70 m across), acidic (pH 3.4–4.3) Sphagnum-dominated bog in upstate New York. Although addition of H2/CO2 or 10m Macetate stimulated methanogenesis in soils from a nearby circumneutral pHfen, neither of these substrates led to sustained methanogenesis in McLean Bog soil slurries. After a brief period of stimulation by H2/CO2, methanogenesis in McLean Bog soil declined, which could be attributed to buildup of large amounts of acetic acid produced from the H2/CO2 by acetogens. Addition of the antibiotic rifampicin inhibited acetogenesis (carried out by Bacteria) and allowed methanogenesis (carried out by Archaea) to continue. Using rifampicin, we were able to study effects of temperature, pH, and salts on methanogenesis from H2/CO2 in McLean Bog soil samples.The enriched H2/CO2-utilizing methanogens showed an optimum for activity near pH 5, and a temperature optimum near 35?C.Methanogenesis was not stimulated by addition of 10 mM acetate,but it was stimulated by 1 mM acetate, and multiple additions were consumed at increasing rates and nearly stoichiometrically converted to CH4. In conclusion, we have found that both hydrogentrophic and aceticlastic methanogens are present in McLeanBog soils, and that methanogenic activity can be stimulated usingH2/CO2 in the presence of rifampicin, or using low concentrations of acetate.
Dissertation•
01 Jan 2004
TL;DR: In this paper, the authors investigated the profiles of hydrolytic enzymes, the distribution of the major volatile fatty acids produced in the acidification stage, the organic matter degradation, methane yield and the effect of co-digestion.
Abstract: The production of methane via anaerobic digestion of agricultural residues and industrial wastewater would benefit society by providing a clean fuel from renewable feedstocks. This would reduce the use of fossil-fuel-derived energy and reduce environmental impact, including global warming and pollution. Limitation of carbon dioxide and other emissions through emission regulations, carbon taxes, and subsidies on biomass energy is making anaerobic digestion a more attractive and competitive technology for waste(water) management. This thesis is concerned with some important aspects of anaerobic digestion of solid potato waste, sugar beet leaves and opaque beer brewery wastewater. Studies were performed using batch, one-stage and two-stage processes using laboratory-, pilot- and full-scale anaerobic reactors. For improved understanding of the anaerobic digestion of solid potato waste, some of the aspects investigated in this work were the profiles of hydrolytic enzymes, the distribution of the major volatile fatty acids produced in the acidification stage, the organic matter degradation, methane yield and the effect of co-digestion. During the hydrolysis of solid potato waste, both free and cell-bound hydrolytic enzyme activity was observed; amylase activity was found to be the highest followed by carboxylmethyl cellulase and filter paper cellulase. The fermentation products during batch anaerobic digestion of solid potato waste were chiefly acetic, butyric, propionic and lactic acid. The concentration and proportions of individual volatile fatty acids in the acidogenic stage are important in the overall performance of the anaerobic digestion system since acetic and butyric acids are the preferred precursors in methane formation. The performance of two-stage anaerobic digestion systems under mesophilic and thermophilic conditions showed that the digestion period for solid potato waste was shorter under thermophilic conditions than under mesophilic conditions; the concentrations of volatile fatty acids in the effluent of the second-stage thermophilic upflow anaerobic sludge blanket (UASB) reactor were no different from those in the effluent from the mesophilic UASB reactor. High rate reactors (packed-bed reactors with plastic and straw as biofilm carriers and a UASB reactor) were found to perform well during methanogenesis in two-stage anaerobic digestion of solid potato waste. The UASB performed better than the packed-bed reactor with plastic carriers. Straw, a common agricultural by-product, was confirmed to work well as a biofilm carrier. Employing efficient but low-cost technology is important for increased utilisation of anaerobic digestion, and the possibility of doing this has been demonstrated by a simple pilot-scale, two-stage anaerobic digestion system for the treatment of solid potato waste and sugar beet leaves, alone and combined, with the recovery of biogas. Co-digestion of solid potato waste and sugar beet leaves improved the methane yield by 60% compared with that from digestion of the separate substrates in both batch and pilot-scale studies. Results from this work suggest that potato waste and sugar beet leaves are suitable substrates for anaerobic digestion giving high biogas yields, and could provide additional benefits to farmers. The performance of a full-scale UASB reactor treating opaque beer brewery wastewater investigated over a period of two years enabled the brewery to meet the requirements for wastewater discharged into the municipal sewage system of Harare, Zimbabwe. The installation of a high-rate reactor by the brewery is an attractive economic and environmental alternative considering that an era of critical energy shortage, substantially higher energy prices and high demand on environmental protection lies ahead. (Less)
TL;DR: The results of integrated elemental and isotope analyses of Antrim Shale formation waters from the margins and center of the Michigan Basin, focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis are presented in this article.
Abstract: The Upper Devonian Antrim Shale in the Michigan Basin is an economically significant source of microbially produced methane along the basin margins where meteoric recharge has been focused. Oxygen and hydrogen stable isotope compositions of Antrim formation waters show that fresh waters, recharged from Pleistocene glaciation and modern precipitation, suppressed basinal brine salinity to great depths and enhanced methanogenesis. This paper presents results of integrated elemental and isotope analyses of Antrim Shale formation waters from the margins and center of the Michigan Basin, focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis. Cl-Br-Na systematics reveal that salinity is controlled not only by mixing between variable amounts of basinal brine and meteoric water, but also by halite dissolution where fluids recharged through underlying Devonian carbonate aquifers with localized evaporite deposits. Divalent cations, carbonate system parameters, and carbon isotope compositions of dissolved inorganic carbon have been systematically and profoundly altered by microbial methanogenesis. Large decreases in formation water Ca/Mg and Ca/Sr ratios accompany increasing carbonate alkalinity values in areas with high rates of microbial gas production. Thermodynamic and reaction-path modeling show that these changes are consistent with calcite precipitation during progressive microbial methanogenesis. Similar variations in fluid chemistry are evident in databases from other sedimentary basins containing black shales and coal beds associated with microbial gas. Microbial methanogenesis may play an important role in the geochemical evolution of divalent cation relationships in crustal fluids and should be considered in models of formation water origin and evolution.
TL;DR: Results coupled with consideration of hydrogen thresholds, degradation kinetics, daughter products, and measurements of methanogenesis strongly suggest that halorespirers were responsible for dechlorination of cis-1,2-DCE and that 1,2 -DCA de chlorination was co-metabolic, likely mediated by acetogens or methanogens.
Abstract: Anaerobic degradation of cis-1,2-dichloroethene (cis-1,2-DCE) and 1,2-dichloroethane (1,2-DCA) was studied in microcosms derived from a laboratory-scale upflow treatment wetland system used to biodegrade chlorinated compounds present in groundwater from a Superfund site. Dechlorination kinetics of cis-1,2-DCE (0.94-1.57 d(-1)) and 1,2-DCA (0.15-0.71 d(-1)) were rapid, and degradation proceeded to completion with ethene or ethane as terminal dechlorination products. Hydrogen concentrations, measured simultaneously during dechlorination, were significantly different for the two compounds, approximately 2.5 nM for cis-1,2-DCE and 38 nM for 1,2-DCA. Methanogenesis proceeded during the degradation of 1,2-DCA when H2 concentrations were high but not during the dechlorination of cis-1,2-DCE when H2 concentrations were below published thresholds for methanogenesis. A 16S rRNA gene-based approach indicates that microorganisms closely related to Dehalococcoides ethenogenes were present and that they were distributed throughout the bottom, middle, and top of the upflow treatment wetland system. These results coupled with consideration of hydrogen thresholds, degradation kinetics, daughter products, and measurements of methanogenesis strongly suggest that halorespirers were responsible for dechlorination of cis-1,2-DCE and that 1,2-DCA dechlorination was co-metabolic, likely mediated by acetogens or methanogens. Rapid dechlorination potential was distributed throughout the wetland bed, both within and below the rhizosphere, indicating that reductive dechlorination pathways can be active in anaerobic environments located in close spatial proximity to aerobic environments and plants in treatment wetland systems.
TL;DR: In this article, the effects of 1-4 galacto-oligosaccharides (GOS) or nisin in combination with nitrate were assessed on rumen methanogenesis, intoxication by nitrate, and metabolic rate in nitrate-treated sheep.