Inhibition Of Methanogenesis Research Articles

Effects of free nitrous acid and freezing co-pretreatment on sludge short-chain fatty acids production and dewaterability

Short-chain fatty acids (SCFAs) as recoverable carbon source from waste activated sludge anaerobic fermentation process have aroused wide concern. In this study, free nitrous acid (FNA) and freezing pretreatments were combined to enhance SCFAs yield and fermented sludge dewaterability in the anaerobic fermentation system. The effects of different FNA concentrations and different freezing conditions (with or without curing stages) were analysed and compared. The results indicated that combining 1.07 mg N/L FNA with 48 h continuous freezing at −5 °C, raised SCFAs production from 6.7 mg COD/g volatile suspended solids (VSS) for the blank (no pretreatment) up to 124.0 mg COD/g VSS. In addition, the minimal water content of the treated fermented sludge cake was 78.11%, which was less than that of the blank (81.22%). SCFAs production and dewaterability enhancement could be attributed to sludge disintegration induced by the co-pretreatment, which led to sludge solubilisation, organics release, methanogenesis inhibition and particle size variation. This study implied that FNA and freezing co-pretreatment has the potential to enhance SCFAs production and sludge dewaterability in wastewater treatment plants.

The effect of seaweed (Gracilaria sp.) supplementation in sheep feed on methanogenesis inhibition in vitro

The study aimed to assess the optimal level of supplementation of seaweed Gracilaria sp. in sheep feed on total gas, methane gas, methanogen and protozoa populations, digestibility of dry matter and organic matter. The research material used was rumen fluid from 3 sheep. The treatment tested was supplementation of seaweed flour Gracilaria sp. with a level of 0% (P0), 2% (P1), 4% (P2), 6% (P3) and 8% (P4) based on feed DM which was composed of forage Cynodon dactylon (60%) and concentrate (40%). The study design used a completely randomized design, each treatment was repeated 4 times. The variables measured are total gas, methane gas, methanogen population, protozoa population, dry matter and organic matter digestibility. The results showed that the supplementation of Gracilaria sp seaweed decreased (P <0.05) total gas, methane gas, methanogen population, protozoa population and increased (P<0.05) digestibility of dry matter and organic matter. Conclusions, seaweed supplementation up to the level of 3.6% (DM) effective inhibited the level of methanogenesis giving varying influences.

Mesophilic Anaerobic Co-digestion of Olive-Mill Waste With Cattle Manure: Effects of Mixture Ratio

The co-digestion of agri-food by-products and livestock manure is a feasible alternative for waste management and the recovery of biogas provides an option to generate renewable energy. A series of batch experiments were carried out in order to investigate the mesophilic anaerobic co-digestion of two-phase olive-mill waste (2POMW) and cattle manure (CM) in different mixtures (2POMW:CM = 50:50; 60:40; 75:25; 85:15). In addition, the biodegradability of the co-substrates was studied in order to analyze the performance of the co-digestion process. The results obtained in this study indicate that 2POMW has a low biodegradability since a high soluble organic matter concentration and a low accumulated methane production were obtained at the end of the corresponding biodegradability test. However, CM is more easily biodegradable in mesophilic anaerobic conditions. The co-digestion of both wastes produced an enhancement of the hydrolytic-acidogenic phase, increasing the organic matter potentially bioavailable as volatile fatty acids (VFAs) and the biogas productivity, as a consequence of the subsequent degradation of VFAs by methanogens. However, an accumulation of VFA, principally propionic acid, was observed in the reactors with higher proportions of 2POMW. The volatile solids (VS) removal increased with the 2POMW percentage of the mixture up to 75% fresh weight. The increase of 2POMW above 75% led to a decrease in total VS removal. Moreover, a decrease in methane production was observed for the 85:15 mixture, as a consequence of the high concentration of propionic acid, which is a known inhibitor of methanogenesis. The maximum cumulative methane production and methane yield were achieved in the 75:25 mixture with values of 18.70 L and 112.40 LCH4/kgVSadded, respectively. Compared with 2POMW, the co-digestion produced an increase of 264-319% in the volume of accumulated methane (L), 293-351% in the methane yield (LCH4/kgVSadded) and 312-342% based on the VS consumed (LCH4/kgVSremoved). These results suggest that the mixture of these agro-industrial by-products could be effective to enhance biogas production and organic matter removal from 2POMW.

Biochar promotes methane production at high acetate concentrations in anaerobic soils

Methane (CH4) is a major greenhouse gas emitted by the industry, agriculture and natural processes such as degradation of organic matter in anaerobic waters and soils. Addition of biochars to soils has been investigated to control greenhouse gas emission, but actually there are still current conflicting views: do biochars promote or suppress greenhouse gas emissions? In particular, the role of acetate, a product of organic matter degradation and substrate of methanogenesis, is poorly known. Here, we studied the effect of acetate concentrations on CH4 production by soils amended with biochar. Results show that biochar decreased CH4 release at low acetate concentration, below 0.2 mM. Gompertz modeling reveals that CH4 production rate can be reduced by up to 26.2% by biochar application. In apparent conflict, results show also that biochar stimulated methanogenesis at higher acetate concentrations, above 2 mM. Moreover, the application of CH3F, an inhibitor of acetoclastic methanogenesis, demonstrated that biochar mildly strengthened acetoclastic methanogenesis, thus confirming that biochar favors methane production. 13C isotope analysis demonstrated that CH4 is derived from direct acetate cleavage when the methanogenic substrate, e.g., acetate, was relatively abundant. Data from 16S rRNA sequencing suggest that CH4 is produced by the metabolism of Methanosarcinaceae. This work provides extra perspective that promotion or suppression of CH4 release by biochar may depend on acetate concentration in terrestrial methanogenic environments.

Reversibility of hydrolysis inhibition at high hydrogen partial pressure in dry anaerobic digestion processes fed with wheat straw and inoculated with anaerobic granular sludge

In dry anaerobic digestion (AD), methanogenic performances are lowered by high solid contents. Low performances are often caused by a decrease of the gas-liquid transfer kinetics leading to local accumulation of inhibitory by-products. Hydrogen was previously identified as an inhibitor of hydrolytic and acetogenic microbial activities in dry AD. CO2 is also generated but its impact on the microbial activity remains unknown. In this study, the reversibility of dry AD inhibition at high H2 partial pressure (PH2 of 1 bar) was investigated by adding CO2 (400 mbars) after 11 and 18 days of methanogenesis inhibition, in an AD process operated at 25% TS, using wheat straw as substrate and inoculated with anaerobic granular sludge. As soon as CO2 was added, the methanogenic activity rapidly recovered within 3 days, from 0.41 ± 0.1 to 3.77 ± 0.8 and then 2.25 ± 0.3, likely through the hydrogenotrophic pathway followed by the acetoclastic pathway, respectively. This result was confirmed by the high abundance of Methanomicrobiales (83%) and the emergence of Methanosarcinales sp (up to 17%) within the methanogenic community. Furthermore, the recovery kinetics were impacted by the duration of the inhibition period suggesting a different impact of the high PH2 on hydrogenotrophic and acetoclastic methanogens.

Improved hydrogen production in the single-chamber microbial electrolysis cell with inhibition of methanogenesis under alkaline conditions.

The aim of this study was to investigate hydrogen production enhanced by methanogenesis inhibition in the single-chamber microbial electrolysis cell (MEC) under alkaline conditions. With 50 mM bicarbonate buffer and 1 g L−1 acetate, the MEC was tested at pH = 8.5, 9.5, 10.5, and 11.2, respectively, within 124 d operation. Effective methanogenesis inhibition in the MEC increased with pH from 8.5 to 11.2. At pH 11.2, Methanobacteriaceae reached the lowest absolute quantity (i.e., biomass and mcrA gene copy number of methanogens) within the microbial community in the cathodic biofilm among the pH values. Under the alkaline conditions, a hydrogen percentage of 85–90% and a methane percentage < 15% were achieved within 25 cycles (50 d) of operation. The maximum current density in the MEC reached 83.7 ± 1.5 A m−3 with the average electrical recovery of 171 ± 18% and overall energy recovery of 72 ± 3%. The excellent performance of the MEC at pH = 11.2 was attributed to the low abundance of methanogens within the cathodic biofilm (2.23 ± 0.46 copy per cm2), low cathodic biomass (0.12 ± 0.01 mg protein per g), and low anode potential (−0.228 mV vs. saturated calomel electrode). Results from this study should be valuable to expand applications of the MEC with methanogenesis inhibition in alkaline wastewater treatment.

Iron-containing clay and hematite iron ore in slurry-phase anaerobic digestion of chicken manure

It is shown in this review that addition of clay minerals and hematite iron ore can significantly enhance anaerobic digestion of chicken manure. Liquid-phase anaerobic digestion of chicken manure consumes a lot of fresh water and energy to keep waste as a suspension. Meanwhile, anaerobic digestion of chicken manure in clay slurry without stirring could minimize energy and water consumption because the initial acceptable content of organic solids can be increased. For example, this content can be increased from 5% (w v-1) in suspension of chicken manure for liquidphase anaerobic digestion up to 15% (w v-1) in the slurry of chicken manure for slurry-phase anaerobic digestion than can save up to 13.3 L of water per kilogram of dry organic solids. The slurry-phase anaerobic digestion of nitrogen-, sulphur-, and fat-containing organic wastes can be enhanced using microbial reduction of Fe(Ⅲ) in clay or in hematite iron ore. This is due to adsorption or precipitation of such inhibitors of microbial acidogenesis and methanogenesis as ammonium, sulphide, long-chain fatty acids, humic and fulvic acids with clay or ferrous ions. For example, maximum concentration of ammonium decreased from 11.4 g L-1 during liquid-phase anaerobic digestion to 1.4 g L-1 during slurry-phase process due to adsorption of ammonium ions on clay. Addition of iron-containing clay to slurry-phase anaerobic reactor removed dissolved sulphide totally due to its precipitation with ferrous ions that are produced by bioreduction of Fe(Ⅲ) in clay. Slurry-phase anaerobic digestion enhanced with bioreduction of Fe(Ⅲ) minerals is also more effective process in terms of environmental safety than widely used liquid-phase anaerobic digestion because of an absence of water supply and wastewater effluent.

Effects of nanoscale zero valent iron (nZVI) concentration on the biochemical conversion of gaseous carbon dioxide (CO2) into methane (CH4)

This study presents the effects of nanoscale zero valent iron (nZVI) concentration on the biomethanation of gaseous CO2. During anaerobic batch experiment with 9 times injection of CO2, the CO2 concentration in the headspace rapidly decreased by dissolution. Then, when nZVI was added at 6.25 and 12.5 g/L, the dissolved CO2 was biochemically transformed into CH4 at a maximum production rate of 2.38 and 3.93 μmol/hr, respectively. Biomethanation at these two nZVI concentrations continued until the end of experiment. In spite of more H2 evolution by nZVI at 25 g/L, biomethanation did not occur, due to the significant inhibition of methanogenesis by nZVI. As the nZVI concentration increased, relative abundance of the hydrogenotrophic methanogens, especially Methanobacteriales, increased. However, at 25 g/L of nZVI concentration, acetic acid was accumulated and the relative abundance of Clostridium became predominant, indicating that homoacetogenesis was superior over methanogenesis.

Selective inhibition of methanogenesis by acetylene in single chamber microbial electrolysis cells

Microbial electrolysis cells (MECs) for hydrogen production exhibit great advantages over many other biohydrogen production techniques in terms of versatility of substrate and hydrogen yield. However, hydrogen and acetate scavenging by methanogens puts forward a great challenge to the application of single chamber MECs when using mixed culture. In this study, we investigated the feasibility of using acetylene, a low-cost fuel and chemical building block, to selectively inhibit methanogenesis in single chamber MECs. Results demonstrate that the periodical injection of low concentration acetylene (1% and 5%) can successfully inhibit methanogenesis in MECs using both acetate and glucose as substrates. Current generation by exoelectrogens and the syntrophy between fermentative bacteria and exoelectrogens, however, were not negatively affected. Compared with the classic methanogen inhibitor, 2-Bromoethanesulfonate (BES), the low concentration acetylene demonstrates superior effectiveness in MECs. These results demonstrate the great potential of using acetylene as a cost-effective inhibitor against methanogenesis in MECs.

Sawdust-Derived Biochar Much Mitigates VFAs Accumulation and Improves Microbial Activities To Enhance Methane Production in Thermophilic Anaerobic Digestion

Sawdust-derived biochar (SDBC) was added to an anaerobic digester at 15g/L for thermophilic codigestion under semicontinuous operation for more than 130 days. With a stepwise increase of organic loading rate (OLR) from 1.6 to 5.4 gVS/L·d–1, steady CH4 yields achieved between 462.3 and 500.1 mL/gVS. In contrast, for the control digester (without biochar addition) and another digester added with sewage sludge-derived biochar (SSBC), a steady working condition could only be maintained for about 80 days with OLR and CH4 yields up to 2.7 gVS/L·d–1 and 322.3–337.9 mL/gVS, respectively. The total volatile fatty acids (VFAs) accumulation up to about 30gCOD/L tended to be the threshold to restrain steady CH4 production, but this occurred much earlier for the control and SSBC digesters at much lower OLR. By batch experiments of digestion in a methanogenesis inhibition condition and with propionate or butyrate as the sole substrate, it was found that with SDBC addition, the substrate was oxidized steadily in the 40-...

Humic acid inhibition of hydrolysis and methanogenesis with different anaerobic inocula

There is increasing evidence that humic acid (HA) is hampering the performance of anaerobic digesters treating animal manures and thermally-hydrolysed waste activated sludge. In the present study, HA inhibition and inhibition resilience was examined for hydrolysis (carbohydrate and protein) and acetotrophic methanogenesis with four distinct full-scale anaerobic inocula. The aim was to further understand HA inhibition and to explore potential relationships between microbial factors and inhibition resilience. For two of the four tested inocula, cellulose degradation showed a start-up delay that lengthened as HA concentration increased from 0 to 2 g L−1. This inhibition was reversible because, after the initial delay, subsequent hydrolysis rates and methane yields were not significantly influenced by HA concentration. Cellulose hydrolysis results at HA concentrations below 2 g L−1 support a threshold inhibition mechanism, i.e. HA complexes with hydrolytic enzymes preventing them from binding with cellulose, but once all the HA had been complexed, enzymes subsequently released are free to bind with cellulose. Inocula with higher cellulose hydrolytic activity were less affected by HA inhibition, suggesting a potential link between HA inhibition resilience and microbial activity. However, above 5 gHA L−1, cellulose hydrolysis rates decreased with increasing HA concentration; indicating that the mechanisms of inhibition may change depending on some threshold HA concentration. Protein hydrolysis and acetotrophic methanogenesis were less susceptible to HA inhibition than cellulose hydrolysis, since signs of inhibition were only observed above 5 gHA L−1. Acetotrophic methanogenesis was partially inhibited at 10 gHA L−1 and completely inhibited at 20 gHA L−1. These results further support that HA inhibition is selective towards particular enzymes.

Rice cultivation reduces methane emissions in high-emitting paddies

Background: Rice is typically understood to enhance methane emissions from paddy fields. However, rice actually has two separate functions related to methane: i) emission enhancement, such as by providing emission pathways (aerenchyma) and methanogenetic substrates; and ii) emission suppression by providing oxygen pathways, which suppress methanogenesis or enhance methane oxidation. The overall role of rice is thus determined by the balance between its enhancing and suppressing functions. Although existing studies have suggested that rice enhances total methane emissions, we aimed to demonstrate that the balance between rice’s emitting and suppressing functions changes according to overall methane emission levels, which have quite a large range (16‍–500 kg methane ha−1 crop−1). Methods: Using PVC chambers, we compared methane emissions emitted by rice paddy fields with and without rice plants in rice fields in the Mekong Delta, Vietnam. Samples were analyzed by gas chromatograph. Results: We found high overall methane emission levels and our results indicated that rice in fact suppressed methane emissions under these conditions. Emission reductions increased with the growth of rice, up to 60% of emission rate at the maximum tillering stage, then decreased to 20% after the heading stage, and finally recovering back to 60%. Discussion: It is known that methane is emitted by ebullition when the emission level is high, and methane emission reductions in rice-planted fields are thought to be due to oxidation and methanogenesis suppression. However, although many studies have found that the contribution of soil organic matter to methanogenesis is small, our results suggested that methanogenesis depended mainly on soil organic matter accumulated from past crops. The higher the methane emission level, the lower the contribution of rice-providing substrate. Conclusion: As a result, during the growing season, rice enhanced methane emissions in low-emission paddy fields but suppressed methane emissions in high-emission paddy fields.

Dynamic isotope equations for 13CH4 and 13CO2 describing methane formation with a focus on the effect of anaerobic respiration in sediments of some tropical lakes

The production of CO2 during sediment decomposition in field and laboratory incubations is often reported to be higher than that of CH4. We present a mathematical description of cellulose conversion into methane and carbon dioxide in the anoxic sediments of tropical Ladario and Belmont Lakes, which were investigated before. The processes of anaerobic respiration and acidogenesis competing for cellulose monomer, as well as the processes of anaerobic respiration, acetoclastic methanogenesis, and syntrophic acetate oxidation, competing for acetate, are considered. The gaseous and dissolved H2, CO2, and CH4 are taken into account in dynamic equations for total 12C+13C and 13C carbon in CH4 and CO2. Considering the amounts of CH4 and CO2 produced during the batch tests and changes in their carbon isotope values, modelling based on balances of summary total 12C+13C and 13C carbon is used to adequately describe the experimental data on sediment methanization. The high CO2:CH4 ratio with a delay in methane production observed in the batch experiments is interpreted by the model as due to an initial Fe3+ reduction. The model is validated by describing the system's dynamics under strong inhibition of acetoclastic methanogenesis by methyl fluoride. For comparison, the model is used to show a standard pathway of cellulose methanization in the tropical Anzol de Ouro Lake with a 1:1 ratio of produced CO2 to CH4, in conditions in which anaerobic respiration was proved to be insignificant.

Coupled methane and nitrous oxide biotransformation in freshwater wetland sediment microcosms

Anaerobic oxidation of methane (AOM) coupled to denitrification is becoming the focus of scientific inquiry due to its potential contribution to global carbon and nitrogen cycles. AOM has been previously reported to proceed with nitrate (NO3−) or nitrite (NO2−). However, little research has been conducted on the simultaneous use of methane (CH4) and nitrous oxide (N2O). Here, coupled CH4 and N2O biotransformation in a freshwater wetland sediment was obtained in a 7-day anaerobic sediment incubation assay. The significant CO2 accumulation and decrease of CH4 emission in sediment microcosms was attributed to two mechanisms: inhibition of methanogenesis and N2O-dependent AOM. To further confirm the coupled CH4 and N2O transformation, a 13C-labelled stable isotope tracer assay after anaerobic incubation was conducted with N2O and/or CH4 amendments. The N2O-dependent AOM rate was 3.41 ± 0.13 nmol CO2 g−1 dry sediment·day−1. According to metagenomic analysis, addition of N2O stimulated AOM by increasing the activity and abundance of methanotrophic bacteria and by increasing enzymatic activities in the electron transport chain. Based on these results, we propose coupled CH4 and N2O biotransformation in the sediment microcosms for the first time, carried out by unidentified methanotroph(s) via intra‑oxygen produced in the presence of N2O. Such a process has the potential to reduce the emission of two highly potent greenhouse gases and makes a significant contribution to the link of global carbon and nitrogen cycles in anoxic environments.

3-NOP vs. Halogenated Compound: Methane Production, Ruminal Fermentation and Microbial Community Response in Forage Fed Cattle.

The aim of this study was to investigate the effects of 3-nitrooxypropanol (3-NOP) and chloroform on methane (CH4) and H2 production, ruminal metabolites and microbial community structure in cattle fed a tropical forage diet. Eight rumen-fistulated steers were fed a roughage hay diet (Rhodes grass; Chloris gayana) for 31 days (control period). Four animals received the antimethanogenic compound chloroform (1.6 g chloroform–cyclodextrin/100 kg live weight (LW)) while the other four received 3-NOP (2.5 g 3-NOP/animal/day) for 21 days. Methane decrease compared with control period was similar for both treatments (30–38%) with no differences for expelled H2 between controls and treatments. Daily weight gain (DWG) was significantly increased when animals were treated with 3-NOP compared with chloroform and control. Regarding the ruminal fermentation parameters increases in ammonia, acetate and branched chain fatty acids were observed with both compounds compared with the controls. Also, methylamines, alcohols and dimethyl sulfone (DMSO2) concentrations were significantly increased with the treatments compared with control, being greater with 3-NOP. The rumen microbial analyses revealed a similar profile for both treatments, with a shift in operational taxonomic units (OTUs) assigned to the Prevotellaceae and Campylobacteraceae family. Moreover, major archaeal OTUs associated with Methanobrevibacter and Methanosphaera were significantly affected to varying extents based on the inhibitory treatments compared to the control. The abundance of the Methanobrevibacter spp. was decreased by 3-NOP and chloroform, while the Methanomassiliicoccaceae family was inhibited only by 3-NOP. The results suggest that despite the specific mode of action of 3-NOP on methanogens, inhibition of methanogenesis by both compounds resulted in similar responses in metabolism and microbial community structure in the rumen. We hypothesized that these changes were driven by the redirection of metabolic hydrogen ([H]) by both treatments. Therefore results from previous publications using chloroform as an inhibitor of methanogenesis may be useful in predicting ruminal microbiota and fermentation responses to 3-NOP.

Inhibition of Rumen Methanogenesis and Ruminant Productivity: A Meta-Analysis.

Methane (CH4) formed in the rumen and released to the atmosphere constitutes an energy inefficiency to ruminant production. Redirecting energy in CH4 to fermentation products with a nutritional value to the host animal could increase ruminant productivity and stimulate the adoption of CH4-suppressing strategies. The hypothesis of this research was that inhibiting CH4 formation in the rumen is associated with greater ruminant productivity. The primary objective of this meta-analysis was to evaluate how inhibiting rumen methanogenesis relates with the efficiencies of milk production and growth and fattening. A systematic review of peer-reviewed studies in which rumen methanogenesis was inhibited with chemical compounds was conducted. Experiments were clustered based on research center, year of publication, experimental design, feeding regime, type of animal, production response, inhibitor of CH4 production, and method of CH4 measurement. Response variables were regressed against the random experiment effect nested in its cluster, the random effect of the cluster, the linear and quadratic effects of CH4 production, and the random interaction between CH4 production and the experiment nested in the cluster. When applicable, responses were adjusted by intake of different nutrients included as regressors. Inhibiting rumen methanogenesis tended to associate positively with milk production efficiency, although the relationship was influenced by individual experiments. Likewise, a positive relationship between methanogenesis inhibition and growth and fattening efficiency depended on the inclusion and weighting of individual experiments. Inhibiting rumen methanogenesis negatively associated with dry matter intake. Interpretation of the effects of inhibiting methanogenesis on productivity is limited by the availability of experiments simultaneously reporting energy losses in feces, H2, urine and heat production, as well as net energy partition. It is concluded that inhibiting rumen methanogenesis has not consistently translated into greater animal productivity, and more animal performance experiments are necessary to better characterize the relationships between animal productivity and methanogenesis inhibition in the rumen. A more complete understanding of changes in the flows of nutrients caused by inhibiting rumen methanogenesis and their effect on intake also seems necessary to effectively re-channel energy gained from CH4 suppression toward consistent gains in productivity.

Modelling the specific pathway of CH4 and CO2 formation using carbon isotope fractionation: an example for a boreal mesotrophic fen

ABSTRACTWe described mathematically the process of peat methanization in a boreal mesotrophic fen. Gaseous and dissolved CH4 and CO2 as well as their δ13C signatures were considered in the dynamic equations for incubation bottles. In accordance with the model, acetate, H2, and CO2 were produced during cellulose hydrolysis and acidogenesis. 13C/12C in CO2 was a key variable reflecting dynamic changes in the rates of cellulose hydrolysis and acidogenesis, acetoclastic and hydrogenotrophic methanogenesis. As CO2 is the substrate in hydrogenotrophic methanogenesis, δ13C–CO2 increased from the start till the dissolved hydrogen concentration became very low. Thereafter, the rate of acetoclastic methanogenesis with the significant current acetate concentration dominated over the rate of hydrogenotrophic methanogenesis leading to the decreasing δ13C–CO2 and the increasing δ13C–CH4. The model was validated by describing the system’s dynamics under strong and weak inhibition of acetoclastic and hydrogenotrophic methanogenesis by methyl fluoride, respectively. During peat methanization at the lowered temperature of 10 °C, the processes of hydrogenotrophic methanogenesis and homoacetogenesis competing for H2 may occur. However, based on dynamics of the carbon isotope signatures, especially on dynamics of δ13C–CO2, the model showed no significant contribution of homoacetogens in peat methanization.

Free acetic acid as the key factor for the inhibition of hydrogenotrophic methanogenesis in mesophilic mixed culture fermentation

The inhibition of acetate under acidic pH is an ideal way to reduce methanogenesis in mesophilic mixed culture fermentation (MCF). However, the effects of acetate concentration and acidic pH on methanogenesis remain unclear. Besides, although hydrogenotrophic methanogens can be suitable targets in MCF, they are generally ignored. Therefore, we intentionally enriched hydrogenotrophic methanogens and found that free acetic acid (FAA, x) concentration and specific methanogenic activity (SMA, y) were correlated according to the equation: y = 0.86 × 0.31/(0.31 + x) (R2 = 0.909). The SMA was decreased by 50% and 90% at the FAA concentrations of 0.31 and 2.36 g/L, respectively. The coenzyme M concentration and relative electron transport activity agreed well with the FAA concentration. Moreover, the methanogenic activity could not be recovered when the FAA concentration exceeded 0.81 g/L. These findings indicated that neither acetate nor acidic pH, but FAA was the key factor to inhibit methanogenesis in MCF.

Climate-driven shifts in sediment chemistry enhance methane production in northern lakes

Freshwater ecosystems are a major source of methane (CH4), contributing 0.65 Pg (in CO2 equivalents) yr−1 towards global carbon emissions and offsetting ~25% of the terrestrial carbon sink. Most freshwater CH4 emissions come from littoral sediments, where large quantities of plant material are decomposed. Climate change is predicted to shift plant community composition, and thus change the quality of inputs into detrital food webs, with the potential to affect CH4 production. Here we find that variation in phenol availability from decomposing organic matter underlies large differences in CH4 production in lake sediments. Production is at least 400-times higher from sediments composed of macrophyte litter compared to terrestrial sources because of inhibition of methanogenesis by phenol leachates. Our results now suggest that earth system models and carbon budgets should consider the effects of plant communities on sediment chemistry and ultimately CH4 emissions at a global scale.

Conductive Particles Enable Syntrophic Acetate Oxidation between Geobacter and Methanosarcina from Coastal Sediments

ABSTRACTCoastal sediments are rich in conductive particles, possibly affecting microbial processes for which acetate is a central intermediate. In the methanogenic zone, acetate is consumed by methanogens and/or syntrophic acetate-oxidizing (SAO) consortia. SAO consortia live under extreme thermodynamic pressure, and their survival depends on successful partnership. Here, we demonstrate that conductive particles enable the partnership between SAO bacteria (i.e., Geobacter spp.) and methanogens (Methanosarcina spp.) from the coastal sediments of the Bothnian Bay of the Baltic Sea. Baltic methanogenic sediments were rich in conductive minerals, had an apparent isotopic fractionation characteristic of CO2-reductive methanogenesis, and were inhabited by Geobacter and Methanosarcina. As long as conductive particles were delivered, Geobacter and Methanosarcina persisted, whereas exclusion of conductive particles led to the extinction of Geobacter. Baltic Geobacter did not establish a direct electric contact with Methanosarcina, necessitating conductive particles as electrical conduits. Within SAO consortia, Geobacter was an efficient [13C]acetate utilizer, accounting for 82% of the assimilation and 27% of the breakdown of acetate. Geobacter benefits from the association with the methanogen, because in the absence of an electron acceptor it can use Methanosarcina as a terminal electron sink. Consequently, inhibition of methanogenesis constrained the SAO activity of Geobacter as well. A potential benefit for Methanosarcina partnering with Geobacter is that together they competitively exclude acetoclastic methanogens like Methanothrix from an environment rich in conductive particles. Conductive particle-mediated SAO could explain the abundance of acetate oxidizers like Geobacter in the methanogenic zone of sediments where no electron acceptors other than CO2 are available.