Methane production and sulfate reduction in two Appalachian peatlands

Anaerobic carbon mineralization was evaluated over a 1-year period in two Sphagnum-dominated peatlands, Big Run Bog, West Virginia, and Buckle's Bog, Maryland. In the top 35 cm of peat, mean rates of methane production, anaerobic carbon dioxide production, and sulfate reduction at Big Run Bog were 63,406 and 146 mol L^-1 d^-1, respectively, and at Buckle's Bog were 18, 486 and 104 mol L^-1 d^-1. Annual anaerobic carbon mineralization to methane and carbon dioxide at Big Run Bog and Buckle's Bog was 52.8 and 57.2 mol m^-2, respectively. Rates of methane production were similar to rates reported for other freshwater peatlands, but methane production accounted for only 11.7 and 2.8%, respectively, of the total anaerobic carbon mineralization at these two sites. Carbon dioxide production, resulting substantially from sulfate reduction, dominated anaerobic carbon mineralization. Considerable sulfate reduction despite low instantaneous dissolved sulfate concentrations (typically < 300 mol L^-1 of substrate) was apparently fueled by oxidation and rapid turnover of the reduced inorganic sulfur pool.The coincidence of high sulfate inputs to the Big Run Bog and Buckle's Bog watersheds through acid precipitation with the unexpected importance of sulfate reduction leads us to suggest a new hypothesis: peatlands not receiving high sulfate loading should exhibit low rates of anaerobic decomposition, and a predominance of methane production over sulfate reduction; however, if such peatlands become subjected to high rates of sulfur deposition, sulfate reduction may be enhanced as an anaerobic mineralization pathway with attendant effects on carbon balance and peat accumulation.     

Methane emission from feather moss stands

Data from remote sensing and Eddy towers indicate that forests are not always net sinks for atmospheric CH₄. However, studies describing specific sources within forests and functional analysis of microorganisms on sites with CH₄ turnover are scarce. Feather moss stands were considered to be net sinks for carbon dioxide, but received little attention to their role in CH₄ cycling. Therefore, we investigated methanogenic rates and pathways together with the methanogenic microbial community composition in feather moss stands from temperate and boreal forests. Potential rates of CH₄ emission from intact moss stands (n = 60) under aerobic conditions ranged between 19 and 133 pmol CH₄ h^?1 gdw^?1. Temperature and water content positively influenced CH₄ emission. Methanogenic potentials determined under N₂ atmosphere in darkness ranged between 22 and 157 pmol CH₄ h^?1 gdw^?1. Methane production was strongly inhibited by bromoethane sulfonate or chloroform, showing that CH₄ was of microbial origin. The moss samples tested contained fluorescent microbial cells and between 10⁴ and 10⁵ copies per gram dry weight moss of the mcrA gene coding for a subunit of the methyl CoM reductase. Archaeal 16S rRNA and mcrA gene sequences in the moss stands were characteristic for the archaeal families Methanobacteriaceae and Methanosarcinaceae. The potential methanogenic rates were similar in incubations with and without methyl fluoride, indicating that the CH₄ was produced by the hydrogenotrophic rather than aceticlastic pathway. Consistently, the CH₄ produced was depleted in ¹³C in comparison with the moss biomass carbon and acetate accumulated to rather high concentrations (3–62 mM). The δ¹³C of acetate was similar to that of the moss biomass, indicating acetate production by fermentation. Our study showed that the feather moss stands contained active methanogenic microbial communities producing CH₄ by hydrogenotrophic methanogenesis and causing net emission of CH₄ under ambient conditions, albeit at low rates.     

Methane production and methane consumption: a review of processes underlying wetland methane fluxes

Potential rates of both methane production and methane consumptionvary over three orders of magnitude and their distribution is skew.These rates are weakly correlated with ecosystem type, incubationtemperature, in situ aeration, latitude, depth and distanceto oxic/anoxic interface. Anaerobic carbon mineralisation is amajor control of methane production. The large range in anaerobicCH₄:CO₂ production rates indicate that a largepart of the anaerobically mineralised carbon is used for reduction ofelectron acceptors, and, hence, is not available for methanogenesis.Consequently, cycling of electron acceptors needs to be studied tounderstand methane production. Methane and oxygen half saturationconstants for methane oxidation vary about one order of magnitude.Potential methane oxidation seems to be correlated withmethanotrophic biomass. Therefore, variation in potential methaneoxidation could be related to site characteristics with a model ofmethanotrophic biomass.     

Methane production by the sulfate-reducing bacteriumDesulfosarcina variabilis

The sulfate-reducing bacteriumDesulfosarcina variabilis VKM B-1694 was found to produce up to 1.62 Ώmol methane per mg protein when grown on different substrates. The role of methanogenesis and the physicochemical factors determining this process in sulfate-reducing bacteria are discussed.     

Mechanisms for hydrogen production by different bacteria during mixed-acid and photo-fermentation and perspectives of hydrogen production biotechnology

H₂ has a great potential as an ecologically-clean, renewable and capable fuel. It can be mainly produced via hydrogenases (Hyd) by different bacteria, especially Escherichia coli and Rhodobacter sphaeroides. The operation direction and activity of multiple Hyd enzymes in E. coli during mixed-acid fermentation might determine H₂ production; some metabolic cross-talk between Hyd enzymes is proposed. Manipulating the activity of different Hyd enzymes is an effective way to enhance H₂ production by E. coli in biotechnology. Moreover, a novel approach would be the use of glycerol as feedstock in fermentation processes leading to H₂ production. Mixed carbon (sugar and glycerol) utilization studies enlarge the kind of organic wastes used in biotechnology. During photo-fermentation under limited nitrogen conditions, H₂ production by Rh. sphaeroides is observed when carbon and nitrogen sources are supplemented. The relationship of H₂ production with H⁺ transport across the membrane and membrane-associated ATPase activity is shown. On the other hand, combination of carbon sources (succinate, malate) with different nitrogen sources (yeast extract, glutamate, glycine) as well as different metal (Fe, Ni, Mg) ions might regulate H₂ production. All these can enhance H₂ production yield by Rh. sphaeroides in biotechnology Finally, two of these bacteria might be combined to develop and consequently to optimize two stages of H₂ production biotechnology with high efficiency transformation of different organic sources.     

Hydrogen emission by three wood-feeding subterranean termite species (Isoptera: Rhinotermitidae): Production and characteristics

Abstract Hydrogen emission by wood-feeding termites, Coptotermes formosanus, Reticulitermes flavipes and Reticulitermes virginicus, was investigated upon a cellulosic substrate as their food source. The emission rates among the three species tested were significantly different and R. virginicus demonstrated the greatest H₂ emission at 4.78 ± 0.15 μmol/h/g body weight. In a sealed test apparatus, H₂ emission for each termite species showed a quick increase at the initial incubation hours (3–6 h), followed by a slower growth, possibly due to the feedback inhibition by gas accumulation. Further investigation revealed that continuous H₂ emission could be maintained by reducing the H₂ partial pressure in the sealed container. The bioconversion of cellulose to molecular H₂ by the subterranean termites tested could reach as high as 3 858 ± 294 μmol/g cellulose, suggesting that the termite gut system is unique and efficient in H₂ conversion from cellulosic substrate.     

Methane production and diurnal variation measured in dairy cows and predicted from fermentation pattern and nutrient or carbon flow

Many feeding trials have been conducted to quantify enteric methane (CH₄) production in ruminants. Although a relationship between diet composition, rumen fermentation and CH₄ production is generally accepted, the efforts to quantify this relationship within the same experiment remain scarce. In the present study, a data set was compiled from the results of three intensive respiration chamber trials with lactating rumen and intestinal fistulated Holstein cows, including measurements of rumen and intestinal digestion, rumen fermentation parameters and CH₄ production. Two approaches were used to calculate CH₄ from observations: (1) a rumen organic matter (OM) balance was derived from OM intake and duodenal organic matter flow (DOM) distinguishing various nutrients and (2) a rumen carbon balance was derived from carbon intake and duodenal carbon flow (DCARB). Duodenal flow was corrected for endogenous matter, and contribution of fermentation in the large intestine was accounted for. Hydrogen (H₂) arising from fermentation was calculated using the fermentation pattern measured in rumen fluid. CH₄ was calculated from H₂ production corrected for H₂ use with biohydrogenation of fatty acids. The DOM model overestimated CH₄/kg dry matter intake (DMI) by 6.1% (R²=0.36) and the DCARB model underestimated CH₄/kg DMI by 0.4% (R²=0.43). A stepwise regression of the difference between measured and calculated daily CH₄ production was conducted to examine explanations for the deviance. Dietary carbohydrate composition and rumen carbohydrate digestion were the main sources of inaccuracies for both models. Furthermore, differences were related to rumen ammonia concentration with the DOM model and to rumen pH and dietary fat with the DCARB model. Adding these parameters to the models and performing a multiple regression against observed daily CH₄ production resulted in R² of 0.66 and 0.72 for DOM and DCARB models, respectively. The diurnal pattern of CH₄ production followed that of rumen volatile fatty acid (VFA) concentration and the CH₄ to CO₂ production ratio, but was inverse to rumen pH and the rumen hydrogen balance calculated from 4×(acetate+butyrate)/2×(propionate+valerate). In conclusion, the amount of feed fermented was the most important factor determining variations in CH₄ production between animals, diets and during the day. Interactions between feed components, VFA absorption rates and variation between animals seemed to be factors that were complicating the accurate prediction of CH₄. Using a ruminal carbon balance appeared to predict CH₄ production just as well as calculations based on rumen digestion of individual nutrients.     

Methane production in meromictic Ace Lake,Antarctica

Methane occurred in the monimolimnion, at depths greater than 11 m, of an antarctic meromictic lake, Ace Lake (depth 24.7 m). Although the water of the lake was of approximate marine salinity, bottom waters were depleted in sulfate (less than 1 mmol 1^–1). The temperature of the bottom waters of the lake were constantly between 1 °C and 2 °C. Rates of methanogenesis from ¹⁴C-labelled precursors (bicarbonate, formate and acetate) were determined in time course experiments with the detection of ¹⁴CH₄ produced by a gas chromatography-gas proportional counting system. Rates of ¹⁴CH₄ production were difficult to determine as the reactions were always near our limit of detection.Reliable determinations of rates of methanogenesis at some depths using some precursors were obtained, the fastest rate being 2.5 µmol kg^–1 day^–1 at depth 20 m. Assuming constant rates of methanogenesis with time, this would equate to a turnover of methane in the lake every two years.The slow rate of methanogenesis suggests that the methanogens in Ace Lake may be working at well below their optimum temperature although definitive statements regarding the presence of psychrophilic methanogens in this antarctic lake must await isolation attempts or longer field studies using alternative methodologies.     

Methane emissions from rice microcosms: The balance of production, accumulation and oxidation

In rice microcosms (Oryza sativa, var. Roma, type japonica),CH₄ emission, CH₄ production, CH₄oxidation and CH₄ accumulation were measured over an entirevegetation period. Diffusive CH₄ emission was measured inclosed chambers, CH₄ production was measured in soil samples,CH₄ oxidation was determined from the difference between oxicand anoxic emissions, and CH₄ accumulation was measured byanalysis of porewater and gas bubbles. The sum of diffusiveCH₄ emission, CH₄ oxidation, andCH₄ accumulation was only 60% of the cumulativeCH₄ production. The two values diverged during the first 50days (vegetative phase) and then again during the last 50 days (latereproductive phase and senescence) of the 150 day vegetation period. Duringthe period of day 50–100 (early reproductive phase/flowering), theprocesses were balanced. Most likely, gas bubbles and diffusion limitationare responsible for the divergence in the early and late phases. The effectof rice on CH₄ production rates and CH₄concentrations was studied by measuring these processes also in unplantedmicrocosms. Presence of rice plants lowered the CH₄concentrations, but had no net effect on the CH₄ productionrates.     

Modeling alginate encapsulation system for biological hydrogen production

Wastewater treatment using encapsulated biomass is a promising approach for high-rate resource recovery. Encapsulation matrices can be customized to achieve desired biomass retention and mass transport performance. This, in turn, facilitates treatment of different waste streams. In this study, a model was developed to describe calcium-alginate beads encapsulating hydrogen-producing biomass, with the goal of enabling appropriate a priori customization of the system. The model was based on a classic diffusion-reaction model, but also included the growth of encapsulated biomass and product inhibition. Experimental data were used to verify the model, which accurately described the effect of hydraulic retention time, bead size, and feed concentration on resource (hydrogen) recovery from brewery wastewater. Sensitivity analyses revealed that the hydrogen production rate was insensitive to substrate diffusivity and bead size, but sensitive to the substrate partition coefficient, initial encapsulated biomass concentration, and the total volume of beads in the reactor, demonstrating that this system was growth-limited rather than diffusion-limited under the tested conditions. Because the model quantifies the relationship between the hydrogen production rate and various input and operating parameters, it should be possible to extend the model to determine the most cost-effective system for optimal performance with a given waste stream.     

Performance characteristics of a two-stage dark fermentative system producing hydrogen and methane continuously

The performance of a mesophilic two-stage system generating hydrogen and methane continuously from sucrose (10-30 g/L) was investigated. A hydrogen-generating CSTR followed by an upflow anaerobic filter were both inoculated with anaerobically digested sewage sludge, and ORP, pH, gas output, %H(2), %CH(4) and %CO(2) monitored. pH was controlled with NaOH, KOH or Ca(OH)(2). Using NaOH as alkali with 10 g/L sucrose, yields of 1.62 +/- 0.2 mol H(2)/mol hexose added and 323 mL CH(4)/gCOD added to the hydrogen and methane reactors respectively were achieved. The overall chemical oxygen demand (COD) reduction was 92.6% with 0.90 +/- 0.1 g/L sodium and 316 +/- 40 mg/L residual acetate in the methane reactor. Operation at 20 g/L sucrose and NaOH as alkali led to impaired volatile fatty acid (VFA) degradation in the methane reactor with 2.23 +/- 0.2 g/L sodium, 1,885 mg/L residual acetate, a hydrogen yield of 1.47 +/- 0.1 mol/mol hexose added, a methane yield of 294 mL/gCOD added and an overall COD reduction of 83%. Using Ca(OH)(2) as alkali with 20 g/L sucrose gave a hydrogen yield of 1.29 +/- 0.3 mol/mol hexose added, a methane yield of 337 mL/gCOD added and improved the overall COD reduction to 91% with residual acetate concentrations of 522 +/- 87 mg/L. Operation at 30 g/L sucrose with Ca(OH)(2) gave poorer overall COD reduction (68%), a hydrogen yield of 1.47 +/- 0.2 mol/mol hexose added, a methane yield of 138 mL/gCOD added and residual acetate 7,343 +/- 715 mg/L. It was shown that sodium toxicity and overloading are important issues for successful anaerobic digestion of effluent from biohydrogen reactors in high rate systems.     

Surfactant-Induced hydrogen production in cyanobacteria

Addition of Tween 85 to aqueous suspensions of Anabaena variabilis induced photosynthetic evolution of hydrogen over a time span of several weeks: As much as 148 nmol H(2)/h . mg dry weight was produced in the first week by a suspension containing 4.2 mg dry weight of cells and 77 mM Tween 85. The chemical structure of Tween 85 was a necessary prerequisite for inducing hydrogen production, as compounds such as Tween 20, 60, and 80 had a quite different effect. There was a coupling between photosynthetic oxygen evolution and hydrogen evolution: Hydrogen evolution started to be effective only when oxygen evolution subdued. The presence of heterocysts in A. variabilis was also required for the Tween-induced hydrogen production. Based on these observations, possible mechanisms for the photosynthetic effect of Tween 85 are advanced and discussed. (c) 1993 John Wiley & Sons, Inc.     

Cyanobacterial hydrogen production

With the global attention and research now being focussed on looking for an alternative to fossil fuel, hydrogen is the hope of future. Cyanobacteria are highly promising microorganisms for biological photohydrogen production. The review highlights the advancement in the biology of cyanobacterial hydrogen production in recent years. It discusses the enzymes involved in hydrogen production, viz. hydrogenases and nitrogenases, various strategies developed by cyanobacteria to limit nitrogenase inactivation by atmospheric and photosynthetic O₂, different biochemical and physicochemical parameters influencing the commercial cyanobacterial hydrogen production and the methods opted by different researchers for eliminating them to obtain maximum and sustained hydrogen production. Integrating the existing knowledge, techniques and expertise available, much future improvement and progress can be made in the field. This revised version was published online in November 2006 with corrections to the Cover Date.     

Methane production capacities of different rice soils derived from inherent and exogenous substrates

Methane production rates were determined at weekly intervals during anaerobic incubation of eleven Philippine rice soils. The average production rates at 25 °C varied in a large range from 0.03 to 13.6 g CH_{4 g(d.w. soil)} ^-1d^-1. The development of methane production rates derived from inherent substrate allowed a grouping of soils in three classes: those with instantaneous development, those with a delay of approximately two weeks, and those with a suppression of methane production of more than eight weeks. Incubation at 30 and 35 °C increased production capacities of all soils, but the grouping of soils was still maintained. The Arrhenius equation provided a good fit for temperature effects on methane production capacities except for those soils with suppressed production. Acetate amendment strongly enhanced methane production rates and disintegrated the grouping. However, the efficiencies in converting acetate to methane differed among soils. Depending on the soil, 16.5–66.7% of the added acetate was utilized within five weeks incubation at 25 °C.Correlation analyses of methane production (over eight weeks) and physico-chemical soil parameters yielded significant correlations for the concentrations of organic carbon (R² = 0.42) and organic nitrogen (R² = 0.52). Correlation indices could substantially be enhanced by using the enriched fraction of organic carbon (R² = 0.94) and organic nitrogen (R² = 0.77), i.e. the differential between topsoil and subsoil concentrations of the respective compounds. The enriched organic material in the topsoil corresponds to the biologically active fraction and thus represents a good indicator of methane production derived from inherent substrate. The best indicators of the conversion rate of acetate in different soils were pH-value (R² = 0.56) and organic carbon content (R² = 0.52).Apparently, soil properties affect methane production through various pathways. Inherent organic substrate represents a considerable source of methane in some soils and is negligible in others. Likewise, soils also differ regarding the response to exogenous substrate. Both mechanisms yield in a distinct spatial variability of methane production in rice soils.     

Oxygen effects on methane production and oxidation in humid tropical forest soils

We investigated the effects of oxygen (O₂) concentration on methane (CH₄) production and oxidation in two humid tropical forests that differ in long‐term, time‐averaged soil O₂ concentrations. We identified sources and sinks of CH₄ through the analysis of soil gas concentrations, surface emissions, and carbon isotope measurements. Isotope mass balance models were used to calculate the fraction of CH₄ oxidized in situ. Complementary laboratory experiments were conducted to determine the effects of O₂ concentration on gross and net rates of methanogenesis. Field and laboratory experiments indicated that high levels of CH₄ production occurred in soils that contained between 9±1.1% and 19±0.2% O₂. For example, we observed CH₄ concentrations in excess of 3% in soils with 9±1.1% O₂. CH₄ emissions from the lower O₂ sites were high (22–101 nmol CH₄ m^?2 s^?1), and were equal in magnitude to CH₄ emissions from natural wetlands. During peak periods of CH₄ efflux, carbon dioxide (CO₂) emissions became enriched in ¹³C because of high methanogenic activity. Gross CH₄ production was probably greater than flux measurements indicated, as isotope mass balance calculations suggested that 48–78% of the CH₄ produced was oxidized prior to atmospheric egress. O₂ availability influenced CH₄ oxidation more strongly than methanogenesis. Gross CH₄ production was relatively insensitive to O₂ concentrations in laboratory experiments. In contrast, methanotrophic bacteria oxidized a greater fraction of total CH₄ production with increasing O₂ concentration, shifting the δ¹³C composition of CH₄ to values that were more positive. Isotopic measurements suggested that CO₂ was an important source of carbon for methanogenesis in humid forests. The δ¹³C value of methanogenesis was between ?84‰ and ?98‰, which is well within the range of CH₄ produced from CO₂ reduction, and considerably more depleted in ¹³C than CH₄ formed from acetate.     

Simultaneous hydrogen utilization and in situ biogas upgrading in an anaerobic reactor

The possibility of converting hydrogen to methane and simultaneous upgrading of biogas was investigated in both batch tests and fully mixed biogas reactor, simultaneously fed with manure and hydrogen. Batch experiments showed that hydrogen could be converted to methane by hydrogenotrophic methanogenesis with conversion of more than 90% of the consumed hydrogen to methane. The hydrogen consumption rates were affected by both (hydrogen partial pressure) and mixing intensity. Inhibition of propionate and butyrate degradation by hydrogen (1 atm) was only observed under high mixing intensity (shaking speed 300 rpm). Continuous addition of hydrogen (flow rate of 28.6 mL/(L/h)) to an anaerobic reactor fed with manure, showed that more than 80% of the hydrogen was utilized. The propionate and butyrate level in the reactor was not significantly affected by the hydrogen addition. The methane production rate of the reactor with H₂ addition was 22% higher, compared to the control reactor only fed with manure. The CO₂ content in the produced biogas was only 15%, while it was 38% in the control reactor. However, the addition of hydrogen resulted in increase of pH (from 8.0 to 8.3) due to the consumption of bicarbonate, which subsequently caused slight inhibition of methanogenesis. Biotechnol. Bioeng. 2012; 109:1088–1094. © 2011 Wiley Periodicals, Inc.     

Methane in West Siberia terrestrial seeps: Origin,transport, and metabolic pathways of production

The expansive plains of West Siberia contain globally significant carbon stocks, with Earth's most extensive peatland complex overlying the world's largest-known hydrocarbon basin. Numerous terrestrial methane seeps have recently been discovered on this landscape, located along the floodplains of the Ob and Irtysh Rivers in hotspots covering more than 2500 km². We articulated three hypotheses to explain the origin and migration pathways of methane within these seeps: (H1) uplift of Cretaceous-aged methane from deep petroleum reservoirs along faults and fractures, (H2) release of Oligocene-aged methane capped or trapped by degrading permafrost, and (H3) horizontal migration of Holocene-aged methane from surrounding peatlands. We tested these hypotheses using a range of geochemical tools on gas and water samples extracted from seeps, peatlands, and aquifers across the 120,000 km² study area. Seep-gas composition, radiocarbon age, and stable isotope fingerprints favor the peatland hypothesis of seep-methane origin (H3). Organic matter in raised bogs is the primary source of seep methane, but observed variability in stable isotope composition and concentration suggest production in two divergent biogeochemical settings that support distinct metabolic pathways of methanogenesis. Comparison of these parameters in raised bogs and seeps indicates that the first is bogs, via CO₂ reduction methanogenesis. The second setting is likely groundwater, where dissolved organic carbon from bogs is degraded via chemolithotrophic acetogenesis followed by acetate fermentation methanogenesis. Our findings highlight the importance of methane lateral migration in West Siberia's bog-dominated landscapes via intimate groundwater connections. The same phenomenon could occur in similar landscapes across the boreal-taiga biome, thereby making groundwater-fed rivers and springs potent methane sources.     

Influence of Feed Components on Symbiotic Bacterial Community Structure in the Gut of the Wood-Feeding Higher Termite Nasutitermes takasagoensis

The influence of carbon sources on bacterial community structure in the gut of the wood-feeding higher termite Nasutitermes takasagoensis was investigated. 16S rRNA gene sequencing and terminal-restriction fragment length polymorphism (T-RFLP) analyses revealed that the bacterial community structure changed markedly depending on feed components at the phylum level. Spirochaetes was predominant in the clone libraries from wood- and wood powder-fed termites, whereas Bacteroidetes was the largest group in the libraries from xylan-, cellobiose-, and glucose-fed termites, and Firmicutes was predominant in the library from xylose-fed termites. In addition, clones belonging to the phylum Termite Group I (TG1) were found in the library from xylose-fed termites. Our results indicate that the symbiotic relationship between termite and gut microorganisms is not very strong or stable over a short time, and that termite gut microbial community structures vary depending on components of the feeds.     

The solid-state catalytic isotope exchange of hydrogen in dalargin

A [³H]Dalargin preparation with a molar radioactivity of 52 Ci/mmol was obtained by the high temperature solid-state catalytic isotope exchange (HSCIE) of tritium for hydrogen at 150°C. This tritium-labeled peptide was shown to completely retain its biological activity in the test of binding to opioid receptors from rat brain. The dissociation constant of the Dalargin-opioid receptor complex was found to be 4.3 nM. The dependences of the chemical yield and the molar radioactivity on the reaction time and temperature of HSCIE were determined. The activation energy of the HSCIE reaction for the peptide was calculated to be 32 kcal/mol. The amino acid analysis showed that tritium is distributed between all the amino acid residues of [³H]Dalargin at the HSCIE reaction, with the temperature growth significantly increasing the total tritium incorporation and, especially, enhancing the radioactivity incorporation into aromatic residues.