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1.
Influence of pH on Terminal Carbon Metabolism in Anoxic Sediments from a Mildly Acidic Lake 总被引:7,自引:5,他引:2
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The carbon and electron flow pathways and the bacterial populations responsible for transformation of H2-CO2, formate, methanol, methylamine, acetate, glycine, ethanol, and lactate were examined in sediments collected from Knaack Lake, Wis. The sediments were 60% organic matter (pH 6.2) and did not display detectable sulfate-reducing activity, but they contained the following average concentration (in micromoles per liter of sediment) of metabolites and end products: sulfide, 10; methane, 1,540; CO2, 3,950; formate, 25; acetate, 157; ethanol, 174; and lactate, 138. Methane was produced predominately from acetate, and only 4% of the total CH4 was derived from CO2. Methanogenesis was limited by low environmental temperature and sulfide levels and more importantly by low pH. Increasing in vitro pH to neutral values enhanced total methane production rates and the percentage of CO2 transformed to methane but did not alter the amount of 14CO2 produced from [2-14C]acetate (~24%). Analysis of both carbon transformation parameters with 14C-labeled tracers and bacterial trophic group enumerations indicated that methanogenesis from acetate and both heterolactic- and acetic acid-producing fermentations were important to the anaerobic digestion process. 相似文献
2.
Methane production in littoral sediment of Lake Constance 总被引:7,自引:0,他引:7
Maximum rates of CH4 production in the littoral sediment were observed in 2–5 cm depth. The CH4 production rates increased during the year from about 5 mmol m−2d−1 in December to a maximum of about 95 mmol m−2d−1 in September. CH4 production rates showed a temperature optimum at 30°C and an apparent activation energy of 76 kJ mol−1. A large part of the seasonality of CH4 production could be ascribed to the change of the sediment temperature. Most of the produced CH4 was lost by ebullition. Gas bubbles contained about 60–70% CH4 with an average δ13C of −56.2% and δD of −354%, and 2% CO2 with an average δ13C of −14.1% indicating that CH4 was produced from methyl carbon, i.e. mainly using acetate as methanogenic substrate. This result was confirmed by inhibition of methanogenesis with chloroform which resulted in an accumulation rate of acetate equivalent to 81% of the rate of CH4 production. Most probable numbers of methanogenic bacteria were in the order of 104 bacteria g−1d.w. sediment for acetate-, methanol- or formate-utilizing, and of 105 for H2-utilizing methanogens. The turnover times of acetate were in the order of 2.3–4.8 h which, with in situ acetate concentrations of about 25–50 μM, resulted in rates of acetate turnover which were comparable to the rates of CH4 production. The respiratory index (RI) showed that [2−14C]acetate was mainly used by methanogenesis rather than by respiratory processes, although the zone of CH4 production in the sediment overlapped with the zone of sulfate reduction. 相似文献
3.
Effect of rice plants on methane production and rhizospheric metabolism in paddy soil 总被引:10,自引:2,他引:10
In order to elucidate the effects of rice plants on CH4 production, we conducted experiments with soil slurries and planted rice microcosms. Methane production in anoxic paddy soil slurries was stimulated by the addition of rice straw, of unsterile or autoclaved rice roots, and of the culture fluid in which rice plants had axenically been cultivated. The addition of these compounds also increased the concentrations of acetate and H2, precursors of CH4 production, in the soil. Planted compared to unplanted paddy soil microcosms exhibited lower porewater CH4 concentrations but higher CH4 emission rates. They also exhibited higher sulfate concentrations but similar nitrate concentrations. Concentrations of acetate, lactate and H2 were not much different between planted and unplanted microcosms. Pulse labeling of rice plants with14CO2 resulted during the next 5 days in transient accumulation of radioactive lactate, propionate and acetate, and after the second day of incubation in the emission of14CH4. Most of the radioactivity (40–70%) was incorporated into the above-ground biomass of rice plants. However, during a total incubation of 16 days about 3–6% of the applied radioactivity was emitted as14CH4, demonstrating that plant-derived carbon was metabolized and significantly contributed to CH4 production. The sequence of the appearance of radioactive products and their specific radioactivities indicate that CH4 was produced from root exudates by a microbial community consisting of fermenting and methanogenic bacteria. 相似文献
4.
Effect of Fall Turnover on Terminal Carbon Metabolism in Lake Mendota Sediments 总被引:3,自引:2,他引:1
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The carbon and electron flow pathways and the bacterial populations responsible for the transformation of H2-CO2, formate, methanol, methylamine, acetate, ethanol, and lactate were examined in eutrophic sediments collected during summer stratification and fall turnover. The rate of methane formation averaged 1,130 μmol of CH4 per liter of sediment per day during late-summer stratification versus 433 μmol of CH4 per liter of sediment per day during the early portion of fall turnover, whereas the rate of sulfate reduction was 280 μmol of sulfate per liter of sediment per day versus 1,840 μmol of sulfate per liter of sediment per day during the same time periods, respectively. The sulfate-reducing population remained constant while the methanogenic population decreased by one to two orders of magnitude during turnover. The acetate concentration increased from 32 to 81 μmol per liter of sediment while the acetate transformation rate constant decreased from 3.22 to 0.70 per h, respectively, during stratification versus turnover. Acetate accounted for nearly 100% of total sedimentary methanogenesis during turnover versus 70% during stratification. The fraction of 14CO2 produced from all 14C-labeled substrates examined was 10 to 40% higher during fall turnover than during stratification. The addition of sulfate, thiosulfate, or sulfur to stratified sediments mimicked fall turnover in that more CO2 and CH4 were produced. The addition of Desulfovibrio vulgaris to sulfate-amended sediments greatly enhanced the amount of CO2 produced from either [14C]methanol or [2-14C]acetate, suggesting that H2 consumption by sulfate reducers can alter methanol or acetate transformation by sedimentary methanogens. These data imply that turnover dynamically altered carbon transformation in eutrophic sediments such that sulfate reduction dominated over methanogenesis principally as a consequence of altering hydrogen metabolism. 相似文献
5.
Methane production in meromictic Ace Lake,Antarctica 总被引:3,自引:0,他引:3
P. D. Franzmann N. J. Roberts C. A. Mancuso H. R. Burton T. A. McMeekin 《Hydrobiologia》1991,210(3):191-201
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. 相似文献
6.
To determine the rate and mechanism of CH4 production in Lake Biwa sediment, slurry was prepared and incubated. Surface sediment (sed) slurry (1.5–6cm) showed a CH4 release rate (4.9–9.5nmolg-dry-sed–1 day–1) higher than that observed in the 5- to 10-cm sediment slurry (0.2–2nmolg-dry-sed–1 day–1). Methane release from the surface (1.5–6cm) sediment slurry was biotic and was inhibited by addition of 2-bromoethanesulfonate (BES, an inhibitor of CH4 production), whereas that from 5- to 10-cm sediment slurry was abiotic. The addition of BES, HNO3, and O2 showed no effect on the CH4 release rate from the 5- to 10-cm sediment slurry. In addition, tracers (NaH13CO3, 13CH3COONa) were not incorporated into the released CH4. However, 13C of CH4 released from the 5- to 10-cm sediment slurry (–74.0 ± 0.6) indicated that this CH4 was produced by bacterial metabolism in the past, stored by adsorption on the surface of clay minerals in the sediment, and then released abiotically by desorption from the sediment slurry as a result of a decrease in hydraulic pressure and CH4 concentration in the pore water. This CH4 stored by adsorption could be extracted by autoclaving. In the sediment below 5cm, bacterial activity for CH4 production ceased, possibly because of the limitated availability of H2. To clarify the mechanism of CH4 production in the sediment, biotic CH4 production and the abiotic CH4 release found here should be estimated separately. 相似文献
7.
Atmospheric Methane Consumption by Forest Soils and Extracted Bacteria at Different pH Values 总被引:7,自引:3,他引:4
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The effect of pH on atmospheric methane (CH4) consumption was studied with slurries of forest soils and with bacteria extracted from the same soils. Soil samples were collected from a mixed hardwood stand in New Hampshire, from jackpine and aspen stands at the BOREAS (Boreal Ecosystem Atmosphere Study) site near Thompson, northern Manitoba, from sites in southern Québec, including a beech stand and a meadow, and from a site in Ontario (cultivated humisol). Consumption of atmospheric CH4 (concentration, approximately 1.8 ppm) occurred at depths of >5 cm in both acidic (pH 4.5 to 5.2) and alkaline (pH 7.2 to 7.8) soils. In slurries of acidic soils, maximum activity occurred at different pH values (pH 4.0 to 6.5). Bacteria extracted from these soils by high-speed blending and density gradient centrifugation showed pH responses different from the pH responses of the slurries. In all cases, these bacteria had a methanotrophy pH optimum of 5.8 and exhibited no activity at pH 6.8 to 7.0, the pH optimum range for known methanotrophs. This difference in pH responses could be useful in modifying media currently used for isolation of these organisms. Methanotrophic activity was induced in previously non-CH4-consuming soils by preincubation with 5% (vol/vol) CH4 (50,000 μl of CH4 per liter) or by liquid enrichment with 20% CH4. The bacteria showed pH responses typical of known methanotrophs and not typical of preexisting consumers of ambient CH4. Furthermore, methanotrophs induced by high CH4 levels were more readily extracted from soil than preexisting ambient CH4 consumers were. In the alkaline soils, preexisting activity either was destroyed or resisted extraction by the procedure used. The results support the hypothesis that consumers of ambient CH4 in soils are physiologically distinct from the known methanotrophs. 相似文献
8.
S. V. Bukin O. N. Pavlova G. V. Kalmychkov V. G. Ivanov T. V. Pogodaeva Yu. P. Galach’yants Yu. S. Bukin A. V. Khabuev T. I. Zemskaya 《Microbiology》2018,87(4):549-558
Methane production by microbial communities from Lake Baikal bottom sediments with different chemical composition of pore water was studied. Methane production was more active in the media supplemented with H2: CO2 and H2 + CH3COONa, rather than on media with acetate as the sole source of carbon and energy. Addition of methanol stimulated methane production only in the case of microbial communities from upper silts. Ability of the communities to produce methane correlated reliably with the concentrations of the NO3–, SO42?, Cl–, and CH3COO– ions in the pore water of the relevant sediments. Cultivation of communities from the mud volcano sediments resulted in development of methanogenic archaea of the family Methanocellaсеае in the media supplemented with H2: CO2 and H2 + CH3COONa, while methanogenic archaea in the communities cultivated without additional substrates belonged to the genera Methanoregula, Methanobacterium, and Methanosaeta. 相似文献
9.
Methanogenesis and the anaerobic metabolism of acetate were examined in the sediment and water column of Knaack Lake, a small biogenic meromictic lake located in central Wisconsin. The lake was sharply stratified during the summer and was anaerobic below a depth of 3 m. Large concentrations (4,000 μmol/liter) of dissolved methane were detected in the bottom waters. A methane concentration maximum occurred at 4 m above the sediment. The production of 14CH4 from 14C-labeled HCOOH, HCO3−, and CH3OH and [2-14C]acetate demonstrated microbial methanogenesis in the water column of the lake. The maximum rate of methanogenesis calculated from reduction of H14CO3− by endogenous electron donors in the surface sediment (depth, 22 m) was 7.6 nmol/h per 10 ml and in the water column (depth, 21 m) was 0.6 nmol/h per 10 ml. The methyl group of acetate was simultaneously metabolized to CH4 and CO2 in the anaerobic portions of the lake. Acetate oxidation was greatest in surface waters and decreased with water depth. Acetate was metabolized primarily to methane in the sediments and water immediately above the sediment. Sulfide inhibition studies and temperature activity profiles demonstrated that acetate metabolism was performed by several microbial populations. Sulfide additions (less than 5 μg/ml) to water from 21.5 m stimulated methanogenesis from acetate, but inhibited CO2 production. Sulfate addition (1 mM) had no significant effect on acetate metabolism in water from 21.5 m, whereas nitrate additions (10 to 14,000 μg/liter) completely inhibited methanogenesis and stimulated CO2 formation. 相似文献
10.
Evaluation of Methyl Fluoride and Dimethyl Ether as Inhibitors of Aerobic Methane Oxidation 总被引:7,自引:11,他引:7
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Methyl fluoride (MF) and dimethyl ether (DME) were effective inhibitors of aerobic methanotrophy in a variety of soils. MF and DME blocked consumption of CH4 as well as the oxidation of 14CH4 to 14CO2, but neither MF nor DME affected the oxidation of [14C]methanol or [14C]formate to 14CO2. Cooxidation of ethane and propane by methane-oxidizing soils was also inhibited by MF. Nitrification (ammonia oxidation) in soils was inhibited by both MF and DME. Production of N2O via nitrification was inhibited by MF; however, MF did not affect N2O production associated with denitrification. Methanogenesis was partially inhibited by MF but not by DME. Methane oxidation was ~100-fold more sensitive to MF than was methanogenesis, indicating that an optimum concentration could be employed to selectively block methanotrophy. MF inhibited methane oxidation by cell suspensions of Methylococcus capsulatus; however, DME was a much less effective inhibitor. 相似文献
11.
Effects of Methane Metabolism on Nitrification and Nitrous Oxide Production in Polluted Freshwater Sediment 总被引:4,自引:2,他引:2
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We report the effect of CH4 and of CH4 oxidation on nitrification in freshwater sediment from Hamilton Harbour, Ontario, Canada, a highly polluted ecosystem. Aerobic slurry experiments showed a high potential for aerobic N2O production in some sites. It was suppressed by C2H2, correlated to NO3- production, and stimulated by NH4+ concentration, supporting the hypothesis of a nitrification-dependent source for this N2O production. Diluted sediment slurries supplemented with CH4 (1 to 24 μM) showed earlier and enhanced nitrification and N2O production compared with unsupplemented slurries (≤1 μM CH4). This suggests that nitrification by methanotrophs may be significant in freshwater sediment under certain conditions. Suppression of nitrification was observed at CH4 concentrations of 84 μM and greater, possibly through competition for O2 between methanotrophs and NH4+ -oxidizing bacteria and/or competition for mineral N between these two groups of organisms. In Hamilton Harbour sediment, the very high CH4 concentrations (1.02 to 6.83 mM) which exist would probably suppress nitrification and favor NH4+ accumulation in the pore water. Indeed, NH4+ concentrations in Hamilton Harbour sediment are higher than those found in other lakes. We conclude that the impact of CH4 metabolism on N cycling processes in freshwater ecosystems should be given more attention. 相似文献
12.
The abundance and distribution of dissolved CH4 were determined from 1987–1990 in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement
is controlled by diffusion. CH4 concentrations were < 1 υM in the upper oxic waters, but increased below the oxycline to 936 μM at 18 m. Sediment CH4 was 1100 μmol (1 sed)−1 in the 0–5 cm zone. Upward flux from the sediment was the source of the CH4, NH4
+, and DOC in the water column; CH4 was 27% of the DOC+CH4 carbon at 18 m. Incubations with surficial sediments indicated that H14CO3
− reduction was 0.4 μmol (1 sed)−1 day−1 or 4× the rate of acetate fermentation to CH4. There was no measurable CH4 production in the water column. However, depth profiles of CH4, NH4, and DIC normalized to bottom water concentrations demonstrated that a significant CH4 sink was evident in the anoxic, sulfate-containing zone of the water column (10–18 m). The δ13CH4 in this zone decreased from −72 % at 18 m to −76% at 12 m, indicating that the consumption mechanism did not result in an
isotopic enrichment of 13CH4. In contrast, δ13CH4 increased to −55 % at 9 m due to aerobic oxidation, though this was a minor aspect of the CH4 cycle. The water column CH4 profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic
CH4 consumption was 0.012 yr−1. On a total carbon basis, CH4 consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments
and serves to exemplify the importance of CH4 to carbon cycling in Lake Fryxell. 相似文献
13.
Comparison of unitrophic and mixotrophic substrate metabolism by acetate-adapted strain of Methanosarcina barkeri 总被引:22,自引:12,他引:10
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We examined the unitrophic metabolism of acetate and methanol individually and the mixotrophic utilization of these compounds by using detailed 14C-labeled tracer studies in a strain of Methanosarcina barkeri adapted to grow on acetate as the sole carbon and energy source. The substrate consumption rate and methane production rate were significantly lower on acetate alone than during the unitrophic or mixotrophic metabolism of methanol. Cell yields (in grams per mole of substrate) were identical during exponential growth on acetate and exponential growth on methanol. During unitrophic metabolism of acetate, the methyl moiety accounted for the majority of the CH4 produced, but 14% of the CO2 generated originated from the methyl moiety. This correlated with the concurrent reduction of equivalent amounts of the C-1 of acetate to CH4. 14CH4 was also produced from added 14CO2, although to a lesser extent than from reduction of the C-1 of acetate. During mixotrophic metabolism, methanol and acetate were catabolized simultaneously. The rates of 14CH4 and 14CO2 generation from [2-14C]acetate were logarithmic and higher in mixotrophic than in unitrophic cultures at substrate concentrations of 50 mM. A comparison of the oxidoreductase activities in cell extracts of the acetate-adapted strain grown on acetate and of strain MS grown on methanol or on H2 plus CO2 indicated that the pyruvate, α-ketoglutarate, and isocitrate dehydrogenase activities remained constant, whereas the CO dehydrogenase activity was significantly higher (5,000 nmol/min per mg of protein) in the acetate-adapted strain. These results suggested that a significant intramolecular redox pathway is possible for the generation of CH4 from acetate, that energy metabolism from acetate by M. barkeri is not catabolite repressed by methanol, and that the acetate-adapted strain is a metabolic mutant with derepressed CO dehydrogenase activity. 相似文献
14.
Rates of methane production in Minnesota peats were studied. Surface (10- to 25-cm) peats produced an average of 228 nmol of CH4 per g (dry weight) per h at 25°C and ambient pH. Methanogenesis rates generally decreased with depth in ombrotrophic peats, but on occasion were observed to rise within deeper layers of certain fen peats. Methane production was temperature dependent, increasing with increasing temperature (4 to 30°C), except in peats from deeper layers. Maximal methanogenesis from these deeper regions occurred at 12°C. Methane production rates were also pH dependent. Two peats with pHs of 3.8 and 4.3 had an optimum rate of methane production at pH 6.0. The addition to peat of glucose and H2-CO2 stimulated methanogenesis, whereas the addition of acetate inhibited methanogenesis. Cysteine-sulfide, nitrogen-phosphorus-trace metals, and vitamins-yeast extract affected methane production very little. Various gases were found to be trapped or dissolved (or both) within peatland waters. Dissolved methane increased linearly to a depth of 210 cm. The accumulation of metabolic end products produced within peat bogs appears to be an important mechanism limiting carbon turnover in peatland environments. 相似文献
15.
Intermediary Metabolism of Organic Matter in the Sediments of a Eutrophic Lake 总被引:38,自引:34,他引:4
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The rates, products, and controls of the metabolism of fermentation intermediates in the sediments of a eutrophic lake were examined. 14C-fatty acids were directly injected into sediment subcores for turnover rate measurements. The highest rates of acetate turnover were in surface sediments (0- to 2-cm depth). Methane was the dominant product of acetate metabolism at all depths. Simultaneous measurements of acetate, propionate, and lactate turnover in surface sediments gave turnover rates of 159, 20, and 3 μM/h, respectively. [2-14C]propionate and [U-14C]lactate were metabolized to [14C]acetate, 14CO2, and 14CH4. [14C]formate was completely converted to 14CO2 in less than 1 min. Inhibition of methanogenesis with chloroform resulted in an immediate accumulation of volatile fatty acids and hydrogen. Hydrogen inhibited the metabolism of C3-C5 volatile fatty acids. The rates of fatty acid production were estimated from the rates of fatty acid accumulation in the presence of chloroform or hydrogen. The mean molar rates of production were acetate, 82%; propionate, 13%; butyrates, 2%; and valerates, 3%. A working model for carbon and electron flow is presented which illustrates that fermentation and methanogenesis are the predominate steps in carbon flow and that there is a close interaction between fermentative bacteria, acetogenic hydrogen-producing bacteria, and methanogens. 相似文献
16.
Methane emission and rhizospheric CH4 oxidation were studied in stands of Equisetum fluviatile, a common cryptogam in boreal lakes. The experiment was performed in mesocosms with organic sediment or sand bottoms under natural variation of temperature and light using the light-oxic – dark-anoxic chamber (LO/DA) technique. Net CH4 emission from the organic sediment during the growing season varied between 3.4 and 19.0 mg m–2 h–1, but from sand the net CH4 emission was only 3–10% of that measured from the organic sediment. In the organic sediment net CH4 emission was very significantly correlated with sediment temperature (r2 = 0.92). In the sand mesocosms the variation of net CH4 emission was better correlated with the shoot biomass than with sediment temperature variation during the growing season, indicating that methanogens were severely limited by substrate availability and were probably dependent on substrates produced by E. fluviatile. The proportion of the methane oxidized of the potential CH4 emission in summer did not differ significantly between the bottom types. The net CH4 emission during the growing season as a proportion of the seasonal maximum of the shoot biomass was significantly higher in the organic sediment mesocosms (6.5%) than in sand (1.7%). The high CH4 emissions observed from dense well-established E. fluviatile stands in the field appear to be more related to temperature-regulated turnover of detritus in the anaerobic sediment and less to CH4 oxidation and seasonal variation in plant growth dynamics 相似文献
17.
Irrigated rice fields are an important source of atmospheric methane. In order to improve our understanding of the controlling processes, we measured in situ CH4 emission and CH4 oxidation in an Italian rice field in 1998 and 1999, and studied CH4 production in soil and root samples. The CH4 emission rates were correlated with diurnal temperature variations and showed pronounced seasonal and interannual variations. The contribution of CH4 oxidation to total CH4 flux, determined by specific inhibition with difluoromethane, decreased from 40% at the beginning to zero at the end of the season. The stable carbon isotopic composition of the emitted CH4 also decreased. The CH4‐oxidizing bacteria probably became limited by nitrogen as indicated by the seasonal decrease of NH4+. Thus, CH4 oxidation had little effect on CH4 emission. Methane production on rice roots was relatively constant over the season. Methane production in soil slowly increased after flooding and was highest in the middle of the season. Pore water concentrations of CH4 showed a similar seasonal pattern. In 1999, CH4 production increased later in the season and reached lower rates than in 1998. An additional drainage in 1999 resulted in higher ferric iron concentrations, higher soil redox potentials and lower acetate concentrations. As a result, acetate‐utilizing methanogens were probably out‐competed by iron‐reducers so that a larger percentage of [2–14C]acetate was converted to 14CO2 instead of 14CH4. The residual CH4 production was relatively low and was mainly due to H2/CO2‐dependent methanogenesis. Experiments with radioactive bicarbonate and with methyl fluoride as specific inhibitor showed that the theoretical ratio of 7:3 of methanogenesis from acetate vs. H2/CO2 was only reached later in the season when total CH4 production was at the maximum. In conclusion, our results give a mechanistic explanation for the intraseasonal and interannual differences in CH4 emission. 相似文献
18.
Mercury Methylation and Demethylation in Anoxic Lake Sediments and by Strictly Anaerobic Bacteria 总被引:10,自引:4,他引:6
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After spiking anoxic sediment slurries of three acidic oligotrophic lakes with either HgCl2 at 1.0 μg/ml or CH3HgI at 0.1 μg/ml, both mercury methylation and demethylation rates were measured. High mercury methylation potentials were accompanied by high demethylation potentials in the same sediment. These high potentials correlated positively with the concentrations of organic matter and dissolved sulfate in the sediment and with mercury levels in fish. Adjustment of the acidic sediment pH to neutrality failed to influence either the methylation or the demethylation rate of mercury. The opposing methylation and demethylation processes converged to establish similar Hg2+-CH3Hg+ equilibria in all three sediments. Because of their metabolic dominance in anoxic sediments, mercury methylation and demethylation in pure cultures of sulfidogenic, methanogenic, and acetogenic bacteria were also measured. Sulfidogens both methylated and demethylated mercury, but the methanogen tested only catalyzed demethylation and the acetogen neither methylated nor demethylated mercury. 相似文献
19.
Hydrogenotrophic Methanogenesis by Moderately Acid-Tolerant Methanogens of a Methane-Emitting Acidic Peat 总被引:7,自引:6,他引:1
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Marcus A. Horn Carola Matthies Kirsten Küsel Andreas Schramm Harold L. Drake 《Applied microbiology》2003,69(1):74-83
The emission of methane (1.3 mmol of CH4 m−2 day−1), precursors of methanogenesis, and the methanogenic microorganisms of acidic bog peat (pH 4.4) from a moderately reduced forest site were investigated by in situ measurements, microcosm incubations, and cultivation methods, respectively. Bog peat produced CH4 (0.4 to 1.7 μmol g [dry wt] of soil−1 day−1) under anoxic conditions. At in situ pH, supplemental H2-CO2, ethanol, and 1-propanol all increased CH4 production rates while formate, acetate, propionate, and butyrate inhibited the production of CH4; methanol had no effect. H2-dependent acetogenesis occurred in H2-CO2-supplemented bog peat only after extended incubation periods. Nonsupplemented bog peat initially produced small amounts of H2 that were subsequently consumed. The accumulation of H2 was stimulated by ethanol and 1-propanol or by inhibiting methanogenesis with bromoethanesulfonate, and the consumption of ethanol was inhibited by large amounts of H2; these results collectively indicated that ethanol- or 1-propanol-utilizing bacteria were trophically associated with H2-utilizing methanogens. A total of 109 anaerobes and 107 hydrogenotrophic methanogens per g (dry weight) of bog peat were enumerated by cultivation techniques. A stable methanogenic enrichment was obtained with an acidic, H2-CO2-supplemented, fatty acid-enriched defined medium. CH4 production rates by the enrichment were similar at pH 4.5 and 6.5, and acetate inhibited methanogenesis at pH 4.5 but not at pH 6.5. A total of 27 different archaeal 16S rRNA gene sequences indicative of Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae were retrieved from the highest CH4-positive serial dilutions of bog peat and methanogenic enrichments. A total of 10 bacterial 16S rRNA gene sequences were also retrieved from the same dilutions and enrichments and were indicative of bacteria that might be responsible for the production of H2 that could be used by hydrogenotrophic methanogens. These results indicated that in this acidic bog peat, (i) H2 is an important substrate for acid-tolerant methanogens, (ii) interspecies hydrogen transfer is involved in the degradation of organic carbon, (iii) the accumulation of protonated volatile fatty acids inhibits methanogenesis, and (iv) methanogenesis might be due to the activities of methanogens that are phylogenetic members of the Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae. 相似文献
20.
A possibility of dissimilatory MnO2 reduction at extremely high salt and pH was studied in sediments from hypersaline alkaline lakes in Kulunda Steppe (Altai,
Russia). Experiments with anaerobic sediment slurries demonstrated a relatively rapid reduction of colloidal MnO2 in the presence of acetate and formate as electron donor at in situ conditions (i.e., pH 10 and a salt content from 0.6 to
4 M total Na+). All reduced Mn at these conditions remained in the solid phase. A single, stable enrichment culture was obtained from the
slurries consistently reducing MnO2 at pH 10 and 0.6 M total Na+ with formate. A pure culture of a haloalkaliphilic Mn-reducing bacterium obtained from the positive enrichment was phylogenetically
closely related to the anaerobic haloalkaliphilic Bacillus arseniciselenatis isolated from Mono Lake (CA, USA). Bacillus sp. strain AMnr1 was obligately anaerobic, able to grow either by glucose fermentation, or respiring few nonfermentable substrates
by using MnO2 as the electron acceptor. Optimal growth by dissimilatory MnO2 reduction was achieved with glycerol as electron donor at pH 9.5–10 and salt content between 0.4 and 0.8 M total Na+. 相似文献