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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.
Partitioning Effects during Terminal Carbon and Electron Flow in Sediments of a Low-Salinity Meltwater Pond near Bratina Island, McMurdo Ice Shelf, Antarctica 总被引:1,自引:1,他引:0
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Douglas O. Mountfort Heinrich F. Kaspar Malcolm Downes Rodney A. Asher 《Applied microbiology》1999,65(12):5493-5499
A study of anaerobic sediments below cyanobacterial mats of a low-salinity meltwater pond called Orange Pond on the McMurdo Ice Shelf at temperatures simulating those in the summer season (<5°C) revealed that both sulfate reduction and methane production were important terminal anaerobic processes. Addition of [2-14C]acetate to sediment samples resulted in the passage of label mainly to CO2. Acetate addition (0 to 27 mM) had little effect on methanogenesis (a 1.1-fold increase), and while the rate of acetate dissimilation was greater than the rate of methane production (6.4 nmol cm−3 h−1 compared to 2.5 to 6 nmol cm−3 h−1), the portion of methane production attributed to acetate cleavage was <2%. Substantial increases in the methane production rate were observed with H2 (2.4-fold), and H2 uptake was totally accounted for by methane production under physiological conditions. Formate also stimulated methane production (twofold), presumably through H2 release mediated through hydrogen lyase. Addition of sulfate up to 50-fold the natural levels in the sediment (interstitial concentration, ~0.3 mM) did not substantially inhibit methanogenesis, but the process was inhibited by 50-fold chloride (36 mM). No net rate of methane oxidation was observed when sediments were incubated anaerobically, and denitrification rates were substantially lower than rates for sulfate reduction and methanogenesis. The results indicate that carbon flow from acetate is coupled mainly to sulfate reduction and that methane is largely generated from H2 and CO2 where chloride, but not sulfate, has a modulating role. Rates of methanogenesis at in situ temperatures were four- to fivefold less than maximal rates found at 20°C. 相似文献
3.
Interrelations between sulfate-reducing and methane-producing bacteria in bottom deposits of a fresh-water lake. III. Experiments with 14C-labeled substrates 总被引:31,自引:0,他引:31
An ecological substrate relationship between sulfate-reducing and methane-producing bacteria in mud of Lake Vechten has been studied in experiments using 14C-labeled acetate and lactate as substrates. Fluoroacetate strongly inhibited the formation of 14CO2 from [U-14C]-acetate and β-fluorolactate gave an inhibition of similar magnitude of the breakdown of [U-14C]-l-lactate to 14CO2 thus confirming earlier results on the specific action of these inhibitors. The turnover-rate constant of l-lactate was 2.37 hr-1 and the average l-lactate pool size was 12.2 μg per gram of wet mud, giving a turnover rate of 28.9 μg of lactate/gram of mud per hr. The turnover-rate constant of acetate was 0.35 hr-1 and the average pool size was 5.7 μg per gram of wet mud, giving a rate of disappearance of 1.99 μg of acetate/gram of mud per hr. Estimations of the acetate turnover rate based upon the formation of 14CO2 from [U-14C]-acetate or [1-14C]-acetate yielded figures of the same magnitude (range 0.45 to 1.74). These and other results suggest that only a portion of the lactate dissimilated is turned over through the acetate pool. The ratio of 14CO2/14CH4 produced from [U-14C]-acetate by mud was 1.32; indicating that 0.862 moles of CH4 and 1.138 moles of CO2 are formed per mole of acetate. From the rate of disappearance of acetate (0.027 μmoles/gram wet mud per hr) and the rate of methane production (0.034 μmoles/gram wet mud per hr), it may be concluded that acetate is an important precursor of methanogenesis in mud (approximately 70%). A substrate relationship between the two groups of bacteria is likely since 14CH4 was formed from [U-14C]-l-lactate. 相似文献
4.
Anaerobic Degradation of Lactate by Syntrophic Associations of Methanosarcina barkeri and Desulfovibrio Species and Effect of H2 on Acetate Degradation 总被引:18,自引:13,他引:5
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When grown in the absence of added sulfate, cocultures of Desulfovibrio desulfuricans or Desulfovibrio vulgaris with Methanobrevibacter smithii (Methanobacterium ruminantium), which uses H2 and CO2 for methanogenesis, degraded lactate, with the production of acetate and CH4. When D. desulfuricans or D. vulgaris was grown in the absence of added sulfate in coculture with Methanosarcina barkeri (type strain), which uses both H2-CO2 and acetate for methanogenesis, lactate was stoichiometrically degraded to CH4 and presumably to CO2. During the first 12 days of incubation of the D. desulfuricans-M. barkeri coculture, lactate was completely degraded, with almost stoichiometric production of acetate and CH4. Later, acetate was degraded to CH4 and presumably to CO2. In experiments in which 20 mM acetate and 0 to 20 mM lactate were added to D. desulfuricans-M. barkeri cocultures, no detectable degradation of acetate occurred until the lactate was catabolized. The ultimate rate of acetate utilization for methanogenesis was greater for those cocultures receiving the highest levels of lactate. A small amount of H2 was detected in cocultures which contained D. desulfuricans and M. barkeri until after all lactate was degraded. The addition of H2, but not of lactate, to the growth medium inhibited acetate degradation by pure cultures of M. barkeri. Pure cultures of M. barkeri produced CH4 from acetate at a rate equivalent to that observed for cocultures containing M. barkeri. Inocula of M. barkeri grown with H2-CO2 as the methanogenic substrate produced CH4 from acetate at a rate equivalent to that observed for acetate-grown inocula when grown in a rumen fluid-vitamin-based medium but not when grown in a yeast extract-based medium. The results suggest that H2 produced by the Desulfovibrio species during growth with lactate inhibited acetate degradation by M. barkeri. 相似文献
5.
Control of Interspecies Electron Flow during Anaerobic Digestion: Significance of Formate Transfer versus Hydrogen Transfer during Syntrophic Methanogenesis in Flocs 总被引:18,自引:11,他引:7
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Microbial formate production and consumption during syntrophic conversion of ethanol or lactate to methane was examined in purified flocs and digestor contents obtained from a whey-processing digestor. Formate production by digestor contents or purified digestor flocs was dependent on CO2 and either ethanol or lactate but not H2 gas as an electron donor. During syntrophic methanogenesis, flocs were the primary site for formate production via ethanol-dependent CO2 reduction, with a formate production rate and methanogenic turnover constant of 660 μM/h and 0.044/min, respectively. Floc preparations accumulated fourfold-higher levels of formate (40 μM) than digestor contents, and the free flora was the primary site for formate cleavage to CO2 and H2 (90 μM formate per h). Inhibition of methanogenesis by CHCl3 resulted in formate accumulation and suppression of syntrophic ethanol oxidation. H2 gas was an insignificant intermediary metabolite of syntrophic ethanol conversion by flocs, and its exogenous addition neither stimulated methanogenesis nor inhibited the initial rate of ethanol oxidation. These results demonstrated that >90% of the syntrophic ethanol conversion to methane by mixed cultures containing primarily Desulfovibrio vulgaris and Methanobacterium formicicum was mediated via interspecies formate transfer and that <10% was mediated via interspecies H2 transfer. The results are discussed in relation to biochemical thermodynamics. A model is presented which describes the dynamics of a bicarbonate-formate electron shuttle mechanism for control of carbon and electron flow during syntrophic methanogenesis and provides a novel mechanism for energy conservation by syntrophic acetogens. 相似文献
6.
Growth and Methanogenesis by Methanosarcina Strain 227 on Acetate and Methanol 总被引:18,自引:11,他引:7
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Methanosarcina strain 227 exhibited exponential growth on sodium acetate in the absence of added H2. Under these conditions, rates of methanogenesis were limited by concentrations of acetate below 0.05 M. One mole of methane was formed per mole of acetate consumed. Additional evidence from radioactive labeling studies indicated that sufficient energy for growth was obtained by the decarboxylation of acetate. Diauxic growth and sequential methanogenesis from methanol followed by acetate occurred in the presence of mixtures of methanol and acetate. Detailed studies showed that methanol-grown cells did not metabolize acetate in the presence of methanol, although acetate-grown cells did metabolize methanol and acetate simultaneously before shifting to methanol. Acetate catabolism appeared to be regulated in response to the presence of better metabolizable substrates such as methanol or H2-CO2 by a mechanism resembling catabolite repression. Inhibition of methanogenesis from acetate by 2-bromoethanesulfonate, an analog of coenzyme M, was reversed by addition of coenzyme M. Labeling studies also showed that methanol may lie on the acetate pathway. These results suggested that methanogenesis from acetate, methanol, and H2-CO2 may have some steps in common, as originally proposed by Barker. Studies with various inhibitors, together with molar growth yield data, suggest a role for electron transport mechanisms in energy metabolism during methanogenesis from methanol, acetate, and H2-CO2. 相似文献
7.
A tritium exchange assay and a sensitive gas chromatographic technique were used to demonstrate that hydrogenase was active and that hydrogen was produced by Methanosarcina barkeri strain MS grown on acetate. Both methane and hydrogen production rates were dependent on the concentration of acetate in the medium. H2 was produced at 0.5–2% of the rate of CH4 formation. Chloroform and potassium cyanide, inhibitors of methanogenesis from acetate, inhibited H2 production but not hydrogenase activity. The addition of hydrogen gas to cell suspensions did not inhibit CH4 or carbon dioxide production from the methyl group of acetate. H2 production appears to be linked to several intracellular redox processes which follow the cleavage of acetate. 相似文献
8.
Growth of Desulfovibrio in Lactate or Ethanol Media Low in Sulfate in Association with H2-Utilizing Methanogenic Bacteria 总被引:37,自引:29,他引:8
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In the analysis of an ethanol-CO2 enrichment of bacteria from an anaerobic sewage digestor, a strain tentatively identified as Desulfovibrio vulgaris and an H2-utilizing methanogen resembling Methanobacterium formicicum were isolated, and they were shown to represent a synergistic association of two bacterial species similar to that previously found between S organism and Methanobacterium strain MOH isolated from Methanobacillus omelianskii. In lowsulfate media, the desulfovibrio produced acetate and H2 from ethanol and acetate, H2, and, presumably, CO2 from lactate; but growth was slight and little of the energy source was catabolized unless the organism was combined with an H2-utilizing methanogenic bacterium. The type strains of D. vulgaris and Desulfovibrio desulfuricans carried out the same type of synergistic growth with methanogens. In mixtures of desulfovibrio and strain MOH growing on ethanol, lactate, or pyruvate, diminution of methane produced was stoichiometric with the moles of sulfate added, and the desulfovibrios grew better with sulfate addition. The energetics of the synergistic associations and of the competition between the methanogenic system and sulfate-reducing system as sinks for electrons generated in the oxidation of organic materials such as ethanol, lactate, and acetate are discussed. It is suggested that lack of availability of H2 for growth of methanogens is a major factor in suppression of methanogenesis by sulfate in natural ecosystems. The results with these known mixtures of bacteria suggest that hydrogenase-forming, sulfate-reducing bacteria could be active in some methanogenic ecosystems that are low in sulfate. 相似文献
9.
Sulfate Reduction Relative to Methane Production in High-Rate Anaerobic Digestion: Technical Aspects 总被引:5,自引:2,他引:3
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The effect of different substrates and different levels of sulfate and sulfide on methane production relative to sulfate reduction in high-rate anaerobic digestion was evaluated. Reactors could be acclimated so that sulfate up to a concentration of 5 g of sulfate S per liter did not significantly affect methanogenesis. Higher levels gave inhibition because of salt toxicity. Sulfate reduction was optimal at a relatively low level of sulfate, i.e., 0.5 g of sulfate S per liter, but was also not significantly affected by higher levels. Both acetoclastic and hydrogenotrophic methane-producing bacteria adapted to much higher levels of free H2S than the values reported in the literature (50% inhibition occurred only at free H2S levels of more than 1,000 mg/liter). High levels of free H2S affected the sulfate-reducing bacteria only slightly. Formate and acetate supported the sulfate-reducing bacteria very poorly. In the high-rate reactors studied, intensive H2S formation occurred only when H2 gas or an H2 precursor such as ethanol was supplied. 相似文献
10.
Stable Carbon Isotope Fractionation by Methanosarcina barkeri during Methanogenesis from Acetate, Methanol, or Carbon Dioxide-Hydrogen 总被引:3,自引:1,他引:2
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Methanosarcina barkeri was cultured on methanol, H2-CO2, and acetate, and the 13C/12C ratios of the substrates and the methane produced from them were determined. The discrimination against 13C in methane relative to substrate decreased in the order methanol > CO2 > acetate. The isotopic fractionation for methane derived from acetate was only one-third of that observed with methanol as the substrate. The data presented indicate that the last enzyme of methanogenesis, methylreductase, is not the primary site of isotopic discrimination during methanogenesis from methanol or CO2. These results also support biogeochemical interpretations that gas produced in environments in which acetate is the primary methane precursor will have higher 13C/12C ratios than those from environments where other substrates predominate. 相似文献
11.
Trophic links between fermentation and methanogenesis of soil derived from a methane‐emitting, moderately acidic temperate fen (pH 4.5) were investigated. Initial CO2:CH4 production ratios in anoxic microcosms indicated that methanogenesis was concomitant to other terminal anaerobic processes. Methane production in anoxic microcosms at in situ pH was stimulated by supplemental H2–CO2, formate or methanol; supplemental acetate did not stimulate methanogenesis. Supplemental H2–CO2, formate or methanol also stimulated the formation of acetate, indicating that the fen harbours moderately acid‐tolerant acetogens. Supplemental monosaccharides (glucose, N‐acetylglucosamine and xylose) stimulated the production of CO2, H2, acetate and other fermentation products when methanogenesis was inhibited with 2‐bromoethane sulfonate 20 mM. Glucose stimulated methanogenesis in the absence of BES. Upper soil depths yielded higher anaerobic activities and also higher numbers of cells. Detected archaeal 16S rRNA genes were indicative of H2–CO2‐ and formate‐consuming methanogens (Methanomicrobiaceae), obligate acetoclastic methanogens (Methanosaetaceae) and crenarchaeotes (groups I.1a, I.1c and I.3). Molecular analyses of partial sequences of 16S rRNA genes revealed the presence of Acidobacteria, Nitrospirales, Clamydiales, Clostridiales, Alpha‐, Gamma‐, Deltaproteobacteria and Cyanobacteria. These collective results suggest that this moderately acidic fen harbours phylogenetically diverse, moderately acid tolerant fermenters (both facultative aerobes and obligate anaerobes) that are trophically linked to methanogenesis. 相似文献
12.
In a mesophilic (37°C) triculture at a high ammonium concentration and pH8, methanogenesis from acetate occurred via syntrophic acetate oxidation. Studies with 14C-labelled substrates showed that the amount of labelled methane formed from 1-14C-labelled acetate was equal to that formed from 2-14C-labelled acetate. Labelled methane was also formed from H14CO3
-. These results clearly showed that both the methyl and carboxyl groups of acetate were oxidized to CO2 and that CO2 was reduced to CH4 through hydrogenotrophic methanogenesis. During growth of the triculture, a significant isotopic exchange between the carboxyl group of acetate and bicarbonate occurred. As a result, there was a decrease in the specific activity of 1-14C-acetate, and the production of 14CO2 was slightly higher from 1-14C- than from 2-14C-acetate. For each mole acetate degraded, 0.94 mol methane was formed; 9.2 mmol acetate was metabolized during the 294 days of incubation. 相似文献
13.
Fate of Immediate Methane Precursors in Low-Sulfate, Hot-Spring Algal-Bacterial Mats 总被引:11,自引:7,他引:4
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The fates of acetate and carbon dioxide were examined in several experiments designed to indicate their relative contributions to methane production at various temperatures in two low-sulfate, hot-spring algal-bacterial mats. [2-14C]acetate was predominantly incorporated into cell material, although some 14CH4 and 14CO2 was produced. Acetate incorporation was reduced by dark incubation in short-term experiments and severely depressed by a 2-day preincubation in darkness. Autoradiograms showed that acetate was incorporated by long filaments resembling phototrophic microorganisms of the mat communities. [3H]acetate was not converted to C3H4 in samples from Octopus Spring collected at the optimum temperature for methanogenesis. NaH14CO3 was readily converted to 14CH4 at temperatures at which methanogenesis was active in both mats. Comparisons of the specific activities of methane and carbon dioxide suggested that of the methane produced, 80 ± 6% in Octopus Spring and 71 ± 21% in Wiegert Channel were derived from carbon dioxide. Addition of acetate to 1 mM did not reduce the relative importance of carbon dioxide as a methane precursor in samples from Octopus Spring. Experiments with pure cultures of Methanobacterium thermoautotrophicum suggested that the measured ratio of specific activities might underestimate the true contribution of carbon dioxide in methanogenesis. 相似文献
14.
Hydrogen gas stimulated sulphate reduction in a saltmarsh sediment and the importance of H2 transferred from organotrophic bacteria to the sulphate-reducers is discussed. -fluorolactate inhibited sulphate reduction whether lactate, ethanol or hydrogen was being used as growth substrate. When added to sediment -fluorolactate inhibited sulphate reduction with a consequent increase in methane production.Addition of H2 stimulated methanogenesis in sediment and this stimulation was greater if CO2 was also present. Hydrogen availability was the primary limitation of methanogenesis but the low concentration of dissolved CO2 in seawater may limit methane production even if H2 is available.The removal of inhibition of methanogenesis by the use of fluorolactate to suppress sulphate reduction or by the provision of hydrogen indicates competitive inhibition of methanogens by sulphate reducers utilizing transferred hydrogen.Abbreviations HSRB
hydrogen utilizing sulphate reducing bacteria
- HDO
hydrogen donating organism 相似文献
15.
T. N. Nazina N. M. Shestakova A. A. Grigor’yan E. M. Mikhailova T. P. Tourova A. B. Poltaraus Cingxian Feng Fangtian Ni S. S. Belyaev 《Microbiology》2006,75(1):55-65
The number of microorganisms of major metabolic groups and the rates of sulfate reduction and methanogenesis processes in the formation waters of the high-temperature horizons of Dagang oil field have been determined. Using cultural methods, it was shown that the microbial community contained aerobic bacteria oxidizing crude oil, anaerobic fermentative bacteria, sulfate-reducing bacteria, and methanogens. Using cultural methods, the possibility of methane production from a mixture of hydrogen and carbon dioxide (H2 + CO2) and from acetate was established, and this result was confirmed by radioisotope methods involving NaH14CO3 and 14CH3COONa. Analysis of enrichment cultures 16S rDNA of methanogens demonstrated that these microorganisms belong to Methanothermobacter sp. (M. thermautotrophicus), which consumes hydrogen and carbon dioxide as basic substrates. The genes of acetate-utilizing bacteria were not revealed. Phylotypes of the representatives of Thermococcus spp. were found among archaeal 16S rDNA. 16S rRNA genes of bacterial clones belong to the orders Thermoanaerobacteriales (Thermoanaerobacter, Thermovenabulum, Thermacetogenium, and Coprothermobacter spp.), Thermotogales, Nitrospirales (Thermodesulfovibrio sp.) and Planctomycetales. 16S rDNA of a bacterium capable of oxidizing acetate in the course of syntrophic growth with H2-utilizing methanogens was found in high-temperature petroleum reservoirs for the first time. These results provide further insight into the composition of microbial communities of high-temperature petroleum reservoirs, indicating that syntrophic processes play an important part in acetate degradation accompanied by methane production. 相似文献
16.
Enrichment cultures inoculated with black mud fermented benzoate according to the stoichiometric equation: 4 C6H5CO2H+18 H2O 15 CH4+13 CO2.Trans-2-hydroxycyclohexanecarboxylate, 2-oxo-cyclohexanecarboxylate, pimelate, caproate, butyrate, acetate, and molecular hydrogen were shown to be regular components of the culture fluid occurring in low concentrations. Inhibition of methanogenesis by chloroform, 4-chlorobutyrate, or 2-bromooctanoate resulted in a cessation of the benzoate breakdown after all intermediates had accumulated. It is proposed that benzoate is fermented via a direct reductive pathway to butyrate, acetate, H2, and CO2, whereafter butyrate is converted to acetate and H2, and the latter substrates are fermented to CH4 and CO2 by methane producers. 相似文献
17.
In the absence of H2, Methanococcus spp. utilized pyruvate as an electron donor for methanogenesis. For Methanococcus voltae A3, Methanococcus maripaludis JJ1, and Methanococcus vannielii, typical rates of pyruvate-dependent methanogenesis were 3.4, 2.8, and 3.9 nmol min-1 mg-1 cell dry wt, respectively. These rates were 1–4% of the rates of H2-dependent methanogenesis. For M. voltae, the concentration of pyruvate required for one-half the maximum rate of methanogenesis was 7 mM, and pyruvate-dependent methanogenesis was linear for 3 days. Radiolabeled acetate was formed from [3-14C]pyruvate, and the stoichiometry of pyruvate consumed per acetate produced was 1.12±0.27. The stoichiometry of pyruvate consumed per CH4 produced was 3.64±0.34. These values are close to the expected values of 1 acetate and 4 CH4. Although 10–30% of total cell carbon could be obtained from exogenous pyruvate during growth with H2, pyruvate did not replace the nutritional requirement for acetate in Methanococcus voltae A3 or two acetate auxotrophs of Methanococcus maripaludis, JJ6 and JJ7. These results suggest that pyruvate was not oxidized in the presence of H2. The inability to oxidize pyruvate during H2-dependent methanogenesis would prevent a futile cycle of pyruvate oxidation and biosynthesis during autotrophic growth. 相似文献
18.
《Animal : an international journal of animal bioscience》2014,8(2):250-261
Concerns about the environmental effect and the economic burden of methane (CH4) emissions from ruminants are driving the search for ways to mitigate rumen methanogenesis. The use of direct-fed microbials (DFM) is one possible option to decrease CH4 emission from ruminants. Direct-fed microbials are already used in ruminants mainly to increase productivity and to improve health, and are readily accepted by producers and consumers alike. However, studies on the use of DFM as rumen CH4 mitigants are scarce. A few studies using Saccharomyces cerevisiae have shown a CH4-decreasing effect but, to date, there has not been a systematic exploration of DFM as modulators of rumen methanogenesis. In this review, we explored biochemical pathways competing with methanogenesis that, potentially, could be modulated by the use of DFM. Pathways involving the redirection of H2 away from methanogenesis and pathways producing less H2 during feed fermentation are the preferred options. Propionate formation is an example of the latter option that in addition to decrease CH4 formation increases the retention of energy from the diet. Homoacetogenesis is a pathway using H2 to produce acetate, however up to now no acetogen has been shown to efficiently compete with methanogens in the rumen. Nitrate and sulphate reduction are pathways competing with methanogenesis, but the availability of these substances in the rumen is limited. Although there were studies using nitrate and sulphate as chemical additives, use of DFM for improving these processes and decrease the accumulation of toxic metabolites needs to be explored more. There are some other pathways such as methanotrophy and capnophily or modes of action such as inhibition of methanogens that theoretically could be provided by DFM and affect methanogenesis. We conclude that DFM is a promising alternative for rumen methane mitigation that should be further explored for their practical usage. 相似文献
19.
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
20.
Marine mud volcanoes are geological structures emitting large amounts of methane from their active centres. The Amsterdam mud volcano (AMV), located in the Anaximander Mountains south of Turkey, is characterized by intense active methane seepage produced in part by methanogens. To date, information about the diversity or the metabolic pathways used by the methanogens in active centres of marine mud volcanoes is limited. (14)C-radiotracer measurements showed that methylamines/methanol, H(2)/CO(2) and acetate were used for methanogenesis in the AMV. Methylotrophic methanogenesis was measured all along the sediment core, Methanosarcinales affiliated sequences were detected using archaeal 16S PCR-DGGE and mcrA gene libraries, and enrichments of methanogens showed the presence of Methanococcoides in the shallow sediment layers. Overall acetoclastic methanogenesis was higher than hydrogenotrophic methanogenesis, which is unusual for cold seep sediments. Interestingly, acetate porewater concentrations were extremely high in the AMV sediments. This might be the result of organic matter cracking in deeper hotter sediment layers. Methane was also produced from hexadecanes. For the most part, the methanogenic community diversity was in accordance with the depth distribution of the H(2)/CO(2) and acetate methanogenesis. These results demonstrate the importance of methanogenic communities in the centres of marine mud volcanoes. 相似文献