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1.
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   

2.
The short-term effects of temperature on methanogenesis from acetate or CO2 in a thermophilic (58°C) anaerobic digestor were studied by incubating digestor sludge at different temperatures with 14C-labeled methane precursors (14CH3COO or 14CO2). During a period when Methanosarcina sp. was numerous in the sludge, methanogenesis from acetate was optimal at 55 to 60°C and was completely inhibited at 65°C. A Methanosarcina culture isolated from the digestor grew optimally on acetate at 55 to 58°C and did not grow or produce methane at 65°C. An accidental shift of digestor temperature from 58 to 64°C during this period caused a sharp decrease in gas production and a large increase in acetate concentration within 24 h, indicating that the aceticlastic methanogens in the digestor were the population most susceptible to this temperature increase. During a later period when Methanothrix sp. was numerous in the digestor, methanogenesis from 14CH3COO was optimal at 65°C and completely inhibited at 75°C. A partially purified Methanothrix enrichment culture derived from the digestor had a maximum growth temperature near 70°C. Methanogenesis from 14CO2 in the sludge was optimal at 65°C and still proceeded at 75°C. A CO2-reducing Methanobacterium sp. isolated from the digestor was capable of methanogenesis at 75°C. During the period when Methanothix sp. was apparently dominant, sludge incubated for 24 h at 65°C produced more methane than sludge incubated at 60°C, and no acetate accumulated at 65°C. Methanogenesis was severely inhibited in sludge incubated at 70°C, but since neither acetate nor H2 accumulated, production of these methanogenic substrates by fermentative bacteria was probably the most temperature-sensitive process. Thus, there was a correlation between digestor performance at different temperatures and responses to temperature by cultures of methanogens believed to play important roles in the digestor.  相似文献   

3.
Emissions of the greenhouse gas methane from Arctic wetlands have been studied extensively, though little is known about the ecology and community structure of methanogenic archaea that catalyze the methane production. As part of a project addressing microbial transformations of methane in Arctic wetlands, we studied archaeal communities in two wetlands (Solvatnet and Stuphallet) at Spitsbergen, Norway (78 degrees N) during two summer seasons. Directly extracted peat community DNA and enrichment cultures of methanogenic archaea were analyzed by nested PCR combined with denaturing gradient gel electrophoresis and subsequent sequencing of 16S rRNA gene fragments. Sequences affiliated with Methanomicrobiales, Methanobacteriaceae, Methanosaeta and Group I.3b of the uncultured crenarchaeota were detected at both sites. Sequences affiliated with Methanosarcina were recovered only from the site Solvatnet, while sequences affiliated with the euryarchaeotal clusters Rice Cluster II and Sediment 1 were detected only at the site Stuphallet. The phylogenetic affiliation of the recovered sequences suggested a potential of both hydrogenotrophic and acetoclastic methanogenesis at both sites. At Solvatnet, there were clear temporal trends in the archaeal community structure over the Arctic summer season. The archaeal community composition was significantly affected by factors influencing the activity of the overall bacterial community, as measured by in situ emissions of CO2. Methane emissions at both sites were influenced more by peat temperatures and thaw depth than by the archaeal community structure. Enrichment cultures for methanogenic archaea determined that most of the methanogens detected directly in peat could grow in culture at 10 degrees C. Culture based biases were indicated in later enrichment steps by the abundant growth of a Methanosarcina strain that was not detected directly in peat samples.  相似文献   

4.
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   

5.
Terephthalate (TA) is one of the top 50 chemicals produced worldwide. Its production results in a TA-containing wastewater that is treated by anaerobic processes through a poorly understood methanogenic syntrophy. Using metagenomics, we characterized the methanogenic consortium inside a hyper-mesophilic (that is, between mesophilic and thermophilic), TA-degrading bioreactor. We identified genes belonging to dominant Pelotomaculum species presumably involved in TA degradation through decarboxylation, dearomatization, and modified β-oxidation to H2/CO2 and acetate. These intermediates are converted to CH4/CO2 by three novel hyper-mesophilic methanogens. Additional secondary syntrophic interactions were predicted in Thermotogae, Syntrophus and candidate phyla OP5 and WWE1 populations. The OP5 encodes genes capable of anaerobic autotrophic butyrate production and Thermotogae, Syntrophus and WWE1 have the genetic potential to oxidize butyrate to CO2/H2 and acetate. These observations suggest that the TA-degrading consortium consists of additional syntrophic interactions beyond the standard H2-producing syntroph–methanogen partnership that may serve to improve community stability.  相似文献   

6.
Acetate oxidation in Italian rice field at 50 °C is achieved by uncultured syntrophic acetate oxidizers. As these bacteria are closely related to acetogens, they may potentially also be able to synthesize acetate chemolithoautotrophically. Labeling studies using exogenous H2 (80%) and 13CO2 (20%), indeed demonstrated production of acetate as almost exclusive primary product not only at 50 °C but also at 15 °C. Small amounts of formate, propionate and butyrate were also produced from 13CO2. At 50 °C, acetate was first produced but later on consumed with formation of CH4. Acetate was also produced in the absence of exogenous H2 albeit to lower concentrations. The acetogenic bacteria and methanogenic archaea were targeted by stable isotope probing of ribosomal RNA (rRNA). Using quantitative PCR, 13C-labeled bacterial rRNA was detected after 20 days of incubation with 13CO2. In the heavy fractions at 15 °C, terminal restriction fragment length polymorphism, cloning and sequencing of 16S rRNA showed that Clostridium cluster I and uncultured Peptococcaceae assimilated 13CO2 in the presence and absence of exogenous H2, respectively. A similar experiment showed that Thermoanaerobacteriaceae and Acidobacteriaceae were dominant in the 13C treatment at 50 °C. Assimilation of 13CO2 into archaeal rRNA was detected at 15 °C and 50 °C, mostly into Methanocellales, Methanobacteriales and rice cluster III. Acetoclastic methanogenic archaea were not detected. The above results showed the potential for acetogenesis in the presence and absence of exogenous H2 at both 15 °C and 50 °C. However, syntrophic acetate oxidizers seemed to be only active at 50 °C, while other bacterial groups were active at 15 °C.  相似文献   

7.
Low-temperature anaerobic digestion (LTAD) technology is underpinned by a diverse microbial community. The methanogenic archaea represent a key functional group in these consortia, undertaking CO2 reduction as well as acetate and methylated C1 metabolism with subsequent biogas (40 to 60% CH4 and 30 to 50% CO2) formation. However, the cold adaptation strategies, which allow methanogens to function efficiently in LTAD, remain unclear. Here, a pure-culture proteomic approach was employed to study the functional characteristics of Methanosarcina barkeri (optimum growth temperature, 37°C), which has been detected in LTAD bioreactors. Two experimental approaches were undertaken. The first approach aimed to characterize a low-temperature shock response (LTSR) of M. barkeri DSMZ 800T grown at 37°C with a temperature drop to 15°C, while the second experimental approach aimed to examine the low-temperature adaptation strategies (LTAS) of the same strain when it was grown at 15°C. The latter experiment employed cell viability and growth measurements (optical density at 600 nm [OD600]), which directly compared M. barkeri cells grown at 15°C with those grown at 37°C. During the LTSR experiment, a total of 127 proteins were detected in 37°C and 15°C samples, with 20 proteins differentially expressed with respect to temperature, while in the LTAS experiment 39% of proteins identified were differentially expressed between phases of growth. Functional categories included methanogenesis, cellular information processing, and chaperones. By applying a polyphasic approach (proteomics and growth studies), insights into the low-temperature adaptation capacity of this mesophilically characterized methanogen were obtained which suggest that the metabolically diverse Methanosarcinaceae could be functionally relevant for LTAD systems.  相似文献   

8.
Methanobacterium espanolae, an acidiphilic methanogen, required acetate for maximal growth on H2-CO2. In the presence of 5 to 15 mM acetate, at a growth pH of 5.5, the μmax was 0.05 h-1. M. espanolae consumed 12.3 mM acetate during 96 h of incubation at 35°C with shaking at 100 rpm. At initial acetate levels of 2.5 to 10.0 mM, the amount of biomass produced was dependent on the amount of acetate in the medium. 13C nuclear magnetic resonance spectra of protein hydrolysates obtained from cultures grown on [1-13C]- or [2-13C]acetate indicated that an incomplete tricarboxylic acid pathway, operating in the reductive direction, was functional in this methanogen. The amino acids were labeled with a very high degree of specificity and at greater than 90% enrichment levels. Less than 2% label randomization occurred between positions primarily labeled from either the carboxyl or methyl group of acetate, and very little label was transferred to positions primarily labeled from CO2. The labeling pattern of carbohydrates was typical for glucogenesis from pyruvate. This methanogen, by virtue of the properties described above and its ability to incorporate all of the available acetate (10 mM or lower) from the growth medium, has advantages over other microorganisms for use in the production of specifically labeled compounds.  相似文献   

9.
The marine archaebacterium Methanococcus jannaschii was studied at high temperatures and hyperbaric pressures of helium to investigate the effect of pressure on the behavior of a deep-sea thermophile. Methanogenesis and growth (as measured by protein production) at both 86 and 90°C were accelerated by pressure up to 750 atm (1 atm = 101.29kPa), but growth was not observed above 90°C at either 7.8 or 250 atm. However, growth and methanogenesis were uncoupled above 90°C, and the high-temperature limit for methanogenesis was increased by pressure. Substantial methane formation was evident at 98°C and 250 atm, whereas no methane formation was observed at 94°C and 7.8 atm. In contrast, when argon was substituted for helium as the pressurizing gas at 250 atm, no methane was produced at 86°C. Methanogenesis was also suppressed at 86°C and 250 atm when the culture was pressurized with a 4:1 mix of H2 and CO2, although limited methanogenesis did occur when the culture was pressurized with H2.  相似文献   

10.
Hydrogen partial pressures were measured in a thermophilic coculture comprised of a eubacterial rod which oxidized acetate to H2 and CO2 and a hydrogenotrophic methanogen, Methanobacterium sp. strain THF. Zinder and Koch (S. H. Zinder and M. Koch, Arch. Microbiol. 138:263-272, 1984) originally predicted, on the basis of calculations of Gibbs free energies of reactions, that the H2 partial pressure near the midpoint of growth of the coculture should be near 4 Pa (ca. 4 × 10−5 atm; ca. 0.024 μM dissolved H2) for both organisms to be able to conserve energy for growth. H2 partial pressures in the coculture were measured to be between 20 and 50 Pa (0.12 to 0.30 μM) during acetate utilization, approximately one order of magnitude higher than originally predicted. However, when ΔGf (free energy of formation) values were corrected for 60°C by using the relationship ΔGf = ΔHfTΔSHf is the enthalpy or heat of formation, ΔS is the entropy value, and T is the temperature in kelvins), the predicted value was near 15 Pa, in closer agreement with the experimentally determined values. The coculture also oxidized ethanol to acetate, a more thermodynamically favorable reaction than oxidation of acetate to CO2. During ethanol oxidation, the H2 partial pressure reached values as high as 200 Pa. Acetate was not used until after the ethanol was consumed and the H2 partial pressure decreased to 40 to 50 Pa. After acetate utilization, H2 partial pressures fell to approximately 10 Pa and remained there, indicating a threshold for H2 utilization by the methanogen. Axenic cultures of the acetate-oxidizing organism were combined with pure cultures of either Methanobacterium sp. strain THF or Methanobacterium thermoautotrophicum ΔH to form reconstituted acetate-oxidizing cocultures. The H2 partial pressures measured in both of these reconstituted cocultures were similar to those measured in the original acetate-oxidizing rod coculture. Since M. thermoautotrophicum ΔH did not use formate as a substrate, formate is not necessarily involved in interspecies electron transfer in this coculture.  相似文献   

11.
Gas hydrates deposited in subseafloor sediments are considered to primarily consist of biogenic methane. However, little evidence for the occurrence of living methanogens in subseafloor sediments has been provided. This study investigated viable methanogen diversity, population, physiology and potential activity in hydrate-bearing sediments (1–307 m below the seafloor) from the eastern Nankai Trough. Radiotracer experiments, the quantification of coenzyme F430 and molecular sequencing analysis indicated the occurrence of potential methanogenic activity and living methanogens in the sediments and the predominance of hydrogenotrophic methanogens followed by methylotrophic methanogens. Ten isolates and nine representative culture clones of hydrogenotrophic, methylotrophic and acetoclastic methanogens were obtained from the batch incubation of sediments and accounted for 0.5–76% of the total methanogenic sequences directly recovered from each sediment. The hydrogenotrophic methanogen isolates of Methanocalculus and Methanoculleus that dominated the sediment methanogen communities produced methane at temperatures from 4 to 55 °C, with an abrupt decline in the methane production rate at temperatures above 40 °C, which is consistent with the depth profiles of potential methanogenic activity in the Nankai Trough sediments in this and previous studies. Our results reveal the previously overlooked phylogenetic and metabolic diversity of living methanogens, including methylotrophic methanogenesis.Subject terms: Biogeochemistry, Biodiversity, Environmental microbiology  相似文献   

12.
A new genus and species of a nonmotile gram-negative rod, Syntrophobacter wolinii, is the first bacterium described which degrades propionate only in coculture with an H2-using organism and in the absence of light or exogenous electron acceptors such as O2, sulfate, or nitrate. It was isolated from methanogenic enrichments from an anaerobic municipal sewage digestor, using anaerobic roll tubes containing a medium with propionate as the energy source in association with an H2-using, sulfate-reducing Desulfovibrio sp. which cannot utilize fatty acids other than formate. S. wolinii produced acetate and, presumably, CO2 and H2 (or formate) from propionate. In media without sulfate and with Methanospirillum hungatei, a methanogen that uses only H2-CO2 or formate as an energy source, acetate, methane, and, presumably, CO2 were produced from propionate and only small amounts of Desulfovibrio sp. were present. Isolation in coculture with the methanogen was not successful. S. wolinii does not use other saturated fatty acids as energy sources.  相似文献   

13.
Effects of extremely high carbon dioxide (CO2) concentrations on soil microbial communities and associated processes are largely unknown. We studied a wetland area affected by spots of subcrustal CO2 degassing (mofettes) with focus on anaerobic autotrophic methanogenesis and acetogenesis because the pore gas phase was largely hypoxic. Compared with a reference soil, the mofette was more acidic (ΔpH ∼0.8), strongly enriched in organic carbon (up to 10 times), and exhibited lower prokaryotic diversity. It was dominated by methanogens and subdivision 1 Acidobacteria, which likely thrived under stable hypoxia and acidic pH. Anoxic incubations revealed enhanced formation of acetate and methane (CH4) from hydrogen (H2) and CO2 consistent with elevated CH4 and acetate levels in the mofette soil. 13CO2 mofette soil incubations showed high label incorporations with ∼512 ng 13C g (dry weight (dw)) soil−1 d−1 into the bulk soil and up to 10.7 ng 13C g (dw) soil−1 d−1 into almost all analyzed bacterial lipids. Incorporation of CO2-derived carbon into archaeal lipids was much lower and restricted to the first 10 cm of the soil. DNA-SIP analysis revealed that acidophilic methanogens affiliated with Methanoregulaceae and hitherto unknown acetogens appeared to be involved in the chemolithoautotrophic utilization of 13CO2. Subdivision 1 Acidobacteriaceae assimilated 13CO2 likely via anaplerotic reactions because Acidobacteriaceae are not known to harbor enzymatic pathways for autotrophic CO2 assimilation. We conclude that CO2-induced geochemical changes promoted anaerobic and acidophilic organisms and altered carbon turnover in affected soils.  相似文献   

14.
Methanogenesis from acetate by a rod-shaped enrichment culture grown at 60° C was found to require the presence of two organisms rather than a single aceticlastic methanogen. A thermophilic Methanobacterium which grew on H2/CO2 or formate was isolated from the enrichment. Lawns of this methanogen were used to co-isolate an acetate oxidizer in roll tubes containing acetate agar. The rod-shaped acetate oxidizer was morphologically distinct from the methanogen and did not show F420 autofluorescence. The coculture completely degraded 40 mol/ml acetate, and produced nearly equal quantities of methane, and methanogenesis was coupled with growth. The doubling time for the coculture at 60°C was 30–40 h and the yield was 2.7±0.3 g dry wt/mol CH4. Studies with 14C-labelled substrates showed that the methyl group and the carboxyl group of acetate were both converted primarily to CO2 by the coculture and that CO2 was concurrently reduced to CH4. During growth, there was significant isotopic exchange between CO2 and acetate, especially with thecarboxyl position of acetate. These results support a mechanism for methanogenesis from acetate by the coculture in which acetate was oxidized to CO2 and H2 by one organism, while H2 was subsequently used by a second organism to reduce CO2 to CH4. Since the H2 partial pressure must be maintained below 10-4 atm by the methanogen for acetate oxidation to be thermodynamically feasible, this is an example of obligate interspecies hydrogen transfer. This mechanism was originally proposed for a single organism by Barker in 1936.  相似文献   

15.
We previously described a thermophilic (60°C), syntrophic, two-membered culture which converted acetate to methane via a two-step mechanism in which acetate was oxidized to H2 and CO2. While the hydrogenotrophic methanogen Methanobacterium sp. strain THF in the biculture was readily isolated, we were unable to find a substrate that was suitable for isolation of the acetate-oxidizing member of the biculture. In this study, we found that the biculture grew on ethylene glycol, and an acetate-oxidizing, rod-shaped bacterium (AOR) was isolated from the biculture by dilution into medium containing ethylene glycol as the growth substrate. When the axenic culture of the AOR was recombined with a pure culture of Methanobacterium sp. strain THF, the reconstituted biculture grew on acetate and converted it to CH4. The AOR used ethylene glycol, 1,2-propanediol, formate, pyruvate, glycine-betaine, and H2-CO2 as growth substrates. Acetate was the major fermentation product detected from these substrates, except for 1,2-propanediol, which was converted to 1-propanol and propionate. N,N-Dimethylglycine was also formed from glycine-betaine. Acetate was formed in stoichiometric amounts during growth on H2-CO2, demonstrating that the AOR is an acetogen. This reaction, which was carried out by the pure culture of the AOR in the presence of high partial pressures of H2, was the reverse of the acetate oxidation reaction carried out by the AOR when hydrogen partial pressures were kept low by coculturing it with Methanobacterium sp. strain THF. The DNA base composition of the AOR was 47 mol% guanine plus cytosine, and no cytochromes were detected.  相似文献   

16.
The fermentation of cellulose by monocultures of Acetivibrio cellulolyticus and cocultures of A. cellulolyticus-Methanosarcina barkeri, A. cellulolyticus-Desulfovibrio sp., and A. cellulolyticus-M. barkeri-Desulfovibrio sp. was studied. The monoculture produced ethanol, acetate, H2, and CO2. More acetate and less ethanol was formed by the cocultures than by the monoculture. Acetate was utilized by M. barkeri in coculture with A. cellulolyticus after a lag period, whereas ethanol was metabolized by the sulfate reducer only under conditions of low H2 partial pressure, i.e., when cocultured with A. celluloyticus-M. barkeri or when grown together with the methanogen. Only the three-component culture carried out the rapid conversion of cellulose to CO2 and methane. Furthermore, this culture hydrolyzed the most cellulose—85% of that initially present. This amount was increased to 90% by increasing the population of M. barkeri in the triculture. Methane production was also increased, and a quicker fermentation rate was achieved.  相似文献   

17.
Methanogenesis from Sucrose by Defined Immobilized Consortia   总被引:5,自引:5,他引:0       下载免费PDF全文
A bacterial consortium capable of sucrose degradation primarily to CH4 and CO2 was constructed, with acetate as the key methanogenic precursor. In addition, the effect of agar immobilization on the activity of the consortium was determined. The primary fermentative organism, Escherichia coli, produced acetate, formate, H2, and CO2 (known substrates for methanogens), as well as ethanol and lactate, compounds that are not substrates for methanogens. Oxidation of the nonmethanogenic substrates, lactate and ethanol, to acetate was mediated by the addition of Acetobacterium woodii and Desulfovibrio vulgaris. The methanogenic stage was accomplished by the addition of the acetophilic methanogen Methanosarcina barkeri and the hydrogenophilic methanogen Methanobacterium formicicum. Results of studies with low substrate concentrations (0.05 to 0.2% [wt/vol]), a growth-limiting medium, and the five-component consortium indicated efficient conversion (40%) of sucrose carbon to CH4. Significant decreases in yields of CH4 and rates of CH4 production were observed if any component of the consortium was omitted. Approximately 70% of the CH4 generated occurred via acetate. Agar-immobilized cells of the consortium exhibited yields of CH4 and rates of CH4 production from sucrose similar to those of nonimmobilized cells. The rate of CH4 production decreased by 25% when cysteine was omitted from reaction conditions and by 40% when the immobilized consortium was stored for 1 week at 4°C.  相似文献   

18.
The diversity of microorganisms active within sedimentary rocks provides important controls on the geochemistry of many subsurface environments. In particular, biodegradation of organic matter in sedimentary rocks contributes to the biogeochemical cycling of carbon and other elements and strongly impacts the recovery and quality of fossil fuel resources. In this study, archaeal diversity was investigated along a salinity gradient spanning 8 to 3,490 mM Cl in a subsurface shale rich in CH4 derived from biodegradation of sedimentary hydrocarbons. Shale pore waters collected from wells in the main CH4-producing zone lacked electron acceptors such as O2, NO3, Fe3+, or SO42−. Acetate was detected only in high-salinity waters, suggesting that acetoclastic methanogenesis is inhibited at Cl concentrations above ~1,000 mM. Most-probable-number series revealed differences in methanogen substrate utilization (acetate, trimethylamine, or H2/CO2) associated with chlorinity. The greatest methane production in enrichment cultures was observed for incubations with salinity at or close to the native pore water salinity of the inoculum. Restriction fragment length polymorphism analyses of archaeal 16S rRNA genes from seven wells indicated that there were links between archaeal communities and pore water salinity. Archaeal clone libraries constructed from sequences from 16S rRNA genes isolated from two wells revealed phylotypes similar to a halophilic methylotrophic Methanohalophilus species and a hydrogenotrophic Methanoplanus species at high salinity and a single phylotype closely related to Methanocorpusculum bavaricum at low salinity. These results show that several distinct communities of methanogens persist in this subsurface, CH4-producing environment and that each community is adapted to particular conditions of salinity and preferential substrate use and each community induces distinct geochemical signatures in shale formation waters.  相似文献   

19.
Direct interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability of Methanosarcina barkeri to participate in DIET was evaluated in coculture with Geobacter metallireducens. Cocultures formed aggregates that shared electrons via DIET during the stoichiometric conversion of ethanol to methane. Cocultures could not be initiated with a pilin-deficient G. metallireducens strain, suggesting that long-range electron transfer along pili was important for DIET. Amendments of granular activated carbon permitted the pilin-deficient G. metallireducens isolates to share electrons with M. barkeri, demonstrating that this conductive material could substitute for pili in promoting DIET. When M. barkeri was grown in coculture with the H2-producing Pelobacter carbinolicus, incapable of DIET, M. barkeri utilized H2 as an electron donor but metabolized little of the acetate that P. carbinolicus produced. This suggested that H2, but not electrons derived from DIET, inhibited acetate metabolism. P. carbinolicus-M. barkeri cocultures did not aggregate, demonstrating that, unlike DIET, close physical contact was not necessary for interspecies H2 transfer. M. barkeri is the second methanogen found to accept electrons via DIET and the first methanogen known to be capable of using either H2 or electrons derived from DIET for CO2 reduction. Furthermore, M. barkeri is genetically tractable, making it a model organism for elucidating mechanisms by which methanogens make biological electrical connections with other cells.  相似文献   

20.
Temperature is an important factor controlling CH4 production in anoxic rice soils. Soil slurries, prepared from Italian rice field soil, were incubated anaerobically in the dark at six temperatures of between 10 to 37°C or in a temperature gradient block covering the same temperature range at intervals of 1°C. Methane production reached quasi-steady state after 60 to 90 days. Steady-state CH4 production rates increased with temperature, with an apparent activation energy of 61 kJ mol−1. Steady-state partial pressures of the methanogenic precursor H2 also increased with increasing temperature from <0.5 to 3.5 Pa, so that the Gibbs free energy change of H2 plus CO2-dependent methanogenesis was kept at −20 to −25 kJ mol of CH4−1 over the whole temperature range. Steady-state concentrations of the methanogenic precursor acetate, on the other hand, increased with decreasing temperature from <5 to 50 μM. Simultaneously, the relative contribution of H2 as methanogenic precursor decreased, as determined by the conversion of radioactive bicarbonate to 14CH4, so that the carbon and electron flow to CH4 was increasingly dominated by acetate, indicating that psychrotolerant homoacetogenesis was important. The relative composition of the archaeal community was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of the 16S rRNA genes (16S rDNA). T-RFLP analysis differentiated the archaeal Methanobacteriaceae, Methanomicrobiaceae, Methanosaetaceae, Methanosarcinaceae, and Rice clusters I, III, IV, V, and VI, which were all present in the rice field soil incubated at different temperatures. The 16S rRNA genes of Rice cluster I and Methanosaetaceae were the most frequent methanogenic groups. The relative abundance of Rice cluster I decreased with temperature. The substrates used by this microbial cluster, and thus its function in the microbial community, are unknown. The relative abundance of acetoclastic methanogens, on the other hand, was consistent with their physiology and the acetate concentrations observed at the different temperatures, i.e., the high-acetate-requiring Methanosarcinaceae decreased and the more modest Methanosaetaceae increased with increasing temperature. Our results demonstrate that temperature not only affected the activity but also changed the structure and the function (carbon and electron flow) of a complex methanogenic system.  相似文献   

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