Showing papers on "Methanogen published in 1992"
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TL;DR: Results indicate that formate inhibited succinate oxidation to fumarate, an intermediate step in the biochemical pathway of propionate oxidation in cultures with M. thermoautotrophicum, showing that interspecies hydrogen transfer is the mechanism by which reducing equivalents are channelled from the acetogens to this methanogen.
Abstract: Thermophilic propionate-oxidizing, proton-reducing bacteria were enriched from the granular methanogenic sludge of a bench-scale upflow anaerobic sludge bed reactor operated at 55°C with a mixture of volatile fatty acids as feed. Thermophilic hydrogenotrophic methanogens had a high decay rate. Therefore, stable, thermophilic propionate-oxidizing cultures could not be obtained by using the usual enrichment procedures. Stable and reproducible cultivation was possible by enrichment in hydrogen-pregrown cultures of Methanobacterium thermoautotrophicum ΔH which were embedded in precipitates of FeS, achieved by addition of FeCl2 to the media. The propionate-oxidizing bacteria formed spores which resisted pasteurization for 30 min at 90°C or 10 min at 100°C. Highly purified cultures were obtained with either M. thermoautotrophicum ΔH or Methanobacterium thermoformicicum Z245 as the syntrophic partner organism. The optimum temperature for the two cultures was 55°C. Maximum specific growth rates of cultures with M. thermoautotrophicum ΔH were somewhat lower than those of cultures with M. thermoformicicum Z245 (0.15 and 0.19 day-1, respectively). Growth rates were even higher (0.32 day-1) when aceticlastic methanogens were present as well. M. thermoautotrophicum ΔH is an obligately hydrogen-utilizing methanogen, showing that interspecies hydrogen transfer is the mechanism by which reducing equivalents are channelled from the acetogens to this methanogen. Boundaries of hydrogen partial pressures at which propionate oxidation occurred were between 6 and 34 Pa. Formate had a strong inhibitory effect on propionate oxidation in cultures with M. thermoautotrophicum. Inhibition by formate was neutralized by addition of the formate-utilizing methanogen or by addition of fumarate. Results indicate that formate inhibited succinate oxidation to fumarate, an intermediate step in the biochemical pathway of propionate oxidation.
123 citations
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TL;DR: The substantial progress made over the past decade in understanding the molecular biology of methanogens should now provide a data base for considering genetic approaches to improving this process.
Abstract: Methanogens are a very diverse group of the Archaea (Archaebacteria). Their genomic DNAs range from 26 to 68 mol% G+C; they exhibit all known prokaryotic morphologies and inhabit anaerobic environments as varied as the human gut and deep-sea volcanic vents. They are, nevertheless, unified by their ability to gain energy by reducing CO, CO2, formate, methanol, methylamines, or acetate to methane. Methanogen genes are reviewed and analyzed in terms of their organization, structure, and expression and are compared with their bacterial (eubacterial) and eukaryal (eukaryotic) counterparts. Many methanogens are thermophiles, and some are hyperthermophiles. The influence of these extreme environments on their macromolecular structures is also addressed. Methanogens are oxygen-sensitive, fastidious anaerobes, and therefore their experimental manipulation in research laboratories has been very limited. The majority of the information currently available describing their molecular biology has been gained by gene cloning. With improvements in anaerobic handling procedures, this is beginning to change, and several experimentally tractable regulated systems of gene expression in methanogens are discussed. Anaerobic biodegradation terminating in methane biogenesis is an established, economically very important biotechnology used world-wide both to reduce waste and to generate fuel-grade biogas. The substantial progress made over the past decade, reviewed here, in understanding the molecular biology of methanogens should now provide a data base for considering genetic approaches to improving this process.
116 citations
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TL;DR: The microbial species composition of methanogenic granules developed on an acetate-propionate-butyrate mixture was characterized and sulfate-reducing bacteria did not play a significant role in the metabolism of H2, formate, acetate and butyrate but they were involved in propionate degradation.
Abstract: The microbial species composition of methanogenic granules developed on an acetate-propionate-butyrate mixture was characterized. The granules contained high numbers of adhesive methanogens (1012/g dry weight) and butyrate-, isobutyrate-, and propionate-degrading syntrophic acetogens (1011/g dry weight), but low numbers of hydrolytic-fermentative bacteria (109/g dry weight). Prevalent methanogens in the granules included: Methanobacterium formicicum strain T1N and RF, Methanosarcina mazei strain T18, Methanospirillum hungatei strain BD, and a non-filamentous, bamboo-shaped rod species, Methanothrix/Methanosaeta-like strain M7. Prevalent syntrophic acetogens included: a butyrate-degrading Syntrophospora bryantii-like strain BH, a butyrate-isobutyrate degrading non-spore-forming rod, strain IB, a propionate-degrading sporeforming oval-shaped species, strain PT, and a propionate-degrading none-spore-forming sulfate-reducing rod species, strain PW, which was able to grow syntrophically with an H2-utilizing methanogen. Sulfate-reducing bacteria did not play a significant role in the metabolism of H2, formate, acetate and butyrate but they were involved in propionate degradation.
93 citations
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TL;DR: Ciliates with methanogens produced CH4 under microaerobic conditions due to their ability to maintain an anoxic intracellular environment at low external oxygen tensions andoretical considerations suggest that hydrogen transfer is significant to the metabolism of larger anaerobic ciliates.
Abstract: Rates of methane production by three anaerobic ciliates containing symbiotic methanogens (the marine Metopus contortus and Plagiopyla frontata, and the limnic Metopus palaeformis) were quantified. Hydrogen production by normal (containing active symbionts), aposymbiotic and BES-treated cells was also measured in the case of the marine species. Methanogenesis was closely coupled to host metabolism and growth; at maximum ciliate growth rates (20°C) each methanogen produced about 1 fmol CH4 per hour corresponding to about 7, 4 and 0.35 pmol per ciliate per hour for M. contortus, P. frontata and M. palaeformis, respectively. Normal cells produced traces of H2. Hydrogen production by BES-treated or aposymbiotic cells accounted for 75 and 45% of the methane production of normal M. contortus and P. frontata cells, respectively. However, it is possible that hydrogen production was partly inhibited in the absence of methanogens. Theoretical considerations suggest that hydrogen transfer is significant to the metabolism of larger anaerobic ciliates. Ciliates with methanogens produced CH4 under microaerobic conditions due to their ability to maintain an anoxic intracellular environment at low external oxygen tensions. Methanogenesis was still detectable at a pO2 of 0.63 kPa (3 %atm sat).
66 citations
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TL;DR: Methanothrix soehngenii, a methanogen often observed in methanogenic granular sludge, was highly hydrophobic and showed low electrophoretic mobility at pH 7.5, indicating that the upflow anaerobic sludge blanket reactor concept selects for hydrophilic bacteria.
Abstract: The hydrophobicities and electrophoretic mobilities of isolates from methanogenic anaerobic granular sludge were measured and compared with those of strains from culture collections. All new isolates were highly hydrophobic, indicating that the upflow anaerobic sludge blanket reactor concept selects for hydrophobic bacteria. Methanothrix soehngenii, a methanogen often observed in methanogenic granular sludge, was highly hydrophobic and showed low electrophoretic mobility at pH 7. The role of this strain in the formation of methanogenic granular sludge is discussed.
47 citations
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TL;DR: The growth rates of ciliates and methanogens are approximately equivalent, and the only exception occurs in ciliate showing no net growth, when substrate supply within the ciliate is still sufficient to promote measurable growth of methanogenic growth.
24 citations
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TL;DR: A highly simplified anaerobic consortium which was able to degrade benzoate under mesophilic conditions was obtained from digested sludge acclimatized with Benzoate and converted 5 mM benzoates to methane quantitatively within 3 weeks in the absence of any organic nutrients under an N 2 /CO 2 atmosphere.
17 citations
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TL;DR: A system was developed for the semi-continuous cultivation of an anaerobic fungus, Piromyces sp.
Abstract: A system was developed for the semi-continuous cultivation of an anaerobic fungus, Piromyces sp. strain E2 (isolated from an Indian elephant), on Avicel (microcrystalline cellulose). The fungus was grown in a semi-continuous culture system: solids and fungal biomass was retained by means of a simple filter construction whereas the culture fluid was removed continuously. The production of fermentation products (acetate, ethanol, formate, lactate, hydrogen or methane), cellulolytic and xylanolytic enzymes, and protein by the fungus in monoculture or co-culture with Methanobacterium formicicum during growth on Avicel was monitored up to 45 days. These productions stabilized after an adaptation period of 24 and 30 days in the semi-continuous co-culture and monoculture, respectively. After this period the average (±SD) avicelase, β-glucosidase, endoglucanase, and xylanase production in the semi-continuous monoculture were 27±6, 140±16, 1057±120 and 5012±583 IU.l−1.dya−1, respectively. Co-culture with the methanogen caused a shift in fermentation products to more acetate, and less ethanol and lactate. Furthermore, the production of all cellulolytic enzymes increased (40%) and xylanolytic enzyme production decreased (35%).
14 citations
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TL;DR: Van der Heijden et al. as mentioned in this paper studied the effect of five priority pollutants in the Rhine Action Programme on Dutch river sediments, which are produced in high quantities and are relatively toxic and persistent.
Abstract: High numbers of bacteria are found in Dutch river sediments, which have a large capacity for the biodegradation of organic compounds and play an important role in the cycling of nutrients and elements. The bacteria are of vital importance in the functioning of river ecosystems. The methanogenic bacteria are responsible for the production of methane. Methanogenesis is the last stage of the anaerobic decomposition of organic matter. Without methanogen activity the degradation of organic matter cannot be carried out completely and acetic acid (and other organic acids) would accumulate. In anaerobic freshwater sediments acetate is the substrate used in about 70% of the methane production. An inhibitory effect on any of the processes carried out by the microbial consortium degrading organic matter, can lead to a decrease of methane production. The 5 toxicants used in this study are priority pollutants in the Rhine Action Programme, which are produced in high quantities and are relatively toxic and persistent. Benzene is an organic toxicant without a specific mode of action and thus exhibiting minimum toxicity. Chloroform is not very toxic under aerobic conditions. Van der Heijden quotes a value for initial reduction of cell multiplication of a Pseudomonas putida strain under aerobicmore » aqueous conditions at 125 mg/L chloroform. Under anaerobic conditions however, toxic free radicals can be formed during the reductive dechlorination of chloroform. Therefore anaerobic bacteria might be more sensitive to chloroform. The mode of action of 1,2-dichloroethane might be similar to chloroform. Pentachlorophenol is an uncoupler of the proton motive force. Zinc is known to be relatively toxic to microbial processes. Monitoring the effect of these very different pollutants on the methane production give information about the effect of these compounds on the microflora decomposing organic matter in a particular methanogenic ecosystem. 17 refs., 1 fig., 1 tab.« less
10 citations
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TL;DR: The bacterium KN-15 was the fastest-growing thermophilic rod-shaped methanogen among the isolates reported under low NaCl concentration, and had a specific growth rate of 0.62 h −1 .
5 citations
01 Jan 1992
TL;DR: Studies of tropical wetlands, including rice paddies and swamps, and the study of a variety of ruminants in the tropics are particularly interesting and appropriate at this time, with respect to methane produced in these ecosystems.
Abstract: Methane produced microbiologically is currently used as an energy source, especially by cities and industries, albeit at a level far below its potential; the incentive is currently to save money on disposal costs for waste problems. Anaerobic digestion can be helpful in degrading several halogenated hydrocarbon wastes, and methanogens are partly responsible. Ethane instead of methane may be a future product of interest. Some pure cultures of methanogens may be suitable for production of B-12, or perhaps the speciality biochemical F420, a 5-deazaflavin of interest to both methanogen and streptomyces researchers. Methanogens can cause a variety of problems, including biocorrosion, increased atmospheric methane, and ruminant nutrition loss. Studies of tropical wetlands, including rice paddies and swamps, and the study of a variety of ruminants in the tropics are particularly interesting and appropriate at this time, with respect to methane produced in these ecosystems. In some cases, it may be possible to control methane production by the use of inhibitors or ecological control mechanisms.
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TL;DR: A marine mesophilic, irregular coccoid methanogen, which shows close resemblance to Methanococcus sp.
Abstract: A marine mesophilic, irregular coccoid methanogen, which shows close resemblance toMethanococcus sp., was isolated from the biofilm of shiphulls docked in Los Angeles harbor. Hydrogen plus carbon dioxide or formate served as substrates for methanogenesis in a mineral salt medium. The isolate did not use acetate and methanol as sole source of carbon and energy. The organism had an optimal pH range of 6.8–7.0 and a temperature optimum of 37°C. Elevated levels of sodium chloride were required for optimum growth. Optimum levels of total sulfide and magnesium chloride for growth were 1.0mm and 10mm respectively. The isolate used ammonia as nitrogen source. The concentration of 30mm ammonium chloride supported maximum growth of the isolate.
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01 Jan 1992TL;DR: It is shown that the granulation process in simple mixed-cultures in an anaerobic digestion system requires three functionally different trophic groups of bacteria: hydrolytic fermentative, syntrophic acetogenic, and methanogenic bacteria.
Abstract: Application of the UASB process has been expanding for anaerobic treatment of wastewaters. In UASB reactor, the self-granulated sludge is being naturally accumulated in a high concentration(e.g., 50 g/1). Generally, the granules consist not only of microorganisms but also of inorganic matters, and vary widely in physical, chemical, and microbiological characteristics, depending on liquid velocity/ seed sludge, chemical composition of wastewaters, and so on[l]. To elucidate such complex mechanisms of granule formation, it would be necessary to analyze firstly the granulation process in simple mixed-cultures in an anaerobic digestion system. The anaerobic digestion requires three functionally different trophic groups of bacteria: hydrolytic fermentative (acidogenic), syntrophic acetogenic, and methanogenic bacteria.