Showing papers on "Methanogen published in 1994"

Field and laboratory studies of methane oxidation in an anoxic marine sediment: Evidence for a methanogen-sulfate reducer consortium

Abstract: Field and laboratory studies of anoxic sediments from Cape Lookout Bight, North Carolina, suggest that anaerobic methane oxidation is mediated by a consortium of methanogenic and sulfate-reducing bacteria. A seasonal survey of methane oxidation and CO2 reduction rates indicates that methane production was confined to sulfate-depleted sediments at all times of year, while methane oxidation occurred in two modes. In the summer, methane oxidation was confined to sulfate-depleted sediments and occurred at rates lower than those of CO2 reduction. In the winter, net methane oxidation occurred in an interval at the base of the sulfate-containing zone. Sediment incubation experiments suggest both methanogens and sulfate reducers were responsible for the observed methane oxidation. In one incubation experiment both modes of oxidation were partially inhibited by 2-bromoethanesulfonic acid (a specific inhibitor of methanogens). This evidence, along with the apparent confinement of methane oxidation to sulfate-depleted sediments in the summer, indicates that methanogenic bacteria are involved in methane oxidation. In a second incubation experiment, net methane oxidation was induced by adding sulfate to homogenized methanogenic sediments, suggesting that sulfate reducers also play a role in the process. We hypothesize that methanogens oxidize methane and produce hydrogen via a reversal of CO2 reduction. The hydrogen is efficiently removed and maintained at low concentrations by sulfate reducers. Pore water H2 concentrations in the sediment incubation experiments (while net methane oxidation was occurring) were low enough that methanogenic bacteria could derive sufficient energy for growth from the oxidation of methane. The methanogen-sulfate reducer consortium is consistent not only with the results of this study, but may also be a feasible mechanism for previously documented anaerobic methane oxidation in both freshwater and marine environments.

Continuous culture of Methanococcus jannaschii, an extremely thermophilic methanogen.

Abstract: Methanococcus jannaschii, an extremely thermophilic methanogen isolated from a deep-sea hydrothermal vent, was grown at 80 degrees C in continuous culture on a mineral salts medium gassed with H(2) and CO(2) at three different flow rates. The maximum specific growth rate was 0.56 h(-1), and the maximum specific methane productivity was 0.32 (mol g(-1) h(-1)). Uncoupling of growth and methane production was evidenced by an increase in teh non-growth-associated rate of methane formation, beta, with increasing gaseous input. The specific hydrogenase activity exhibited growth-assiciated behaviour at low growth rates, but showed no dependence on growth at higher growth rates. The growth dependence of hydrogenase activity is consistent with the pressure dependence of hydrogenase activity measured in previous experiments. In contrast, the specific protease activity was independent of the growth rate over the entire range of dilution rates studied. (c) 1994 John Wiley & Sons, Inc.

The fate of methanol in anaerobic bioreactors

Abstract: Methanol is an important component of certain industrial wastewaters. In anaerobic environments, methanol can be utilized by methanogens and acetogens. In wastewater treatment plants, the conversion of methanol into methane is preferred because this conversion is responsible for chemical oxygen demand (COD) removal, whereas with the formation of volatile fatty acids (VFA) little COD removal is achieved. Moreover, the accumulation of VFA can lead to reactor instability due to pH drops, in weakly buffered systems. The undesirable formation of VFA has previously been associated with the presence of trace elements and bicarbonate in the medium.This thesis investigates the environmental factors that lead to the predominance of acetogens over methanogens during anaerobic wastetewater treatment of methanol. For this purpose, batch and continuous experiment were carried out using a model medium composed of methanol and defined mineral nutrients. The main factors studied were: the effect of trace elements, the reactor pH, the bicarbonate level, and the methanol concentration in the reactor.In Chapter 1 an introductory review is given about anaerobic methylotrophic metabolism in environmental biotechnology. The natural and anthropogenic sources of methanol and other methylated compounds are outlined. In addition, the anaerobic methylotophic microorganisms and the biochemistry of methanol metabolism in methanogens and acetogens are briefly described. Finally, the previous experience in environmental biotechnology with the anaerobic biodegradation of methylotrophic substrates is reviewed. Included is a summary of the reactor types, efficiencies achieved and organic loadings applied for the treatment of wastewaters containing methanol.In Chapter 2, the effect of trace elements on the anaerobic conversion of methanol was studied. Cobalt was the only trace element tested which greatly enhanced methanogenesis from methanol. In continuous experiments, less acetate was formed in a cobalt-deprived reactor than in a cobalt supplemented reactor. These results suggested that cobalt levels could be used to prevent acetate formation from methanol. Therefore, in Chapter 3 the effect of cobalt addition for each individual trophic group was evaluated. Using specific inhibitors, specific activity and the kinetic parameters, μmax and Ks, were determined. Methylotrophic methanogens and acetogens were the only trophic group stimulated by cobalt addition, while the other trophic groups utilizing downstream intermediates, H 2 /CO 2 or acetate, were largely unaffected. At a low cobalt concentration, both methylotrophs had similar growth rates, whereas at high cobalt levels, acetogens grew slightly faster. The optimal cobalt concentration for both methylotrophic populations was around 0.05 mg · l -1 .In Chapter 4, the possibility of the anaerobic treatment of methanol without addition of any alkalinity was investigated. Methanol can successfully be converted into methane, regardless of the low pH value of alkalinity-free medium. An astonishing high specific methanogenic activity of 3.57 g COD · g -1 VSS · d -1 was evident, which enable the conversion of 13 g COD · l -1 · d -1 to methane during continuous operation at a reactor pH 4.2. A Methanosarcina- like organism was the main methanogen responsible for the conversion of methanol to methane.Chapter 5 presents the effect of inorganic carbon, alkalinity addition and reactor methanol concentration in anaerobic reactors. The results indicated that acetogenesis occurred only when exogenous bicarbonate was added, when unionized VFA accumulated and in the presence of high methanol concentrations, confirming the previously determined 60 times higher substrate affinity of methanogens.The results of this dissertation are summarized in Chapter 6. Methylotrophic methanogens will predominate over a broad pH range (4.2 to 7.2) if either the reactor methanol concentration, inorganic carbon content, or the cobalt concentration is low. Significant acetogenesis can only be expected to predominate if the reactor methanol concentration is high (>1000 mg COD · l -1 ), exogenous inorganic carbon is supplied, cobalt is available and methanogens are inhibited, e.g. by undissociated VFA. All these four conditions have to be met. Addition of moderate levels of NaHCO 3 (approximately 10-20 meq · l -1 ) were found to create such conditions if the reactor was overloaded.

A possible role for bile acid in the control of methanogenesis and the accumulation of hydrogen gas in the human colon.

Abstract: This study investigated a possible role for primary bile acid in the control of methanogenesis in the human colon. Production of hydrogen and methane was measured in anaerobic faecal cultures derived from faeces of six ‘non‐methanogenic’ and three methanogenic healthy humans. Using a sensitive technique for gas measurement, methane was detected in all faecal cultures, including those from ‘non‐methanogenic’ humans. Bile acid inhibited methanogenesis in a dose‐response fashion in the in vitro‘non‐methanogenic’ and methanogenic faecal cultures. Inhibition was significant at bile acid concentrations > 0.05%. Methanogenesis correlated with methanogen (methanogenic bacteria) numbers. If this inhibition occurs in vivo, then it would explain much of the epidemiology of non‐methanogenesis in humans. From an analysis of net hydrogen production by the faecal cultures, it is inferred that bile acid inhibits other hydrogen‐consuming bacteria in addition to methanogens. These in vitro data suggest a major role for bile acid in the accumulation of hydrogen gas in the colon. Possible links between bile acid induced accumulation of gas and irritable bowel syndrome are discussed.

Microbial characterization of thermophilic Archaea isolated from the Guaymas Basin hydrothermal vent

Abstract: Extremely thermophilic bacteria were isolated from sediments collected at the Guaymas Basin hydrothermal vent located in the Gulf of California. One isolate, (FC89) is a hydrogenotrophic methanogen with an optimal growth temperature of 85°C; this isolate appears to be closely related to the previously describedMethanococcus jannaschii. Thermophilic isolates TY and TYS are heterotrophic, sulfur-reducing archaea that differ from other thermophilic heterotrophic strains in physiological and molecular properties. Both heterotrophic isolates fermented carbohydrates and proteinaceous substrates; acetate was the primary product of carbohydrate fermentation, whereas acetate and a mix of organic acids were primary products of proteinaceous substrate fermentation. A detailed microbiological characterization of the isolates and a profile of fermentable substrates and fermentation products are described.

Fermentation studies with thermophilic Archaea in pure culture and in syntrophy with a thermophilic methanogen

Abstract: Two heterotrophic, thermophilic, sulfur-reducing archaea were isolated from the Guaymas Basin hydrothermal vent. The fermentation of proteinaceous and carbohydrate substrates was examined at 85°C for each isolate in the presence and absence of elemental sulfur and in coculture with a thermophilic methanogen. The heterotrophic isolates differed with respect to their requirement for sulfur. Both heterotrophic isolates exhibited a mixed organic acid fermentation from proteinaceous substrates; however, acetate was the sole organic acid produced from carbohydrate fermentation. In coculture fermentations with a thermophilic methanogen, the heterotrophic isolates exhibited enhanced growth and fermentation. Interspecies hydrogen transfer and elemental sulfur-reduction may be important microbial processes in deep-sea hydrothermal vent community metabolism.

Anaerobic treating method

Abstract: PURPOSE: To adjust a pH to a level suitable to an activity of methanogen with a low amount of pH adjusting agent and to efficiently execute an anaerobic treatment. CONSTITUTION: In an anaerobic treating method in which org. waste water is passed through an anaerobic reactor 1 keeping an anaerobic sludge 2 containing anaerobic microorganisms in one direction stream substantially, the pH at the vicinity of an inflow part 5 of a liq. to be treated in the anaerobic reactor 1 is measured with a pH measuring device 6, a quantity of the pH adjusting agent to be injected to the liq. to be treated from a chemical injecting pump 13 is controlled with a controlling device 14 so that this measured value may be kept at a prescribed value.

Bacterial Flora Involved in Anaerobic Digestion of Butyrate

Abstract: 酪酸を単一炭素源として用い,酪酸馴養メタン発酵汚泥から水素資化性メタン生成細菌BHM-1株を得,BHM-1株の微生物学的性状を調べ,酪酸分解菌との微生物相互の役割について微生物生態学的見地から考察した。酪酸に対するメタン発酵においてメタンの生成には2つのピークがあり,ピークIは酪酸分解菌と水素資化性メタン生成細菌との共生関係によるメタン生成,ピークIIは酢酸資化性メタン生成細菌かあるいは酢酸分解菌と水素資化性メタン生成細菌によるメタン生成であることが推察された。ピークIに着目して検討した結果,分離したBHM-1株はMethanobacterium formicicumに極めて類縁な微生物であった。酪酸分解菌とBHM-1株からなるコロニーの液体培養から,酪酸分解菌とBHM-1株での共生関係が示唆された。

Phylogenetic Diversity of Methanogen Endosymbionts of Anaerobic Ciliates

Abstract: Anaerobic environments occur widely wherever the accumulation of organic material exceeds the rate at which oxygen becomes available for its aerobic decomposition. Examples include marine and freshwater sediments, anaerobic sewage deposits, landfill sites and the guts of many animals (Fenchel and Finlay, 1991a). In these situations protozoa and ciliates in particular, survive by feeding on rich and varied prokaryote communities. Ciliates which live exclusively in anaerobic environments lack mitochondria and their metabolism is based upon fermentation and substrate level phosphorylation (Muller, 1988; Fenchel and Finlay, 1991a). Most of the anaerobic ciliates contain microbodies some of which have been shown to be capable of oxidizing pyruvate to acetate with the production of ATP, CO2 and H2. In such cases they are called hydrogenosomes (Muller, 1988). The origins of hydrogenosomes are unresolved, but in some ciliates they contain cristae and a double membrane and thus they resemble mitochondria (Finlay and Fenchel, 1989).

Mathematical model of substance active transport via cytoplasmic membrane of microbial cell along concentration gradient : scientific note

Abstract: Considering the process of methane generation by methanogenic bacteria as an example, the model describes the distribution of methane concentration inside the cell on condition that methane active transport via the cytoplasmic membrane does exist. The model can be used for the prediction and the evaluation of the methanogen cell metabolic efficiency. Besides, the results of the work can be applied in certain ecological studies when control of the substance bioconversion rate in the natural environment is not possible.