Methane production from propionate by methanogenic mixed culture

Abstract The association of Desulfobulbus sp. with Methanosarcina barkeri 227 was able to produce CH₄ from propionate in the presence of sulfate, if a sufficient amount of ferrous iron was added to the media in order to trap the soluble sulfides produced from sulfate. In the absence of ferrous iron, soluble sulfides inhibited the acetoclastic reaction. Attempts to cultivate Desulfobulbus sp. with H₂-utilising methanogenic bacteria in the absence of sulfate did not succeed.     

Decrease of the hydraulic conductivity of sand columns by Methanosarcina barkeri

The extent to which a methanogen can clog sand columns was examined: two permeameters packed with clean quartz sand were sterilized, saturated with water, inoculated with Methanosarcina barkeri and percolated under upward flow conditions. After approx. 5 months, the hydraulic conductivity of the sand had decreased to 3% and 25% of the highest values measured earlier. At that point, gas-filled regions in the sand were clearly visible through the transparent walls of the permeameters, and methane bubbles were continuously released from the columns into the effluent. Scanning electron microscopy observations and biomass assays indicated that cell mass accumulation did not contribute significantly to the observed decrease of the hydraulic conductivity. This decrease was therefore attributed to pore blocking due to the entrapment of methane bubbles.D. Sanchez de Lozada and P. Baveye are with the Department of Soil, Crop and Atmospheric Sciences, Bradfield Hall, Cornell University, Ithaca, NY 13853, USA; P. Vandevivere is with the College of Marine Studies, University of Delaware, Lewes, DE 19958, USA. S. Zinder is with the Department of Microbiology, Rice Hall, Cornell University, Ithaca, NY 14853, USA.     

Inhibition of Acetoclastic Methanogenesis in Crude Oil- and Creosote-Contaminated Groundwater

Results from a series of studies of methanogenic processes in crude oil- and creosote-contaminated aquifers indicate that acetoclastic methanogenesis is inhibited near non-aqueous sources. At a crude oil-contaminated site, numbers of acetoclastic methanogens found close to crude oil were one hundred times fewer than those of hydrogen- and formate-utilizing methanogens. In laboratory toxicity assays, crude oil collected from the site inhibited methane production from acetate but not from formate or hydrogen. Toxicity assays with aqueous creosote extract completely inhibited acetate utilization over the range of tested dilutions but only mildly affected formate and hydrogen utilization. The combined results from the laboratory and field studies suggest that in methanogenic contaminated aquifers, inhibition of acetoclastic methanogenesis may lead to a buildup of acetate relative to dissolved organic carbon.     

Methanogenic activity and biomass in Holocene permafrost deposits of the Lena Delta, Siberian Arctic and its implication for the global methane budget

Permafrost environments within the Siberian Arctic are natural sources of the climate relevant trace gas methane. In order to improve our understanding of the present and future carbon dynamics in high latitudes, we studied the methane concentration, the quantity and quality of organic matter, and the activity and biomass of the methanogenic community in permafrost deposits. For these investigations a permafrost core of Holocene age was drilled in the Lena Delta (72°22′N, 126°28′E). The organic carbon of the permafrost sediments varied between 0.6% and 4.9% and was characterized by an increasing humification index with permafrost depth. A high CH₄ concentration was found in the upper 4 m of the deposits, which correlates well with the methanogenic activity and archaeal biomass (expressed as PLEL concentration). Even the incubation of core material at −3 and −6°C with and without substrates showed a significant CH₄ production (range: 0.04–0.78 nmol CH₄ h⁻¹ g⁻¹). The results indicated that the methane in Holocene permafrost deposits of the Lena Delta originated from modern methanogenesis by cold‐adapted methanogenic archaea. Microbial generated methane in permafrost sediments is so far an underestimated factor for the future climate development.     

The effects of sediment desiccation on the potential for nitrification, denitrification, and methanogenesis in an Australian reservoir

Sediments from an Australian reservoir were selected for varying degrees of in situ desiccation (i.e. non-desiccated, partially desiccated and desiccated). Sediment samples were then chemically amended with appropriate electron donors and acceptors to ascertain the effect of sediment desiccation on the potential for nitrification, denitrification, methanogenesis, and the interaction of these processes. There was no detectable nitrification in these sediments yet up to 75% of added nitrate was converted to dinitrogen. Denitrification was predominantly limited by nitrate although there was evidence of carbon co-limitation. None of the nitrogen cycle processes were notably affected by sediment desiccation. There was no flush of mineral nitrogen from desiccated sediments upon rewetting. Methanogenesis did not begin in these sediments until nitrate concentrations fell below 2.25 * 10^-5 M. Methanogenesis was always carbon limited. Methanogens were affected by sediment desiccation but were capable of recovery over time upon rewetting of sediments.     

Thermophilic Archaeal Diversity and Methanogenesis from El Tatio Geyser Field,Chile

The hydrothermal fluid chemistry at El Tatio Geyser Field (ETGF) in northern Chile suggests that biogenic CO₂–CH₄ cycling may play an important role in water chemistry, and relatively low sulfate (0.6–1 mM) and high molecular hydrogen (H₂) concentrations (67–363 nM) suggest that methanogenic Archaea are present in ETGF microbial mats. In this study, δ¹³C analysis of dissolved inorganic carbon and methane was not indicative of biogenic methane production (δ¹³C_CH4 values ranging from ?15‰ to ?5.3‰); however, methanogenic Archaea were successfully cultured from each of the hydrothermal sites sampled. Sanger sequencing using universal Archaea primers identified putative methanogenic orders with varying metabolic capabilities, including Methanobacteriales, Methanomicrobiales and Methanosarcinales.     

Molecular analysis of methanogenic archaeal communities in managed and natural upland pasture soils

Grassland management influences soil archaeal communities, which appear to be dominated by nonthermophilic crenarchaeotes. To determine whether methanogenic Archaea associated with the Euryarchaeota lineage are also present in grassland soils, anaerobic microcosms containing both managed (improved) and natural (unimproved) grassland rhizosphere soils were incubated for 28 days to encourage the growth of anaerobic Archaea. The contribution of potential methanogenic organisms to the archaeal community was assessed by the molecular analysis of RNA extracted from soil, using primers targeting all Archaea and Euryarchaeota. Archaeal RT‐PCR products were obtained from all anaerobic microcosms. However, euryarchaeal RT‐PCR products (of putative methanogen origin) were obtained only from anaerobic microcosms of improved soil, their presence coinciding with detectable methane production. Sequence analysis of excised denaturing gradient gel electrophoresis (DGGE) bands revealed the presence of euryarchaeal organisms that could not be detected before anaerobic enrichment. These data indicate that nonmethanogenic Crenarchaeota dominate archaeal communities in grassland soil and suggest that management practices encourage euryarchaeal methanogenic activity.     

Stimulation of biomethanation by Clostridium sp. PXYL1 in coculture with a Methanosarcina strain PMET1 at psychrophilic temperatures

Aim:  Bioaugumentation of low temperature biogas production was attempted by addition of cold-adapted Clostridium and a methanogen.
Methods and Results:  A psychrotrophic xylanolytic acetogenic strain Clostridium sp. PXYL1 growing optimally at 20°C and pH 5·3 and a Methanosarcina strain, PMET1, growing optimally on acetate and producing methane at 15°C were isolated from a cattle manure digester. Anaerobic conversion of xylose at 15°C with the coculture of the two strains was performed, and batch culture methane production characteristics indicated that methanogenesis occurred via acetate through 'acetoclastic' pathway. Stimulation studies were also undertaken to evaluate the effect of exogenous addition of the coculture on biogas yields at 15°C. Addition of 3 ml of PXYL1 at the rate of 12 × 10² CFU ml⁻¹ increased the biogas 1·7-fold (33 l per kg cowdung) when compared to control (19·3 l per kg cowdung) as well as increased the volatile fatty acid (VFA) levels to 3210 mg l⁻¹ when compared to 1140 mg l⁻¹ in controls. Exogenous of addition of 10 ml PMET1 inoculum at the rate of 6·8 ± 10² CFU ml⁻¹ in addition to PXYL1 served to further improve the biogas yields to 46 l kg⁻¹ as well as significantly brought down the VFA levels to 1350 mg l⁻¹.
Conclusions:  Our results suggest that the rate-limiting methanogenic step at low temperatures could be overcome and that biogas yields improved by manipulating the population of the acetoclastic methanogens.
Significance and Impact of the Study:  Stimulation of biomethanation at low temperature by coculture.     

Inhibition of Methanosarcina barkeri strain 227 by cadmium

Abstract The effect of cadmium (Cd) on methane formation from methanol and/or H₂–CO₂ by Methanosarcina barkeri was examined in a defined growth medium and in a simplified buffer system containing 50 mM Tes with or without 2 mM dithiothreitol (DTT). No inhibition of methanogenesis by high concentrations of cadmium was observed in growth medium. Similarly, little inhibition of methanogenesis by whole cells in the Tes buffer system was observed in the presence of 430 μM Cd or 370 μM mercury (Hg) with 2 mM DTT. When the concentration of DTT was reduced to 0.4 mM, almost complete inhibition of methanogenesis from H₂–CO₂ and methanol by 600 μM Cd was observed. In the absence of DTT, 150 μM Cd inhibited methanogenesis from H₂–CO₂ completely and from methanol by 97%. Methanogenesis from H₂–CO₂ was more sensitive to Cd than that from methanol.