Methanogenesis from main methane precursors H(2)/CO(2) and acetate was investigated in a temperature range of 2-70 degrees C using sediments from Lake Baldegg, Switzerland. Psychrophilic, psychrotrophic, mesophilic, and thermophilic methanogenic microbial communities were enriched by incubations for 1-3 months of nonamended sediment slurries at 5, 15, 30, and 50 degrees C. Isotope experiments with slurries amended with (14)C-labeled bicarbonate and (14)C-2-acetate showed that in the psychrophilic community (enriched at 5 degrees C), about 95% of methane originated from acetate, in contrast to the thermophilic community (50 degrees C) where up to 98% of methane was formed from bicarbonate. In the mesophilic community (30 degrees C), acetate was the precursor of about 80% of the methane produced. When the hydrogen-carbon dioxide mixture (H(2)/CO(2)) was used as a substrate, it was directly converted to methane under thermophilic conditions (70 and 50 degrees C). Under mesophilic conditions (30 degrees C), both pathways, hydrogenotrophic and acetoclastic, were observed. At low temperatures (5 and 15 degrees C), H(2)/CO(2) was converted into methane by a two-step process; first acetate was formed, followed by methane production from acetate. When slurries were incubated at high partial pressures of H(2)/CO(2), the high concentrations of acetate produced of more than 20 mM inhibited acetoclastic methanogenesis at a temperature below 15 degrees C. However, slow adaptation of the psychrophilic microbial community to high acetate concentrations was observed.

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Large landfills in the Soviet Union cover more than 140 thousand hectares. The gas emission intensities are extremely disproportional over the surface of these landfills. According to our data the rates of streams of the biogas components vary from 0 till 20, 46, 1.2 and 0.75 (×10−4m3 × hour −1/m2) for CH4, CO2, H2, CO, respectively. The stable carbon isotope composition of methane and carbon dioxide in the biogas of deep landfills layers is typical for methanogenesis from organic wastes, but it depends on the concentration of organic substance in the landfill ground and on the age of these landfills. In the upper layer methane becomes heavier and carbon dioxide lighter due to the microbiological oxidation processes. The most intensive methanogenesis is usually observed in the upper part of the anaerobic zone where the organic substance concentration is relatively high. The methanogenic microflora is represented by mesophilic methanobacteria, species of Methanosarcina and Methanobacterium genera are prevalent forms. At the depth of 10-100 cm from the surface intensive oxidation of methane, hydrogen and carbon monoxide is observed. The number of gas oxidizing bacteria is up to 10 cells per gram of soil. 14 species of methane oxidizing bacteria, which belong to 5 genera were iden tified. Hydrogen oxidizing bacteria belong to Alcaligenes,Pseudomonas, Paracoccus, Mycobacteriun genera. Between them psychrotrophic forms were found. It has been shown that in small landfills methane, produced in anaerobic zone, can be oxidized completely in the upper ground layer. The biogas extraction from landfills is important not only as an additional fuel source, but as a means of preventing pollution of the Earth's atmosphere.

The enumeration of methanotrophic bacteria in the cover soil of an aged municipal landfill was carried out using (1) fluorescent in situ hybridization (FISH) with horseradish peroxidase-labeled oligonucleotide probes and tyramide signal amplification, also known as catalyzed reporter deposition-FISH (CARD-FISH), and (2) most probable number (MPN) method. The number of methanotrophs was determined in cover soil samples collected during April-November 2003 from a point with low CH(4) emission. The number of types I and II methanotrophs obtained by CARD-FISH varied from 15 +/- 2 to 56 +/- 7 x 10(8) cells g(-1) absolute dry mass (adm) of soil and methanotrophs of type I dominated over type II. The average number of methanotrophs throughout the cover soil profile was highest during May-September when the cover soil temperature was above 13 degrees C. Methanotrophs accounted for about 50% of the total bacterial population in the deepest cover soil layer owing to higher availability of substrate (CH(4)). A lower number of methanotrophs (7 x 10(2) to 17 x 10(5) cells g(-1) adm of soil) was determined by the MPN method compared to the CARD-FISH counts, thus confirming previous results that the MPN method is limited to the estimation of the culturable species that can be grown under the incubation conditions used. The number of culturable methanotrophs correlated with the methane-oxidizing activity measured in laboratory assays. In comparison to the incubation-based measurements, the number of methanotrophs determined by CARD-FISH better reflected the actual characteristics of the environment, such as release and uptake of CH(4), temperature, and moisture, and availability of substrates.

Landfills and dumps are important sources of atmospheric methane. There is no generally accepted estimate of the influence of methane oxidation on landfill methane emissions. The present work aimed to analyse different methods for the investigation of methane emission and oxidation in methane-producing environments (wetlands, landfills, sludge checks), and to develop the precise procedure for the landfills. The combination of geochemical and microbiological methods to estimate and monitor the oxidation and emission of methane in landfills during different seasons is proposed. It includes the measurements, both on the surface and at different depths (up to 1 m) of landfill ground of the following parameters: (1) concentrations of methane, carbon dioxide and oxygen; (2) quantity of 13C isotope in gas samples; (3) methane-oxidation activity of landfill grounds assayed with two different methods: (a) in conditions of no moisture or substrate limitations, and (b) in conditions with a minimal deviation to in situ conditions; (4) the density of methanotrophic microbial population.