shift from acetoclastic to H2-dependent methanogenesis in a west Siberian peat bog at low pH values and isolation of an acidophilic Methanobacterium strain.

Methane production and archaeal community composition were studied in samples from an acidic peat bog incubated at different temperatures and pH values. H(2)-dependent methanogenesis increased strongly at the lowest pH, 3.8, and Methanobacteriaceae became important except for Methanomicrobiaceae and Methanosarcinaceae. An acidophilic and psychrotolerant Methanobacterium sp. was isolated using H(2)-plus-CO(2)-supplemented medium at pH 4.5.

Trophic interactions in the methanogenic microbial community of low-temperature terrestrial ecosystems.

The formation of methane in various ecosystems is due to the functioning of an anaerobic community, which combines trophically different groups of microorganisms. The methanogenic microbial community is a complex biological system, which responds to low temperatures by changes in its trophic structure resulting in redistributing matter flows. The enhanced activity of homoacetogenic bacteria at low temperature plays a significant role in this redistribution. Due to their relatively high growth rates and metabolic versatility, homoacetogens can successfully compete with fermenting bacteria and hydrogenotrophic methanogenic archaea for common substrates. The concentration of hydrogen is an important regulatory factor in the psychroactive methanogenic community. At low temperature methanogenic archaea possessing a higher affinity for hydrogen than homoacetogens provide for interspecies H2 transport in syntrophic reactions of fatty acid decomposition. The formation of a balanced community at low temperature is a longtime process. Cold terrestrial ecosystems are dominated by psychroactive (psychrotolerant) microorganisms, which can grow over a wide range of ambient temperatures.

Temperature characteristics of methanogenic archaea and acetogenic bacteria isolated from cold environments.

In most terrestrial ecosystems of boreal and northern climate zones degradation of organic matter with methane production occurs at low temperature. Two psychrophilic methanogenic archaea and four acetogenic bacteria were described until now. Recently, we isolated 12 new strains of methanogenic archaea and 3 strains of acetogenic bacteria from different natural and man-made cold environments including tundra permafrost wet land, sediments of deep lakes, silt of sludge disposal pond, pig and cattle manure digested at 6 degrees C, and an anaerobic EGSB-reactor operated at 9 degrees C. The temperature characteristics of microorganisms isolated from cold environments are discussed. All isolates are able to grow below 10 degrees C, most of them grow at such low temperature as 1 degrees C. The upper temperature limit for most growing at low temperature acetogens is 30 degrees C, and the temperature optima is 20 degrees C and below. Most isolated methanogens have temperature optima around 25 degrees C, and upper temperature limits at 30-40 degrees C. Whether microorganisms able to grow at low temperature are classified as mesophiles, psychrophiles, or psychrotrophs (psychrotolerants) is an issue of this article. We propose to modify the basic temperature definition of anaerobic microorganisms growing at low temperature.

Production and oxidation of methane at low temperature by the microbial population of municipal sludge checks situated in north-east Europe.

Methanogenic and methane-oxidizing activities of the microbial population of sewage sludge checks (Moscow and Syktyvkar regions) were studied at temperatures ranging from 5 to 25 degrees C. The number of methanogens in silt samples reached 10(10) cells/ml. A temperature decrease from 25 to 5 degrees C led to a sharp decrease of methanogenesis in the silt samples. Nevertheless, methanogenesis was still significant even at 5 degrees C. Different organic substrates, including polymeric and aromatic compounds, were degraded with methane production at 6 degrees C. At depths of 20-40 cm the number of methanotrophic bacteria reached 10(11) cells/ml. Methane oxidative activity of the microbial populations in the silt was less sensitive to the 25 degrees to 5 degrees C temperature decrease. Ten methanotrophic species, able to grow at 6 degrees C, were enriched from the Syktyvkar sludge lagoon and identified by indirect immunofluorescence. Enrichments obtained from the Syktuvkar region (62 N) contained more species of methane oxidizing bacteria able to grow at low temperature then methanogenic enrichments obtained from Moscow region (56 N).

Acetobacterium tundrae sp nov, a new psychrophilic acetogenic bacterium from tundra soil.

A new psychrophilic, anaerobic, acetogenic bacterium from the tundra wetland soil of Polar Ural is described. The organism fermented H2/CO2, formate, methanol, and several sugars to acetate as the sole end-product. The temperature range for growth was 1-30 degrees C with an optimum at 20 degrees C. The bacterium showed no growth at 32 degrees C. Cells were gram-positive, oval-shaped, flagellated rods 0.7-1.l x 1.1-4.0 microm in size when grown at 1-20 degrees C. At 25-30 degrees C, the cell size increased up to 2-3 x 10-15 microm due to a defect in cell division. The DNA G+C content of the organism was 39.2 mol%. Based upon 16S rDNA analysis and DNA-DNA reassociation studies, the organism was classified in the genus Acetobacterium as a new species, for which the name Acetobacterium tundrae sp. nov. is proposed. The type strain is Z-4493 (=DSM 9173T).

Methanogenesis at low temperatures by microflora of tundra wetland soil.

Active methanogenesis from organic matter contained in soil samples from tundra wetland occurred even at 6 degrees C. Methane was the only end product in balanced microbial community with H2/CO2 as a substrate, besides acetate was produced as an intermediate at temperatures below 10 degrees C. The activity of different microbial groups of methanogenic community in the temperature range of 6-28 degrees C was investigated using 5% of tundra soil as inoculum. Anaerobic microflora of tundra wetland fermented different organic compounds with formation of hydrogen, volatile fatty acids (VFA) and alcohols. Methane was produced at the second step. Homoacetogenic and methanogenic bacteria competed for such substrates as hydrogen, formate, carbon monoxide and methanol. Acetogens out competed methanogens in an excess of substrate and low density of microbial population. Kinetic analysis of the results confirmed the prevalence of hydrogen acetogenesis on methanogenesis. Pure culture of acetogenic bacteria was isolated at 6 degrees C. Dilution of tundra soil and supply with the excess of substrate disbalanced the methanoigenic microbial community. It resulted in accumulation of acetate and other VFA. In balanced microbial community obviously autotrophic methanogens keep hydrogen concentration below a threshold for syntrophic degradation of VFA. Accumulation of acetate- and H2/CO2-utilising methanogens should be very important in methanogenic microbial community operating at low temperatures.