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°C. The number of methanogens in silt samples reached 1010 cells/ml. A temperature decrease from 25 to 5°C led to a sharp decrease of methanogenesis in the silt samples. Nevertheless, methanogenesis was still significant even at 5°C. Different organic substrates, including polymeric and aromatic compounds, were degraded with methane production at 6°C. At depths of 20-40 cm the number of methanotrophic bacteria reached 1011 cells/ml. Methane oxidative activity of the microbial populations in the silt was less sensitive to the 25° to 5°C temperature decrease. Ten methanotrophic species, able to grow at 6°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).

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