Methanotrophic Bacteria of Acidic Sphagnum Peat Bogs

Abstract

Acidic Sphagnum peat bogs cover a considerable part of the territory of Russia and are an important natural source of biogenic methane, which is formed in their anaerobic layers. A considerable portion of this methane is consumed in the aerobic part of the bog profile by acidophilic methanotrophic bacteria, which comprise the methane filter of Sphagnum peat bogs and decrease CH4 emission to the atmosphere. For a long time, these bacteria escaped isolation, which became possible only after the elucidation of the optimal conditions of their functioning in situ: pH 4.5–5.5; temperature, from 15 to 20°C; and low salt concentration in the solution. Imitation of these conditions and rejection of earlier used media with a high content of biogenic elements allowed methanotrophic bacteria of two new genera and species—Methylocella palustris and Methylocapsa acidiphila—to be isolated from the peat of Sphagnum peat bogs of European northern Russia and western Siberia. These bacteria are well adapted to the conditions in cold, acidic, oligotrophic Sphagnum peat bogs. They grow in a pH range of 4.2–7.5 with an optimum at 5.0–5.5, prefer moderate temperatures (15–25°C) and media with a low content of mineral salts (200–500 mg/l), and are capable of active dinitrogen fixation. Design of fluorescently labeled 16S rRNA–targeted oligonucleotide probes for the detection of Methylocella palustris and Methylocapsa acidiphila and their application to the analysis of sphagnum peat samples showed that these bacteria represent dominant populations of methanotrophs with a density of 105–106 cells/g peat. In addition to Methylocella and Methylocapsa populations, one more abundant population of methanotrophs was revealed (106 cells/g peat), which were phylogenetically close to the genus Methylocystis.