The global atmospheric level of methane (CH4), the second most important greenhouse gas, is currently increasing by ∼10 million tons per year. Microbial oxidation in unsaturated soils is the only known biological process that removes CH4from the atmosphere, but so far, bacteria that can grow on atmospheric CH4have eluded all cultivation efforts. In this study, we have isolated a pure culture of a bacterium, strain MG08 that grows on air at atmospheric concentrations of CH4[1.86 parts per million volume (p.p.m.v.)]. This organism, namedMethylocapsa gorgona, is globally distributed in soils and closely related to uncultured members of the upland soil cluster α. CH4oxidation experiments and13C-single cell isotope analyses demonstrated that it oxidizes atmospheric CH4aerobically and assimilates carbon from both CH4and CO2. Its estimated specific affinity for CH4(a0s) is the highest for any cultivated methanotroph. However, growth on ambient air was also confirmed forMethylocapsa acidiphilaandMethylocapsa aurea, close relatives with a lower specific affinity for CH4, suggesting that the ability to utilize atmospheric CH4for growth is more widespread than previously believed. The closed genome ofM. gorgonaMG08 encodes a single particulate methane monooxygenase, the serine cycle for assimilation of carbon from CH4and CO2, and CO2fixation via the recently postulated reductive glycine pathway. It also fixes dinitrogen and expresses the genes for a high-affinity hydrogenase and carbon monoxide dehydrogenase, suggesting that atmospheric CH4oxidizers harvest additional energy from oxidation of the atmospheric trace gases carbon monoxide (0.2 p.p.m.v.) and hydrogen (0.5 p.p.m.v.).

A Gram-negative, rod-shaped, non-motile, non-spore forming bacterium (SV96 T ) was isolated from wetland soil near Ny-Å lesund, Svalbard. On the basis of 16S rRNA gene sequence similarity, strain SV96T was shown to belong to the Gammaproteobacteria, related to Methylobacter The genus Methylobacter was formed following the emendation of the description of the genus Methylococcus (Bowman et al., 1993), and Methylobacter species are equivalent to the similarly named group first coined by Whittenbury et al. (1970). The genus was further revised when three members of the genus Methylobacter were renamed as a new taxon Methylomicrobium (Bowman et al., 1995). At present the genus comprises the four species Methylobacter luteus (Bowman et al., 1993;Romanovskaya et al., 1978), Methylobacter whittenburyi (Bowman et al., 1993;Romanovskaya et al., 1978;Whittenbury et al., 1970) Lidstrom, 1988) and Methylobacter psychrophilus (Omelchenko et al., 1996; Tourova et al., 1999)., Methylobacter marinus (Bowman Strain SV96T was isolated from a soil core collected from a wetland near the settlement Ny-Å lesund (78 u 569 N 11 u 539 E), Svalbard, in July 1996. The soil emitted methane (Høj et al., 2005) and had a pH of 6?4. The temperature of the soil was 10 uC at the surface and 5 uC at 10 cm below the surface; the permafrost level was at 25 cm. After the fresh vegetation layer was removed, the upper 10 cm of the soil core was mixed, 2 g soil was taken and added to 10 ml nitrate mineral salt medium (NMS) (Whittenbury et al., 1970) at pH 6?8, and shaken for 10 min at 200 r.p.m. After 10 min of sedimentation, 1 ml supernatant was mixed with 9 ml NMS in a 120 ml serum bottle (Alltech). The bottle was sealed with a rubber stopper and crimp cap. Twenty millilitres of air was replaced with 20 ml CH 4 /CO 2 (95 : 5) mixture (both gases were 99?95 % purity). The bottle was incubated at 20 uC and subcultured every 2-3 weeks (1 ml culture to 9 ml fresh NMS medium). After four or five subculturing steps in liquid media, bacteria were plated on NMS medium containing 1?5 % noble agar (bacteriological agar type E; Biokar diagnostics). The plates were incubated at 20 u C in sealed chambers containing approximately 35 % methane in air. Colonies were picked and restreaked. Heterotrophic contamination was checked by streaking colonies on agar plates with rich medium containing 0?5 % tryptone, 0?25 % yeast extract, 0?1 % glucose and 2?0 % agar. These plates were incubated at room temperature without additional methane. The cultures were considered to be pure when only one cell type was observed under light microscopy and no growth on nutrient rich medium was observed. Exospore Abbreviations: PLFA, phospholipid fatty acid; RuMP, ribulose monophosphate; sMMO, soluble methane monooxygenase.

The dominant terminal process of carbon mineralization in most freshwater wetlands is methanogenesis. With methane being an important greenhouse gas, the predicted warming of the Arctic may provide a positive feedback. However, the amount of methane released to the atmosphere may be controlled by the activity of methane-oxidizing bacteria (methanotrophs) living in the oxic surface layer of wetlands. Previously, methanotrophs have been isolated and identified by genetic profiling in High Arctic wetlands showing the presence of only a few genotypes. Two isolates from Solvatnet (Ny-Ålesund, Spitsbergen; 79°N) are available: Methylobacter tundripaludum (type I) and Methylocystis rosea (type II), raising the question whether the low diversity is a cultivation effect. We have revisited Solvatnet applying stable isotope probing (SIP) with (13) C-labelled methane. 16S rRNA profiling revealed active type I methanotrophs including M. tundripaludum, while no active type II methanotrophs were identified. These results indicate that the extant M. tundripaludum is an active methane oxidizer at its locus typicus; furthermore, Methylobacter seems to be the dominant active genus. Diversity of methanotrophs was low as compared, e.g. to wetland rice fields in the Mediterranean. This low diversity suggests a high vulnerability of Arctic methanotroph communities, which deserves more attention.

The methanotrophic community in arctic soil from the islands of Svalbard, Norway (78 degrees N) was analysed by combining group-specific PCR with PCR of the highly variable V3 region of the 16S rRNA gene and then by denaturing gradient gel electrophoresis (DGGE). Selected bands were sequenced for identification. The analyses were performed with DNA extracted directly from soil and from enrichment cultures at 10 and 20 degrees C. The two genera Methylobacter and Methylosinus were found in all localities studied. The DGGE band patterns were simple, and DNA fragments with single base differences were separated. The arctic tundra is a potential source of extensive methane emission due to climatic warming because of its large reservoirs of stored organic carbon. Higher temperatures due to climatic warming can cause increased methane production, and the abundance and activity of methane-oxidizing bacteria in the arctic soil may be important regulators for methane emission to the atmosphere.

A Gram-negative, rod-shaped, non-motile, non-spore-forming, pink-pigmented bacterium, SV97T , was isolated from a wetland soil near Ny-Å lesund, Svalbard Islands, Norway (786 N). On the basis of 16S rRNA gene sequence similarity, strain SV97 T was shown to belong to the Alphaproteobacteria and was highly related to a number of non-characterized Methylocystis strains with GenBank accession nos AJ458507 and AJ458502 (100 %) and AF177299, AJ458510, AJ458467, AJ458471, AJ431384, AJ458475, AJ458484, AJ458501 and AJ458466 (99 %). The most closely related type strains were Methylocystis parvus OBBP T (97?2 %) and Methylocystis echinoides IMET 10491 T (97 %). The closest related recognized species within the genus Methylosinus wasMethylosinus sporium NCIMB 11126 T (96?0 % similarity). Chemotaxonomic and phenotypic data (C 18 : 1 v8 as the major fatty acid, non-motile, no rosette formation) supported the affiliation of strain SV97 T to the genus Methylocystis. The results of DNA-DNA hybridization and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain SV97 T from the two recognized Methylocystis species. Strain SV97 T therefore represents a novel species, for which the name Methylocystis rosea sp. nov. is proposed, with the type strain SV97 T