Methylomonas paludis sp. nov., the first acid-tolerant member of the genus Methylomoas, from an acidic wetland

An aerobic methanotrophic bacterium was isolated from an acidic (pH 3.9) Sphagnum peat bog in north-eastern Russia and designated strain MG30T. Cells of this strain are Gram-negative, pale-pink-pigmented, non-motile, thick rods that are covered by large polysaccharide capsules and contain an intracytoplasmic membrane system typical of type I methanotrophs. They possess a particulate methane monooxygenase enzyme (pMMO) and utilize only methane and methanol. Carbon is assimilated via the ribulose-monophosphate pathway; nitrogen is fixed via an oxygen-sensitive nitrogenase. Strain MG30T grows in a pH range of 3.8-7.3 (optimum pH 5.8-6.4) and at temperatures between 8 and 30°C (optimum 20-25°C). The major cellular fatty acids are C16:1ω5t, C16:1ω8c, C16:1ω7c, and C14:0; the DNA G+C content is 48.5 mol%. The isolate belongs to the family Methylococcaceae of the class Gammaproteobacteria and displays 94.7-96.9% 16S rRNA gene sequence similarity to members of the genus Methylomonas. However, strain MG30T differs from all taxonomically characterized members of this genus by the absence of motility, the ability to grow in acidic conditions, and low DNA G+C content. Therefore, we propose to classify this strain as a novel, acid-tolerant species of the genus Methylomonas, Methylomonas paludis sp. nov. Strain MG30T (=DSM 24973T = VKM B-2745T) is the type strain.

Methylovirgula ligni gen. nov., sp. nov., an obligately acidophilic, facultatively methylotrophic bacterium with a highly divergent mxaF gene

Two strains of Gram-negative, aerobic, non-pigmented, non-motile, rod-shaped bacteria were isolated from beech wood blocks during decay by the white-rot fungus Hypholoma fasciculare (Folman et al., 2008) and were designated strains BW863T and BW872. They are capable of methylotrophic growth and assimilate carbon via the ribulose-bisphosphate pathway. In addition to methanol, the novel isolates utilized ethanol, pyruvate and malate. Strains BW863T and BW872 are obligately acidophilic, mesophilic organisms capable of growth at pH values between 3.1 and 6.5 (with an optimum at pH 4.5-5.0) and at temperatures between 4 and 30 °C. Phospholipid fatty acid profiles of these bacteria contain unusually high amounts (about 90%) of 18:17c fatty acid, thereby resembling the profiles of Methylobacterium strains. The predominant quinone is Q-10. The DNA G+C content of novel isolates is 61.8-62.8 mol %. On the basis of 16S rRNA gene sequence identity, strains BW863T and BW872 are most closely related to the acidophilic methanotroph Methylocapsa acidiphila B2 (96.5-97 %). Comparative sequence analysis of mxaF, the gene encoding the large subunit of methanol dehydrogenase, placed the MxaF sequences of two novel strains in a cluster that is distinct from all previously described MxaF sequences of cultivated methylotrophs. The identity values between the MxaF sequences of the acidophilic isolates and the MxaF sequences from known alpha-, beta- and gammaproteobacterial methylotrophs comprised 69-75%, 61-63% and 64-67%, respectively. The data therefore suggest that strains BW863T and BW872 represent a novel genus and species of methylotrophic bacteria; the name Methylovirgula ligni gen. nov., sp. nov. is proposed, with strain BW863T (=DSM 19998T = NCIMB 14408T) as the type strain.

Methylocystis heyeri sp. nov., a novel type II methanotrophic bacterium possessing signature fatty acids of type I methanotrophs

A novel species is proposed for two strains of methanotrophic bacteria (H2T and Sakb1) isolated from an acidic (pH 4.3) Sphagnum peat bog lake (Teufelssee, Germany) and an acidic (pH 4.2) tropical forest soil (Thailand), respectively. Cells of strains H2T and Sakb1 were aerobic, Gram-negative, non-motile, straight or curved rods that were covered by large polysaccharide capsules and contained an intracytoplasmic membrane system typical of type II methanotrophs. They possessed both a particulate and a soluble methane monooxygenase and utilized the serine pathway for carbon assimilation. They were moderately acidophilic organisms capable of growth between pH 4.4 and 7.5 (optimum 5.8–6.2). The most unique characteristic of these strains was the phospholipid fatty acid profile. In addition to the signature fatty acid of type II methanotrophs (18 : 18c), the cells also contained large amounts of what was previously considered to be a signature fatty acid of type I methanotrophs, 16 : 18c. The DNA G+C contents of strains H2T and Sakb1 were 61.5 and 62.1 mol%, respectively. The 16S rRNA gene sequences possessed 96–98 % similarity to sequences of other type II methanotrophs in the genera Methylosinus and Methylocystis. 16S rRNA gene sequence and pmoA phylogeny demonstrated that the strains form a novel lineage within the genus Methylocystis. DNA–DNA hybridization values of strain H2T with Methylocystis parvus OBBPT and Methylocystis echinoides IMET 10491T were 18 and 25 %, respectively. Thus, it is proposed that these two strains represent a novel species, Methylocystis heyeri sp. nov. Strain H2T (=DSM 16984T=VKM B-2426T) is the type strain

Draft Genome Sequence of the Moderately Halophilic Methanotroph Methylohalobius crimeensis Strain 10Ki

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Draft Genomes of Gammaproteobacterial Methanotrophs Isolated from Terrestrial Ecosystems

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