Methylocapsa acidiphila gen. nov., sp nov., a novel methane-oxidizing and dinitrogen-fixing acidophilic bacterium from Sphagnum bog

A novel genus and species, Methylocapsa acidiphila gen. nov., sp. nov., are proposed for a methane-oxidizing bacterium isolated from an acidic Sphagnum peat bog. This bacterium, designated strain B2(T),represents aerobic, Gram-negative, colourless, non-motile, curved coccoids that form conglomerates covered by an extracellular polysaccharide matrix. The cells use methane and methanol as sole sources of carbon and energy and utilize the serine pathway for carbon assimilation. Strain B2(T) is a moderately acidophilic organism with growth between pH 4.2 and 7.2 and at temperatures from 10 to 30 degreesC. The cells possess a well-developed system of intracytoplasmic membranes (ICM) packed in parallel on only one side of the cell membrane. This type of ICM structure represents a novel arrangement, which was termed type III. The resting cells are Azotobacter-type cysts. Strain B2(T) is capable of atmospheric nitrogen fixation; it possesses particulate methane monooxygenase and does not express soluble methane monooxygenase. The major phospholipid fatty acid is 18:1omega7c and the major phospholipids are phosphatidylglycerols. The G+C content of the DNA is 63.1 mol%. This bacterium belongs to the alpha-subclass of the Proteobacteria and is most closely related to the acidophilic methanotroph Methylocella palustris K-T (97.3 % 16S rDNA sequence similarity). However, the DNA-DNA hybridization value between strain B2(T) and Methylocella palustris K-T is only 7 %. Thus, strain B2(T) is proposed to comprise a novel genus and species, Methylocapsa acidiphila gen. nov., sp. nov. Strain B2(T) (= DSM 13967(T) = NCIMB 13765(T)) is the type strain.