Summary auto-generated
Methylocapsa acidiphila gen. nov., sp. nov. is a novel methane-oxidizing, nitrogen-fixing bacterium isolated from an acidic Sphagnum peat bog in West Siberia. Strain B2T is a Gram-negative, curved coccoid that grows on methane and methanol as sole carbon sources, using the serine pathway for carbon assimilation. The bacterium is moderately acidophilic, growing optimally at pH 5.0–5.5 and temperatures around 20°C. It possesses a unique type III arrangement of intracytoplasmic membranes packed on one side of the cell membrane and forms Azotobacter-type cysts as resting cells. The organism contains particulate methane monooxygenase but lacks soluble methane monooxygenase, and can fix atmospheric nitrogen under both aerobic and microaerobic conditions. Phylogenetically, strain B2T belongs to the α-subclass of Proteobacteria and is most closely related to Methylocella palustris (97.3% 16S rDNA similarity), but DNA-DNA hybridization reveals only 7% relatedness, warranting designation as a distinct genus and species with a DNA G+C content of 63.1 mol%.
Key findings
- Methylocapsa acidiphila is a novel genus and species of acidophilic methanotroph with unique type III intracytoplasmic membrane arrangement packed on only one side of the cell
- The bacterium possesses particulate methane monooxygenase but not soluble methane monooxygenase, distinguishing it from most other methanotrophs
- Strain B2T can fix atmospheric nitrogen and utilizes the serine pathway for carbon assimilation from methane and methanol
- Despite 97.3% 16S rRNA similarity to Methylocella palustris, only 7% DNA-DNA hybridization confirms M. acidiphila as a separate genus
- The major phospholipid is phosphatidylglycerol (63%), differing significantly from Methylocella palustris, which is dominated by phosphatidylmethylethanolamine
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Abstract
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 degrees C. 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.