Methylocella silvestris sp. nov., a novel methanotroph isolated from an acidic forest cambisol

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Abstract
Two strains of Gram-negative, aerobic, non-pigmented, non-motile, rod-shaped, methane-oxidizing bacteria were isolated from an acidic forest cambisol near Marburg, Germany, and were designated as strains BL2T and A1. These bacteria were morphologically and phenotypically similar to Methylocella palustris KT. The cells possess a highly specific bipolar appearance. They lack the intracytoplasmic membranes common to all methane-oxidizing bacteria except Methylocella, but contain a vesicular membrane system connected to the cytoplasmic membrane. A soluble methane monooxygenase was present, but no particulate methane monooxygenase could be detected. These bacteria utilize the serine pathway for carbon assimilation. Strains BL2T and A1 are moderately acidophilic, mesophilic organisms capable of growth at pH values between 4·5 and 7 (with an optimum at pH 5·5) and at temperatures between 4 and 30 °C. Compared with Methylocella palustris KT, these strains have greater tolerance of cold temperatures, dissolved salts and methanol. On the basis of 16S rRNA gene sequence identity, of species with validly published names, strain BL2T is most closely related to Methylocella palustris KT (97·3 % identity), Beijerinckia indica subsp. indica ATCC 9039T (97·1 %) and Methylocapsa acidiphila B2T (96·2 %). The DNA G+C content is 60 mol% and the major phospholipid fatty acid is 18 : 1ω7. Strain BL2T showed only 21–22 % DNA–DNA hybridization with Methylocella palustris KT. The data therefore suggest that strains BL2T and A1 represent a novel species of Methylocella; the name Methylocella silvestris sp. nov. is proposed, with strain BL2T (=DSM 15510T=NCIMB 13906T) as the type strain.

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