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A Gram-negative, aerobic, heterotrophic, non-pigmented, dimorphic prosthecate bacterium was isolated from tundra wetland soil and designated strain Z-0023 T . Cells of this strain had a dimorphic life cycle and developed a non-adhesive stalk at a site not coincident with the centre of the cell pole, a characteristic typical of representatives of the genus Asticcacaulis. A highly distinctive feature of cells of strain Z-0023 T was the presence of a conical, bell-shaped sheath when grown at low temperature. This prosthecate bacterium was a psychrotolerant, moderately acidophilic organism capable of growth between 4 and 28 6C (optimum 15-20 6C) and between pH 4?5 and 8?0 (optimum 5?6-6?0). The major phospholipid fatty acid was 18 : 1v7c and the major phospholipids were phosphatidylglycerols. The G+C content of the DNA was 60?4 mol%. On the basis of 16S rRNA gene sequence similarity, strain Z-0023 T was most closely related to Asticcacaulis biprosthecium (98 % similarity), Asticcacaulis taihuensis (98 %) and Asticcacaulis excentricus (95 %). However, low levels of DNA-DNA relatedness to these organisms and a number of distinctive features of the tundra wetland isolate indicated that it represented a novel species of the genus Asticcacaulis, for which the name Asticcacaulis benevestitus sp. nov. is proposed. The type strain is Z-0023 T (=DSM 16100 T =ATCC BAA-896 T ).

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Three strains of Gram-negative, aerobic, motile bacteria with bipolar flagella were isolated from acidic tundra wetland soils near the city of Vorkuta and from the Chukotka and Yugorsky Peninsulas and designated strains V-022T, Ch-022 and Ju-022. The cells were rod-shaped, 0.5–0.6 µm in width and 1.3–4.5 µm in length and reproduced by irregular fission. These bacteria were facultative methylotrophs that used methanol, methylamines and a wide range of other sources of carbon and energy such as sugars and polysaccharides, ethanol and amino acids. The isolates used the Calvin–Benson pathway for the assimilation of one-carbon compounds and were unable to fix nitrogen. The new strains were moderately acidophilic and psychrotolerant, capable of growth over a pH range of 4.0 to 7.8, with optimum growth at pH 5.5–6.0. Growth occurred between 4 and 30 °C (optimum 20–25 °C). The principal phospholipid fatty acid was C18 : 1ω7c. The DNA G+C content of strain V-022T was 65.2 mol%. Analysis of the 16S rRNA gene sequences revealed that all three isolates V-022T, Ch-022 and Yu-022 exhibited almost identical 16S rRNA gene sequences (99.9 % gene sequence similarity) and formed a new lineage within the class Alphaproteobacteria. The name Methylorosula polaris is suggested to accommodate this new genus and novel species with strain V-022T ( = DSM 22001T = VKM V-2485T) as the type strain of the type species.

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