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 beechwood blocks during decay by the white-rot fungus Hypholoma fasciculare 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 3.1–6.5 (with an optimum at pH 4.5–5.0) and at 4–30 °C. Phospholipid fatty acid profiles of these bacteria contain unusually large amounts (about 90 %) of C18 : 1 ω7c, thereby resembling the profiles of Methylobacterium strains. The predominant quinone is Q-10. The DNA G+C content of the novel isolates is 61.8–62.8 mol%. On the basis of 16S rRNA gene sequence similarity, strains BW863T and BW872 are most closely related to the acidophilic methanotroph Methylocapsa acidiphila B2T (96.5–97 %). Comparative sequence analysis of mxaF, the gene encoding the large subunit of methanol dehydrogenase, placed the MxaF sequences of the two novel strains in a cluster that is distinct from all previously described MxaF sequences of cultivated methylotrophs. The identity between the MxaF sequences of the acidophilic isolates and those from known alpha-, beta- and gammaproteobacterial methylotrophs was respectively 69–75, 61–63 and 64–67 %. The data therefore suggest that strains BW863T and BW872 represent a novel genus and species of methylotrophic bacteria, for which the name Methylovirgula ligni gen. nov., sp. nov. is proposed. Strain BW863T (=DSM 19998T =NCIMB 14408T) is the type strain of Methylovirgula ligni.