A novel obligate methylamine utilizer (strain JLW8(T)), isolated from Lake Washington sediment, was characterized taxonomically. The isolate was an aerobic, Gram-negative bacterium. Cells were rod-shaped and motile by means of a single flagellum. Reproduction was by binary fission and no resting bodies were formed. Growth was observed within a pH range of 5-8.5, with optimum growth at pH 7.5. It utilized methylamine as a single source of energy, carbon and nitrogen. Methylamine was oxidized via methylamine dehydrogenase and formaldehyde was assimilated via the ribulose monophosphate cycle. The cellular fatty acid profile was dominated by C(16 : 0)omega7c and C(16 : 0) and the major phospholipid was phosphatidylethanolamine. The DNA G+C content was 54 mol%. 16S rRNA gene sequence analysis indicated that the new isolate was closely related (97-98 % similarity) to a broad group of sequences from uncultured or uncharacterized Betaproteobacteria, but only distantly related (93-96 % similarity) to known methylotrophs of the family Methylophilaceae. Strain JLW8(T) (=ATCC BAA-1282(T)=DSM 17540(T)) is proposed as the type strain of a novel species in a new genus within the family Methylophilaceae, Methylotenera mobilis gen. nov., sp. nov.