Three strains of obligately methylotrophic Betaproteobacteria (Z T , SP and M3) with the ribulose monophosphate pathway of C 1 assimilation are described. The isolates were strictly aerobic, Gram-stain-negative, asporogenous, motile (strains Z T and M3) or non-motile (strain SP) rods that multiplied by binary fisson, and were mesophilic and neutrophilic. All three strains utilized methanol but only strains SP and M3 utilized methylamine as carbon and energy sources. The prevailing cellular fatty acids were straight-chain saturated C 16 : 0 and unsaturated C 16 : 1 !7c acids. The major ubiquinone was Q-8. The predominant phospholipids were phosphatidylethanolamine, phosphatidylglycerol and cardiolipin. Ammonia was assimilated by glutamate dehydrogenase. The DNA G+C contents of strains Z T , SP and M3 were 51.0, 52.0 and 52.0 mol% (T m ), respectively. Levels of 16S rRNA gene sequence similarity between the three strains were very high (99.9-100 %), and they shared high levels of DNA-DNA relatedness (88-98 %). Based on 16S rRNA gene sequence analysis and DNA-DNA relatedness (19-30 %) with the type strains of the genus Methylobacillus, the novel isolates Z T , SP and M3 are classified as representing a novel species of this genus, for which the name Methylobacillus methanolivorans sp. nov. is proposed. The type strain is Z T (=VKM B-3037 T =JCM 31401 T =CCUG 68999 T ).Methylophilaceae, a family within the order Methylophilales, embraces the genera Methylophilus (type genus), Methylobacillus, Methylovorus and Methylotenera [1]. Betaproteobacterial obligate and restricted facultative methylotrophs are capable of utilizing methanol or methylamine as a sole source of carbon and energy via the ribulose monophosphate (RuMP) cycle. Because of similar morphology and metabolic organization, the main criteria used to clarify obligate methylobacteria into separate genera and species are their genomic and phylogenetic characteristics. On the other hand, members of the family are defined by some chemotaxonomic and biochemical properties, such as specific phospholipids and enzymes, which are used for the delineation of genera . In addition, another species of the genus, 'Methylobacillus rhizosphaerae', has not been validly published at the time of writing [7]. Here, we describe three novel betaproteobacterial methylotrophic strains, Z T , SP and M3, and show that they represent a novel species of the genus Methylobacillus.The novel strains were isolated from activated sludge of a drainage system of the Baikal paper mill (Irkutskaya oblast, Russia) (strain Z T ), from soil collected in St. Petersburg (Russia) (strain SP) and from municipal sewage water in Moscow (strain M3). All the strains were grown in liquid mineral medium 'K' containing (g l À1 ): KH 2 PO 4 -2.0; (NH 4 ) 2 SO 4 -2.0; MgSO 4 Á7H 2 O -0.025; NaCl -0.5; FeSO 4 Á7H 2 O -0.002, pH 7.2 and 0.5 % (v/v) CH 3 OH. The pH value was adjusted to 7.2 by adding 5 M NaOH. Solidified medium 'K' was prepared by adding 2.0 % (w/v) agar (Difco). The activated sludge (1 g...