Classification of halo(alkali)philic and halo(alkali)tolerant methanotrophs provisionally assigned to the genera Methylomicrobium and Methylobacter and emended description of the genus Methylomicrobium.

The taxonomic positions of four aerobic, obligately halo(alkali)philic/-tolerant, methanotrophic bacteria previously affiliated with the genera Methylobacter ('Methylobacter alcaliphilus' strains 20Z and 5Z) and Methylomicrobium (Methylomicrobium strains AMO1 and NI) were investigated. Phylogenetic analysis of 16S rRNA gene sequences indicated that the strains form a separate branch within the type I methanotrophic bacteria and are closely related to Methylomicrobium pelagicum. DNA-DNA hybridization data revealed relatively low levels of relatedness of Methylomicrobium sp. AMO1 and Methylomicrobium sp. N1 with each other and with previously described species of the genera Methylomicrobium and Methylobacter (<55 %), indicating that they may represent novel species. Based on the results presented here and on previously reported morphological and physiological characteristics, we classify these halotolerant and halophilic methanotrophic strains as representing novel species within the genus Methylomicrobium: Methylomicrobium alcaliphilum sp. nov. (type strain 20Z(T) =VKM B-2133(T) =NCIMB 14124(T); reference strain 5Z =VKM B-2180), Methylomicrobium japanense sp. nov. (type strain NI(T) =VKM B-2462(T) =FERM BP-5633(T) =NBRC 103677(T)) and Methylomicrobium kenyense sp. nov. (type strain AMO1(T) =NCCB 97157(T) =NCIMB 13566(T) =VKM B-2464(T)). The genus Methylomicrobium has been emended in its description.