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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 …