The phylogenetic position of the family Methylococcaceae.

The 16S ribosomal DNA-based phylogenetic positions of various members of the Methylococcaceae (group I methanotrophs) were investigated. The Methylococcaceae as a whole formed a distinct branch in the gamma subdivision of the Proteobacteria, and this branch had five distinct subbranches. On the basis of a number of phenotypic traits, phospholipid fatty acid patterns, and the results of a 16S ribosomal DNA analysis, we determined that the species belonging to one subbranch, Methylobacter albus, Methylobacter agilis, and Methylobacter pelagicus, formed a distinct group that could be differentiated from other members of the genus Methylobacter, which grouped in an adjacent subbranch. We propose that these species belong to a new taxon, Methylomicrobium gen. nov.