REVISED TAXONOMY OF THE METHANOTROPHS - DESCRIPTION OF METHYLOBACTER GEN-NOV, EMENDATION OF METHYLOCOCCUS, VALIDATION OF METHYLOSINUS AND METHYLOCYSTIS SPECIES, AND A PROPOSAL THAT THE FAMILY METHYLOCOCCACEAE INCLUDES ONLY THE GROUP-I METHANOTROPHS

Numerical taxonomic, DNA-DNA hybridization, and phospholipid fatty aci d composition analyses were performed on an extensive range of methano trophic strains, including reference strains and environmental isolate s obtained from sites throughout eastern Australia. When the results o f these studies were related to the results of a study based on genomi c physicochemical properties, they clarified group I and II methanotro ph genus and species interrelationships. The group I methanotrophs wer e found to be made up of three broadly phenotypically and genotypicall y homologous clusters of species. The first group I methanotroph clust er included the carotenoid-containing species Methylomonas methanica, Methylomonas fodinarum, and Methylomonas aurantiaca. These species rep resent the true members of the genus Methylomonas. The second group I methanotroph cluster was made up of two subclusters of strains. One su bcluster included species not capable of producing resting cells and c onsisted of the species ''Methylomonas agile,'' ''Methylomonas alba,'' and Methylomonas pelagica. The other subcluster included species capa ble of forming desiccation-resistant cysts and included Methylococcus luteus, marine Methylomonas-like strains, and Methylococcus whittenbur yi. Strains designated ''Methylococcus ucrainicus'' and Methylococcus vinelandii were found to be synonyms of Methylococcus whittenburyi, wh ile Methylococcus bovis was a synonym of Methylococcus luteus. It is p roposed that these subclusters represent a new genus, Methylobacter ge n. nov. The species in the new genus are type species Methylobacter lu teus comb. nov., Methylobacter agilis sp. nov., Methylobacter albus sp . nov., nom. rev., Methylobacter marinus sp. nov., Methylobacter pelag icus comb. nov., and Methylobacter whittenburyi comb. nov. The remaini ng group I methanotrophs included the moderately thermophilic species Methylococcus capsulatus and Methylococcus thermophilus and a group of unnamed strains closely related to Methylococcus capsulatus. It is pr oposed that these species represent the true members of the genus Meth ylococcus. The group II methanotrophs consisted of two closely related groups. The first group included budding, exospore-producing strains, while the second group included nonmotile, cyst-forming strains. Thes e groups represent the genera Methylosinus and Methyocystis, which are revived here. The genus Methylosinus gen. nov., nom. rev. includes th e species Methylosinus trichosporium sp. nov., nom. rev. and Methylosi nus sporium sp. nov., nom. rev., while the genus Methylocystis gen. no v., nom. rev. includes the species Methylocystis parvus sp. nov., nom. rev. and Methylocystis echinoides sp. nov., nom. rev.