The prokaryotic diversity of aerobic and anaerobic bacterial isolates and of bacterial and archaeal 16S rDNA clones was determined for a microbial mat sample from the moated region of Lake Fryxell, McMurdo Dry Valleys, Antarctica. Among the anaerobic bacteria, members of Clostridium estertheticum and some other psychrotolerant strains dominated whereas methanogens and other Archaea were lacking. Isolates highly related to Flavobacterium hibernum, Janthiniobacterium lividum, and Arthrobacter flavus were among the aerobic bacteria most frequently isolated. Assessment of more than 350 partial 16S rDNA clone sequences of libraries generated by Bacteria- and Archaea-specific PCR primers revealed a rich spectrum of bacterial diversity but only two different archaeal clone sequences. Among the Bacteria, representative sequences belonged to the class Proteobacteria, order Verrucomicrobiales, class Actinobacteria, Clostridium/Bacillus subphylum of Gram-positives, and the Cytophaga-Flavobacterium-Bacteroides phylum. The clones formed about 70 higher taxonomy groups (<98% sequence similarity) and 133 potential species, i.e., groups of clones sharing greater than 98% similarity. Only rarely were clone sequences found to be highly related to Lake Fryxell isolates and to strains of described species. Subsequent analysis of ten sequencing batches of 36 individual clones indicated that the diversity might be still higher than had been assessed.

Reclassification of 101 96), was isolated from a butyratedegrading, fluidized bed reactor and characterized. Cells of both species are mesophilic, highly irregular cocci that use HJCO, and formate for growth and methanogenesis. In addition, Methanogenium liminatans strains GKZPZT and B M I used 2-propanol/C02, 2-butanol/C02 and cyclopentanol/CO,. Both species contained diether and tetraether lipids. The polar lipids comprised aminophosphopentanetetrol derivatives, which appear to be characteristic I ipids within the family Methanomicrobiaceae. The pattern of glycolipids, phosphoglycolipids and amino-phosphoglycol ipids was consistent with the assignment of these two species to a taxon within the family Methanomicrobiaceae, but also permitted them to be distinguished from other higher taxa within this family. The G+C contents of the DNA of Methanogenium tationis and Methanogenium liminatans were 54 and 60 mol0h (T, and HPLC), respectively. On the basis of the data presented, the transfer of Methanogenium tationis and Methanogenium liminatans t o the genus Methanofollis gen. nov. as Methanofollis tationis comb. nov. and Methanofollis liminatans comb. nov., respectively, i s proposed, with Methanofollis tationis as the type species.

The phylogenetic position of Gram-negative, strictly anaerobic, non-sporeforming bacteria, representing four different genera, was determined by analysis of their 165 rDNA sequences. Formivibrio citricus and Propionivibrio dicarboxylicus are members of the /I-subclass of the class Proteobacteria. While Formivibrio citricus stands p h y I og ene t ica I I y is0 la ted, Propionivibrio dicarboxylicus is moderately related to members of the genus Rhodocyclus. Succinimonas amylolytica and Succinivibrio dextrinosolvens are members of the y-subclass of the class Proteobacteria in which they, together with members of the genus Anaerobiospirillum and Ruminobacter amylophilus, form a separate line of descent. This phylogenetic group is described as Succinivibrionaceae fam. nov.