PHYLOGENETIC DIVERSITY OF ARCHAEA IN SEDIMENT SAMPLES FROM A COASTAL SALT-MARSH

The Archaea present in salt marsh sediment samples from a tidal creek and from an adjacent area of vegetative marshland, both of which showe d active methanogenesis and sulfate reduction, were sampled by using 1 6S rRNA gene libraries created with Archaea-specific primers. None of the sequences were the same as reference sequences from cultured taxa, although some were closely related to sequences from methanogens prev iously isolated from marine sediments. A wide range of Euryarchaeota s equences were recovered, but no sequences from Methanococcus, Methanob acterium, or the Crenarchaeota were recovered. Clusters of closely rel ated sequences were common and generally contained sequences from both sites, suggesting that some related organisms were present in both sa mples. Recovery of sequences closely related to those of methanogens s uch as Methanococcoides and Methanolobus, which can use substrates oth er than hydrogen, provides support for published hypotheses that such methanogens are probably important in sulfate-rich sediments and ident ifies some likely candidates. Sequences closely related to those of me thanogens such as Methanoculleus and Methanogenium, which are capable of using hydrogen, were also discovered, in agreement with previous in hibitor and process measurements suggesting that these taxa are presen t at low levels of activity. More surprisingly, we recovered a variety of sequences closely related to those from different halophilic Archa ea and a cluster of divergent sequences specifically related to the ma rine group II archaeal sequences recently shown by PCR and probing to have a cosmopolitan distribution in marine samples.