PHYLOGENETIC ANALYSIS OF GROUP-I MARINE ARCHAEAL RIBOSOMAL-RNA SEQUENCES EMPHASIZES THE HIDDEN DIVERSITY WITHIN THE PRIMARY GROUP ARCHAEA

Archaea form one of the three primary groups of extant life and are co mmonly associated with the extreme environments which many of their me mbers inhabit. Currently, the Archaea are classified into two kingdoms , Crenarchaeota and Euryarchaeota, based on phylogenetic analysis of r ibosomal RNA (rRNA) sequences. Molecular techniques allowing the retri eval and analysis of rRNA sequences from diverse environments are incr easing our knowledge of archaeal diversity. This report describes the presence of marine Archaea in north-east Atlantic waters. Quantitative estimates indicated that the marine Archaea constitute 8% of the tota l prokaryotic rRNA in Irish coastal waters. Phylogenetic analysis of t he archaeal rRNA gene sequences revealed sufficient genetic diversity within Archaea to indicate that the current two-kingdom classification of Crenarchaeota and Euryarchaeota is restrictive.