FIG. 1.

Phylogenetic tree showing the affiliations of 16S rRNA gene sequences retrieved from Hydrate Ridge sediments and Black Sea microbial mats (boldface type) with selected reference sequences of the domain Archaea. Besides cultivated organisms all previously published clone sequences from methane-rich sites are included as references (at least one representative per phylogenetic group). The tree was constructed by using maximum-likelihood analysis in combination with filters excluding highly variable positions in a subset of 200 nearly full-length sequences (>1,300 bp). Partial sequences were inserted into the reconstructed tree by using parsimony criteria with global-local optimization, without allowing changes in the overall tree topology. Probe specificity is indicated by brackets. Bar = 10% estimated sequence divergence.