Linkage of high rates of sulfate reduction in Yellowstone hot springs to unique sequence types in the dissimilatory sulfate respiration pathway

Abstract

Diversity, habitat range, and activities of sulfate-reducing prokaryotes within hot springs in Yellowstone National Park were characterized using endogenous activity measurements, molecular characterization, and enrichment. Five major phylogenetic groups were identified using PCR amplification of the dissimilatory sulfite reductase genes (dsrAB) from springs demonstrating significant sulfate reduction rates, including a warm, acidic (pH 2.5) stream and several nearly neutral hot springs with temperatures reaching 89 degrees C. Three of these sequence groups were unrelated to named lineages, suggesting that the diversity and habitat range of sulfate-reducing prokaryotes exceeds that now represented in culture.

FIG. 1.

Unrooted dendrogram depicting relationships among dsrAB gene sequences. A mask of 483 amino acid positions (gaps and ambiguous residues were excluded) was created with ARB software. The backbone tree was constructed using the neighbor-joining algorithm in PAUP*. Previously published (18) sequences from SRP grown in cultures are shown in italic characters; sequences from environmental (env) and enrichment culture (enrich) clone libraries are shown in boldface. For groups for which no member grown in culture is known, the closest sequences from the GenBank database that are representative of strains not grown in culture were included in plain characters for reference. Subtrees were constructed similarly using partial sequences (162 to 273 residues) (shown with dashed lines) and added manually to the backbone tree by using a fully sequenced member as an anchor lineage. Values at nodes are bootstrap confidence values expressed as percentages of 1,000 replications. Nodes without values indicate those unsupported by a majority of tree reconstructions. Archaeoglobus profundus was used as an outgroup in all trees. Accession numbers for all sequences are in parentheses.