Protist genetic diversity in the acidic hydrothermal environments of Lassen Volcanic National Park, USA

We examined eukaryote genetic diversity in the hydrothermal environments of Lassen Volcanic National Park (LVNP), Northern California. We sampled hydrothermal areas of the Bumpass Hell, Sulfur Works, Devil's Kitchen, and Boiling Springs Lake sites, all of which included diverse acidic pools, mud pots, and streams with visible algal mats and biofilms. Temperatures varied from 15 to 85 degrees C and pH from 1.7 to 5.8. DNA extraction methods compared by denaturing gradient gel electrophoresis fingerprinting exhibited similar patterns, and showed limited diversity of eukaryotic small subunit (SSU) rRNA genes compared with prokaryotes. We successfully amplified eukaryotic SSU rRNA genes from most environments up to 68 degrees C. Cloned rDNA sequences reveal acidophilic protists dominate eukaryotes in LVNP hydrothermal environments. Most sites showed phototrophic assemblages dominated by chlorophytes and stramenopiles (diatoms and chrysophytes). Heterotrophic taxa, though less abundant, included diverse alveolates (ciliates), amoebae, and flagellates. Fungi were also found at most sites, and metazoans (hexapods, nematodes, platyhelminths) were sometimes detected in less acidic environments, especially in algal mats. While many cloned rDNA sequences showed 95%-99% identity to known acidophilic isolates or environmental clones from other acidic sites (Rio Tinto), sequence diversity generally declined both with decreasing pH and increasing temperature, and both were controlling physical variables on the abundance and distribution of organisms at our sites. However, a pool at 68 degrees C with pH 1.7 yielded the greatest number of distinct sequences. While some were likely contaminants from nearby cooler sites, we suggest that Lassen's acidic hydrothermal features may harbor novel protists.