Geochemical and biological diversity of acidic, hot springs in Lassen Volcanic National Park

We used phylogenetic approaches and chemical/physical analyses to investigate the diversity of microorganisms in geochemically distinct acidic hot springs of Lassen Volcanic National Park (LVNP) in northern California. Geochemical composition was analyzed for twelve sites within LVNP, and 16S rRNA clone libraries were prepared and analyzed for three sites (DK12 - 93.5 degrees C, pH 1.2; USW5-86.2 degrees C, pH 2.2; and SW3 -82 degrees C, pH 1.2) using universal and Archaeal-specific primers. Phylogenetic relationships of sequences were estimated using parsimony, maximum likelihood, and Bayesian methods. The geochemical composition of the features varied widely even among proximate sites having similar temperature and pH values. Acridine Orange Direct Counts indicated cell concentrations of 10(6) to 10(8) cells/ml in the sites analyzed, which is comparable to neutral pH, mesophilic environments. In contrast to similar studies of less-acidic hot springs in which members of the Bacterial order Aquificales have been shown to dominate, no Bacterial sequences were detected in any of the libraries. Using 97% sequence identity as a cutoff value, approximately 65 phylotypes were detected, many with low similarity (< 85%) to the closest database sequences. The most prevalent clones exhibited similar to 92% identity with the Crenarchaeotes Stygioglobus azoricus and Sulfolobus solfataricus, while others exhibited high similarity (similar to 97%) to Vulcanisaeta distributa. These descriptive studies will help direct cultivation efforts and aid in modeling relationships among geochemistry, temperature, pH, and microbial diversity, to investigate the role of biotic processses (and population dynamics) in the geochemistry of these systems.