Investigation of the bacterial diversity of biofilms and nitrogen-fixing microorganisms in Yellowstone Lake

Yellowstone Lake occupies a large portion of Yellowstone National Park, WY and conceals within its depths many geothermal features. Though somewhat less spectacular and much less accessible, these sublacustrine hot springs, geysers, and fumaroles, like their famous terrestrial counterparts, emit fluids and gasses enriched with many chemical and mineral nutrients. Many chemical constituents of these hydrothermal inputs are biologically relevant to microbial life in Yellowstone Lake. Hydrogen sulfide, sulfate, ammonium, and many other compounds are common constituents of hydrothermal fluids and are found at varying concentrations throughout the lake These chemicals have significant effects on the chemistry, microbial ecology, nutrient cycles (e g., sulfur and nitrogen), and ecosystem function of Yellowstone Lake, and support a wide variety of microbiological habitats in which Bacteria with potentially unique niche characteristics could exploit. In order to understand these effects, the diversity of three specific Bacterial communities associated with hydrothermal emanations were examined. The first community sampled included white, film-like Bacteria observed on the surfaces of aquatic macrophytes that were directly exposed to flowing hydrothermal waters in Sedge Bay. It was hypothesized that the Bacterial community associated with the white film material differed from that of a more typical green macrophyte. Furthermore, analysis of the bacterial diversity of these white films tested the hypothesis that Thiothrix species were an important component of these communities. The second Bacterial community was observed on artificial substrata that had been submerged in the hydrothermal waters near Pelican Roost. The physical-chemical properties of substrata influence biological adhesion. Therefore, it was hypothesized that the composition of the Bacterial communities present on two different substrata (glass and polycarbonate), exposed to hydrothermal waters would differ. The gross visual similarity between the white films studied in Sedge Bay and those found on the artificial substrata in Pelican Roost led to the hypothesis that Thiothrix would be a major constituent of these Bacterial communities as well. The third community consisted of nitrogen-fixing Bacteria collected from various locations throughout Yellowstone Lake. Nitrogen limitation in Yellowstone Lake and the discovery of nitrogen-fixing Bacteria within the streams and terrestrial geothermal features of Yellowstone National Park led to the hypothesis that the hydrothermal features within Yellowstone Lake could support thermophilic, diazotrophic Bacteria. As the emanations from hydrothermal vents vary in both temperature and chemical composition, it was further hypothesized that the structure and nitrogen-fixing activity of diazotrophic communities associated with hydrothermal fluids would also vary. By employing a variety of microscopic analyses, non-culture molecular techniques, including 16S rDNA or nifH DNA and RNA amplification, sequence analysis, and culture-based physiological analyses it was demonstrated that: (1) The Bacteria coating plants in Sedge Bay were indeed composed primarily of members of the genus Thiothrix, (2) Bacteria coating artificial substrata were composed primarily of the genera Sulfurimonas and Sulfuricurvum , and some differences were observed between the Bacterial found on glass and polycarbonate substrata, and (3) Bacteria with nifH sequences related to the genera Methylocistis and Methylomonas appear to be actively participating in nitrogen-fixation within the hydrothermal vents of Yellowstone Lake. This census of the ecological distribution of microorganisms around the chemically rich hydrothermal emanations of Yellowstone Lake will promote understanding of how these bacteria interact with their environment and the role of biodiversity in this environment. With an understanding of this ecological distribution it will be possible to discern the relationship between microbial species diversity and the function of these Bacterial ecosystems in Yellowstone Lake