In recent years, the study of microbial food webs in extreme environments has garnered attention from ecologists and microbiologists interested in uncovering new ecological paradigms through the examination of species-poor food webs. This project combines expertise in prokaryotic, viral, and eukaryotic biology from three institutions to investigate the food web in Boiling Springs Lake (BSL) – a stable, acidic (pH 2.2), hydrothermal (52C), 13,000m2 lake in Lassen Volcanic National Park, CA.We seek to characterize this unique ecosystem and initiate an investigation of the trophic structure in BSL as it relates to biotic and abiotic factors. BSL is a high sulfate, low chloride, low metal system in a relatively accessible, yet pristine location.

Preliminary work indicates that BSL’s conditions are extreme enough to limit genetic diversity, while allowing a complete microbial community and restricting the growth of metazoans. Prokaryotes in BSL sediments include numerous Bacterial and Archaeal genera, but appear to be dominated by three distinct phylotypes of Archaea that share less than 85% rRNA sequence identity with known organisms, and a Bacterial phylotype that shares ~ 88% rRNA sequence identity with Desulfotomaculum. Algae (especially Cyanidiales) and fungi appear to dominate the planktonic eukaryotic community. Virus-like particles are present at approximately 103 ml-1, much lower than in other environments. Additionally, geothermal inputs (up to 95C) at one end of the lake create gradients of pH, temperature, and geochemistry, and provide additional habitats for microbial consortia.

Following investigation of lake bathymetry and physical structure (using a remotely operated vehicle designed and operated by undergraduate engineering students), we propose to sample two thermally distinct regions of BSL, at various time intervals throughout the project duration, for biological and chemical analyses to assess temporal variation in the measured parameters. Standard methods will be modified for BSL to determine productivity (primary and heterotrophic), and the relative contributions of chemosynthesis and photosynthesis to primary production. Culture-independent and culture-dependent approaches will be used to identify the primary producers and to determine the abundance, distribution, and genetic diversity of prokaryotes, eukaryotes and viruses. Interactions between viruses and microbial cells will be analyzed in microcosms experiments in order to assess the potential importance of top-down controls on their abundance and diversity.

Intellectual merit – This interdisciplinary study will address the following critical questions:

• What is the physical and chemical structure of the lake, and how does it vary temporally?
• Who are the prokaryotes, eukaryotes, and viruses present in two thermally distinct regions of the lake? How do these populations change over time?
• What is the relative contribution of primary production by chemosynthesis vs. photosynthesis, and who are the potential primary producers in the lake? What are the major bottom-up controls on primary production? Is heterotrophic production driven primarily by allochthonous or autochthonous carbon?
• Do viruses and/or heterotrophic protists limit abundance of prokaryotes and eukaryotes? What is the impact of top-down control on prokaryotic and eukaryotic diversity?
  

Broader implications- A major goal of this work is to introduce undergraduates from three institutions to microbial ecology and train them in scientific research. During the next few years, we will integrate this work into 5 classes impacting > 700 undergraduate students, and an additional 100 undergraduates will be directly involved in BSL-related research projects. Our project will also contribute to graduate student training.

We are beginning to develope a web-based database of our results for the science community and public. In addition, we will involve students in producing a color booklet for LVNP visitors, highlighting the structure, chemistry, and biology of this unique lake, and giving the public a deeper appreciation of the microbial world.

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