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Project Progress

Our primary research objective is to better understand the origins and adaptive radiation of an ancient and biogeochemically significant assemblage of microorganisms, the sulfate-reducing prokaryotes (SRP). In overview, in the last year we have:

• Refined our understanding of energy sources sustaining SRP in geothermal habitats
• Continued to explore the diversity and distribution of SRP in habitats possibly similar to those that existed on early earth (microbial mats and hot springs).
• Developed improved methods for resolving the evolutionary history and diversity of SRP (Wagner, Loy et al. 2005; Stahl, Loy et al. In review)

Energy Sources on Early Earth. Continued studies examined the importance of alternative electron donors to sulfate respiration in hot springs within Yellowstone National Park by measuring the stimulation of sulfate reduction by exogenous substrate addition (lactate, acetate, hydrogen). In 2005, we retuned to four hot spring systems where we had previously measured significant SRR: Obsidian Pool (OP) in the Mud Volcano area, Black Sediment Pool (BSP) in the Nymph Creek area and two unnamed hot springs (SHO2 and SHO6) in the Shoshone Geyser Basin. We observed significant stimulation of SRR by hydrogen at OP and BSP, and significant stimulation of SRR by hydrogen at SHO2 but not SHO6. These findings suggest that hydrogen may be an important source of energy for endogenous sulfate reducing microorganisms in these hot spring systems. This hypothesis is supported by our efforts at cultivating sulfate reducers from these environments. Together, these results confirmed the presence of sulfate respiring microbiota that might have been sustained within geothermal systems of an early Earth (Köenneke, de la Torre et al. 2004; Köenneke, de la Torre et al. In preparation)

Microbial Mat Community. We currently have three papers in preparation from Astrobiology funded work on the microbial mat communities in Guerrero Negro, MX and Yellowstone National Park, WY. This research was performed during Dr. Dillon’s post-doctoral fellowship in Dr. Stahl’s lab at the University of Washington, in collaboration with members of the EMERG group coordinated by Drs. David Des Marais, Tori Hoehler, Brad Bebout and others at NASA Ames Research Center. These three manuscripts all relate to work investigating the diversity and biogeochemical activity of microbial mats. These modern mats are currently found in extreme environments such as the hypersaline ponds and hot spring that we have studied. From an astrobiological perspective, these mats also serve as modern analogs of some of the earliest complex communities on Earth. By improving understanding of the spatial and temporal dynamics of the sulfate-respiring bacteria in relationship to other populations (Dillon, Miller et al. In preparation; Dillon, Fishbain et al. In preparation; Dillon, Miller et al. Revision in preparation), we have contributed to a better understanding of the relationship between population structure and biogeochemistry of these analogs of early earth communities.

Technology Advances. We have contributed to two general manuscripts describing the development and application of molecular methods to better resolve the natural diversity and evolutionary history of sulfate respiring microbiota (Wagner, Loy et al. 2005; Stahl, Loy et al. In review).