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Lorenson, Gregory Wade

Geology

2006

MS

To better understand the links between microbial activity and geochemical cycling, geochemical parameters and microbial ecology must be defined together in both space and time. This can be accomplished with the help of gold-amalgam microelectrodes that provide real time in situ data of a number of redox species, including species of Fe, Mn, 0, As, and S, to define the microbes' natural environment while those microbes are collected for characterization. Characterization of the microbes' natural environment provides insight into the location and sources of potential energy available to a microorganism. The complete oxidation of sulfide is a complex pathway that provides a unique opportunity to study how subtle changes in the redox kinetics of a local environment can impact the environment's microbial ecology. The gold-amalgam microelectrode can detect subtle changes in sulfur substrates available to microbes, providing the opportunity to delineate different geochemical niches. As geochemical data are collected from the environment, microbial samples are also collected for culture-based studies, helping to address how much change in the local geochemical environment is required to invoke significant changes in the overall microbial population. Yellowstone National Park is a unique place to study systems involving sulfur species because of its wide variety of springs, thermal and non-thermal, which contain elemental sulfur and products of sulfide oxidation. In 2004 electrochemical data and microbial samples were collected at Norris Geyser Basin and Gibbon Geyser Basin, in Yellowstone National Park, Wyoming, USA. Microbial samples were drawn through tubing attached to the working electrode, making sampling concurrent with electrochemical data collection.
Extensive laboratory work was conducted to determine the electrochemical signal for sulfide, polysulfide, elemental sulfur, and arsenite in natural waters. Arsenite, which has never before been quantified in situ, can now be determined and quantified with the Au-amalgam microelectrode for a wide range of pH values and temperatures down to nanomolar concentrations. Sulfide, polysulfide, and elemental sulfur can concurrently be determined in natural waters through the use of the Au-amalgam microelectrode in natural waters over a wide range of pH values and temperatures. Electrochemical signals collected from Yellowstone's hot springs were interpreted and concentrations of redox species that could not previously be defined were determined. Microbial samples collected during electrochemical data collection were cultured using substrates designed to reflect the redox chemistry of the hot spring they were removed from. PCR and T-RFLP were run to classify microbial communities cultured on these substrates. Changes to microbial community fingerprints due to culturing with different substrates yielded inconclusive results. Energetic calculations were also conducted for reactions involving the intermediate sulfur species that can now be defined in situ. Polysulfide oxidation and reduction yield significant energy that could be used by microbial communities for metabolism in Yellowstone National Parks hot springs.