Master of Science (MS)


Geology and Geophysics

Document Type



Defining the linkages between microbial metabolic activity and environmental geochemistry can be used to understand how carbonate dissolution in sulfidic karst systems proceeds. In Lower Kane Cave, Wyoming, sulfidic springs support taxonomically distinct microbial communities that are also associated with putative sulfur metabolisms (e.g., oxidation of reduced sulfur compounds, sulfate reduction, and sulfur disproportionation) that influence carbonate dissolution. The distribution of diverse microbial groups in other terrestrial subsurface environments is not well understood, making Lower Kane Cave ideal for study. Molecular genetics techniques were used to uncover diversity of 16S rRNA genes and bacterial soxB and aprA functional genes. Aqueous geochemistry was compared to sediment sulfur speciation based on X-ray absorption near-edge structure spectroscopy. The distribution of functional genes significantly correlated to gradients of dissolved oxygen and sulfide concentrations compared to the relative contributions of sediment elemental sulfur, either in the cyclo-octasulfur (S8) or polymeric sulfur forms. Despite Epsilonproteobacteria being the most abundant putative sulfur-oxidizing bacteria within the communities, particularly in upstream mats, Gammaproteobacteria of the order Thiothricales and Betaproteobacteria represented soxB gene diversity downstream and correlated to dissolved oxygen and stored S8. Deltaproteobacterial aprA groups, some of which could be linked to disproportionation, were almost exclusively associated with upstream mats and correlated to high sulfide concentrations, as well as to cysteine, stored sulfate, and methionine gradients within the sediments. Microbial storage of elemental sulfur in downstream mats precludes proton generation and diminishes the potential for limestone dissolution by those microbial groups, supporting that carbonate dissolution linked to microbial oxidation of reduced sulfur compounds would be expected upstream.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Engel, Annette Summers