Graduation Year

2020

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Cell Biology, Microbiology, Molecular Biology)

Major Professor

James Garey, Ph.D.

Committee Member

Kathleen Scott, Ph.D.

Committee Member

Diane TeStrake, Ph.D.

Keywords

16S rDNA, San Salvador, microbial ecology, photosynthesis

Abstract

This study used 16S rDNA metagenomics and water chemistry to conduct an examination of microbial community dynamics and biogeochemistry in three physically adjacent, sunlit blue holes with variable hydrologic regimes on San Salvador Island, Bahamas. Church and Watling’s Blue Holes are holomictic with relatively clear waters, while Inkwell Blue Hole hosts density stratification and waters stained brown with tannins. Based on water color and clarity and physicochemical profiles, I hypothesized Church and Watling’s Blue Holes would be dominated by oxigenic photoautotrophs, and that the bottom layer of Inkwell would be characterized by euxinic (anoxic and sulfidic) conditions and host primarily sulfur-reducing bacteria. Microbial community profiles were dominated by 16S sequences associated with photoheterotrophic organisms in Watling’s and with anoxygenic purple sulfur bacteria in Church. Communities in the surface and halocline of Inkwell were dominated by sequences affiliated with cyanobacteria and photoheterotrophic organisms, while the bottom waters were dominated by Arcobacter, with fewer numbers of the sulfate-reducting bacteria and the green sulfur bacteria Chlorobium. Sequences provisionally identified as anoxygenic purple and green sulfur bacterial clades dominated the photosynthetic communities in Inkwell’s bottom layer, reminiscent of bacterial populations found at greater depths in other stratified sinkholes. Results of this study suggest Inkwell presents an underrepresented ecosystem in current literature that might serve as a natural laboratory for research regarding competition between anoxygenic and oxygenic photosynthesic microorganisms and sulfur cycling dynamics.

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