Date Thesis Awarded

5-2011

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Kurt E. Williamson

Committee Member

Mark H. Forsyth

Committee Member

Randolph M. Chambers

Committee Member

Randolph A. Coleman

Abstract

Little is known about microbial dynamics in freshwater ecosystems, particularly compared to marine systems. The taxonomy of many freshwater bacterial lineages has been determined, but the drivers of community composition dynamics have yet to be clearly determined. Given that community composition determines which important processes occur and the rate at which they occur, an increased understanding of the drivers of community composition change is necessary. The purpose of this study was to and to track changes in the profile of the bacterial species in Lake Matoaka, an eutrophic, freshwater lake, in response to the primary seasonal, environmental and biological drivers. Surface water samples were collected monthly over an 18 month period, along with environmental data (temp, pH, nutrients (P and N), chl-a). Viral and bacterial abundances were determined using epifluorescence microscopy. DNA was extracted from bacterial cells captured on a 0.22 ?m filter and bacterial community profiles were generated using terminal restriction fragment length polymorphism (tRFLP). Profiles were compared by converting chromatograms to binary matrices based on the presences or absence of peaks. Pearson correlations and a BioEnv analysis were used to identify relationships between viral and bacterial abundance, viral and bacterial community composition and environmental factors. Bacterial communities were also characterized by sequencing of 16S rRNA clone libraries from two months, June 2009 and December 2009 (summer and winter), within the sample period. Distribution of T-RFs across the 18-month sampling period was analyzed by constructing cluster dendrograms, which suggested that there is no quantifiable seasonal/temporal trend in bacterial community composition. The only significant relationships revealed by correlation analysis were between bacterial and viral abundance, viral abundance and temperature, and bacterial abundance and temperature. BioEnv analysis indicated that the only environmental factor with any explanatory power in accounting for community composition change was temperature. However, inspection of dendrograms revealed that this relationship is not strictly linear and sample months do not cluster neatly based on temperature fluctuations. Moreover, viral and bacterial community compositions were determined to be very tightly linked by a Mantel test. 16S Clone libraries revealed that several dominant phyla were present within the lake, the foremost of these being Proteobacteria, consistent with the findings of previous freshwater studies. The distribution of genera varied between the two seasons. The bacterial assemblage of Lake Matoaka appears to be composed of a core of Proteobacteria that are consistently present, with a variable component that changes significantly over the annual cycle. While temperature was identified as having moderate explanatory power, a clear driver for community composition change was not determined. Future studies that include other biological and environmental factors, such as protozoan grazing and dissolved organic carbon. Future studies should also include a survey of the dynamics of community composition over several lakes of highly similar characteristics in order to clearly define drivers of bacterial community composition change in freshwater ecosystems.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

Comments

Thesis is part of Honors ETD pilot project, 2008-2013. Migrated from Dspace in 2016.

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