Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

M.S. in Biological Science



First Advisor

Colin R. Jackson

Second Advisor

Stephen J. Brewer

Third Advisor

Clifford A. Ochs

Relational Format



Spatial variation in the structure and function of bacterial communities is far more complex than previously believed. High throughput sequencing techniques have begun to elucidate the dynamic worldwide patterns of bacterial biogeography; however, there are still many ecosystems for which there is little to no representative data. Currently there are no high throughput-based analyses of bacterial assemblages in large rivers. Rivers form important connections between terrestrial land use and marine biogeochemistry and act as conduits for organisms and allochthonous nutrients. Bacteria dominate carbon cycling and nutrient processing in rivers, and therefore can influence regional and global elemental cycles. This study characterized the structure of bacterial assemblages of the major tributaries to the lower Mississippi River using high throughput ion torrent pgm sequencing of the 16s rrna gene, and the function of these communities using assays of extracellular enzyme activity. A total of 715,120 valid bacterial 16s rrna sequences were classified into 30,211 operational taxonomic units (otus), although many of these otus were of very low proportional abundance. The most abundant individual otu was identified as being related to the dominant marine alphaproteobacteria pelagibacter/sar11 and was found in all rivers. The most abundant bacterial phylum was the cyanobacteria, of which a number of genetically distinct otus were identified as being similar to prochlorococcus. Community structure was related to river physiochemistry, although there was no consistent physicochemical factor responsible for these differences. While there were different bacterial communities in each river, the greatest difference in assemblage structure was between free living cells and those associated with particles. Despite having different environmental characteristics and distinct bacterioplankton communities, there were no consistent differences in enzyme activity between rivers, although aspects of community structure could be linked to extracellular enzyme activity. Overall, this research shows that large rivers of the Mississippi River basin harbor distinct bacterioplankton communities but also suggests that these structurally different bacterial assemblages may show similar ecological functions related to nutrient acquisition and organic carbon mineralization.

Included in

Microbiology Commons



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