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Title:Investigating the effect of phytoplankton on bacterial community composition across different environmental contexts
Author(s):Paver, Sara
Director of Research:Kent, Angela D.
Doctoral Committee Chair(s):Kent, Angela D.
Doctoral Committee Member(s):Cáceres, Carla E.; Metcalf, William W.; Whitaker, Rachel J.
Department / Program:School of Integrative Biology
Discipline:Ecology, Evolution, and Conservation Biology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):community ecology
microbial ecology
species interactions
algal-bacterial interactions
context dependence
Abstract:The following dissertation encompasses a series of investigations aimed at testing the hypothesis that phytoplankton seasonal succession effects changes in bacterial community composition and characterizing interactions between phytoplankton and bacteria across different environmental contexts. Observational and experimental approaches were combined to determine the effect of phytoplankton on the composition of the bacterial community in three humic lakes in Northern Wisconsin where correlated patterns of community change between phytoplankton and bacteria have previously been observed. Because community-level analyses can aggregate ecologically distinct bacterial populations into a single operational taxonomic unit, the effect of phytoplankton on the composition of subtypes within the cosmopolitan freshwater bacterial genus Polynucleobacter was additionally determined. Changes in the abundance of phytoplankton populations explained a substantial amount of temporal variation in Polynucleobacter composition, similar to variation in total bacterial community composition explained by phytoplankton. Full factorial algal exchange experiments combining bacteria from each lake with phytoplankton from one of the lakes or a no-phytoplankton control confirmed the effect of phytoplankton presence and composition on the composition of the bacterial community and Polynucleobacter subtypes. Bacterial community response appeared to be primarily due to phytoplankton enriching for specific free-living bacteria. However, phytoplankton-associated bacteria and Polynucleobacter subtypes did contribute to observed differences between phytoplankton treatments and corresponding no-phytoplankton controls. Light and temperature vary temporally and with depth in lakes and have the potential to modify interactions with phytoplankton as well as influence bacteria directly. To determine how phytoplankton, light, and temperature combine to affect bacterial communities, a multi-factorial experiment was conducted. Bacteria from two of the humic lakes were combined with phytoplankton assemblages from each lake (“home” or “away”) or a no-phytoplankton control and incubated for 5 days under all combinations of light (surface, ~25% surface irradiance) and temperature (5 levels from 10°C to 25°C). Light had a direct effect on bacterial community composition, potentially due to stimulating the growth of phototrophic bacteria. Temperature effects were largely phytoplankton-mediated and the effect of temperature was greatest for “away” phytoplankton treatments. We hypothesize that the enhanced effect of “away” phytoplankton on bacteria is due to the availability of a different pool of exudates than bacteria had become acclimated to in their “home” lake. To determine support for phytoplankton exudates to affect bacterial succession, the glcD gene, which indicates genetic potential for bacteria to use the algal exudate glycolate, was characterized in Emerald Lake, an oligotrophic high-elevation lake that shifts from primarily terrestrial-derived organic matter following ice-off to primarily phytoplankton-derived organic matter. glcD genes were not detected in early season samples when phytoplankton-derived resources were scarce. Following this period, glcD gene composition exhibited significant changes through time, providing support for exudate-mediated phytoplankton effects and strengthening the evidence for shifts in dissolved organic matter to structure bacterial communities. Results from these studies contribute to the ability to predict changes in bacterial community composition and determine underlying processes, thereby providing a backdrop for examining mechanisms that create and maintain diversity and enhancing the ability to forecast community responses to environmental change.
Issue Date:2014-01-16
Rights Information:Copyright 2013 Sara Paver
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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