Date of Award


Degree Type


Degree Name

Master of Science (MS)




Microbial biofilms can be found on virtually all submerged surfaces in aquatic habitats, including rivers and streams. Biofilms are complex, taxonomically diverse communities of microorganisms (including algae and bacteria) that colonize solid surfaces and support a wide range of metabolic activities. Biofilms are critical components of river and stream ecosystems because they are key drivers of nutrient cycling processes (including nitrogen cycling) and because they serve as an important food source for higher trophic levels. Biofilms in urban streams are subject to a number of anthropogenic stressors, but research on the ecology of urban biofilms and their response to stressors has been limited. With the work from my thesis, I seek to improve our understanding of these important but understudied communities. My thesis project has two main components that will address two hypotheses related to biofilms in urban streams. Hypothesis 1 predicts that the type of algae present in a biofilm will influence both the taxonomic composition and activity of bacteria within the biofilm. Hypothesis 2 predicts that the taxonomic composition and activity of bacterial communities within urban streams will be affected by anthropogenic pollutants. Two main components will address these two hypotheses. Component 1 tests Hypothesis 1 through a laboratory experiment in which monocultures of four different algal species were grown in the laboratory with a mixed bacterial community collected from a field site. Next-generation sequencing of bacterial communities to assess the effects of algal species identity on the development of biofilm bacterial communities. Analysis of the sequence data shows that denitrifier community composition was significantly impacted by the identity of the algal species present. Component 2 of my project tests Hypothesis 2 with a field study in which I analyzed the composition and function of microbial communities collected from 3 stream sites in Baltimore, MD. These three sites are located along a previously studied urbanization gradient. I compared the microbial communities at these sites with concentrations of anthropogenic pollutants (pharmaceuticals and personal care products) to assess linkages between stressors and bacterial community responses. The results of this analysis suggests linkages exist between urbanization and the activity and composition of stream biofilm communities. Component 2 of my project will provide novel insight into the potential effects of anthropogenic pollutants on microbial communities within urban streams, and my project as a whole will add to our understanding of the factors that can influence microbial communities in urban habitats.

Creative Commons License

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

Available for download on Friday, July 25, 2025

Included in

Microbiology Commons