Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item MICROBIAL BIOFILMS ON MICROPLASTICS: A LOOK INTO THE ESTUARINE PLASTISPHERE OF THE CHESAPEAKE BAY(2021) Sosa , Ana Paula; Chen, Feng; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microplastics are plastic particles that are smaller than 5 millimeters and are often found as pollution in our waterways. These polymer particles are globally distributed and are a direct result of human activity. Because of their rigidity and durability, microplastics are an ideal substrate for enhanced microbial growth and biofilm development. While microplastics have been studied in various contexts, only few studies have characterized the microbial communities on different types of plastic particles, but no study has been done in the estuarine water. In this study, we exposed three different types of plastics (polypropylene, polystyrene, and polylactic acid) to the water of Baltimore’s Inner Harbor, along with a non-plastic glass control. We used both in situ and in vitro incubations to understand the development of biofilm communities on microplastics. Microbial communities were analyzed based on the 16S rRNA gene sequences. We found that microbial composition on biofilm is distinct from that in the surrounding water, and different microplastic types have a minor impact on the composition of biofilm communities. The similarity between microbial communities on plastic and non-plastic particles suggests that surface supports rather than material types could be more critical for biofilm formation. Succession of microbial communities on the microplastics and interesting bacterial groups were described. Isolation and microscopic observations were also applied in this study. The presence of phototrophic organisms like filamentous cyanobacteria and Auxenochlorella on microplastic biofilms is interesting, and little is known about their contribution to carbon fixation in the ocean. Biofilms formed on microplastic surfaces could potentially affect the ecosystems via different mechanisms, including local nutrient cycling and the transportation of invasive or harmful species. As plastic production and mismanagement continues to be pervasive in our society, it is paramount that we include biofilm development into the framework of general ecology in order to truly understand the impact of plastic pollution and safeguard our ecosystems.Item ASSESSING THE IMPACTS OF NON-POINT SOURCE FRESHWATER AND NUTRIENT INPUTS ON A SHALLOW COASTAL ESTUARY(2019) Butler, Thomas; Hood, Raleigh R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Academic research models for Chesapeake Bay have, traditionally, been forced with USGS inputs, flows and nutrient loads from 10 major rivers. These tributaries fail to account for 100% of the inputs entering the Bay. In contrast, models used for determining Total Maximum Daily Load for Chesapeake Bay are forced with output from a watershed model at thousands of locations, presumably, accounting for all these inputs. Our aim is to increase understanding of the impacts different forcing schemes have on water quality model simulation. Simulations were completed using three forcing approaches: 1) using “traditional” USGS-derived input from 10 major rivers; 2) using “concentrated” input from 10 major rivers derived from watershed model output; and 3) using “diffuse” input from 1117 rivers derived from watershed model output. Comparisons of these schemes revealed large impacts on simulations in Chesapeake Bay during periods of high flow and extreme weather events under diffuse forcing.Item Adaptive Mechanisms of an Estuarine Synechococcus based on Genomics, Transcriptomics, and Proteomics(2016) Marsan, David Wilfred; Chen, Feng; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Picocyanobacteria are important phytoplankton and primary producers in the ocean. Although extensive work has been conducted for picocyanobacteria (i.e. Synechococcus and Prochlorococcus) in coastal and oceanic waters, little is known about those found in estuaries like the Chesapeake Bay. Synechococcus CB0101, an estuarine isolate, is more tolerant to shifts in temperature, salinity, and metal toxicity than coastal and oceanic Synechococcus strains, WH7803 and WH7805. Further, CB0101 has a greater sensitivity to high light intensity, likely due to its adaptation to low light environments. A complete and annotated genome sequence of CB0101 was completed to explore its genetic capacity and to serve as a basis for further molecular analysis. Comparative genomics between CB0101, WH7803, and WH7805 show that CB0101 contains more genes involved in regulation, sensing, and stress response. At the transcript and protein level, CB0101 regulates its metabolic pathways, transport systems, and sensing mechanisms when nitrate and phosphate are limited. Zinc toxicity led to oxidative stress and a global down regulation of photosystems and the translation machinery. From the stress response studies seven chromosomal toxin-antitoxin (TA) genes, were identified in CB0101, which led to the discovery of TA genes in several marine Synechococcus strains. The activation of the relB2/relE1 TA system allows CB0101 to arrest its growth under stressful conditions, but the growth arrest is reversible, once the stressful environment dissipates. The genome of CB0101 contains a relatively large number of genomic island (GI) genes compared to known marine Synechococcus genomes. Interestingly, a massive shutdown (255 out of 343) of GI genes occurred after CB0101 was infected by a lytic phage. On the other hand, phage-encoded host-like proteins (hli, psbA, ThyX) were highly expressed upon phage infection. This research provides new evidence that estuarine Synechococcus like CB0101 have inherited unique genetic machinery, which allows them to be versatile in the estuarine environment.Item The effects of oxygen transition on community metabolism and nutrient cycling in a seasonally stratified anoxic estuary(2014) Lee, Dong-Yoon; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gradients of dissolved oxygen concentrations in seasonally stratified estuarine water columns directly influence microbial composition and metabolic pathways, resulting in annually recurring spatiotemporal chemical gradients of redox-active species. Understanding such microbial responses to variable geochemical conditions and elucidating the diversity of microbial processes are needed to comprehensively identify ecosystem functions. At first this study describes an investigation of the relationships between microbial processes and geochemical conditions. To assess the contribution of different biological redox processes on carbon and nitrogen cycles in the Chesapeake Bay, we used observational and experimental approaches as well as utilization of monitoring datasets to facilitate an assessment of ecosystem-level metabolism. Observations revealed a general positive association of community metabolism with strong gradients of redox-related variables and hydrodynamic characteristics, although geochemical and environmental conditions varied seasonally across oxic transitions and interannually across degrees of stratification. The most distinct evidence supporting the positive association were vertical distributions of community respiration with the highest average rates in the most stratified regions coincident with the depths of the steepest gradient of chemical compounds. Although organic matter availability may be enhanced due to hydrodynamically induced stability, our investigation of factors driving the pattern revealed that differential responses and metabolic strategies of microbial communities result in high respiration near oxyclines. Investigation of vertical profiles of redox-related variables also revealed that the coexistence of oxidants and reduced compounds further provides an optimal condition for other electron accepting processes, including chemoautotrophy and anoxygenic photoautotrophy. The strong interdependence between environmental conditions and variability in microbial metabolism also reflected in patterns of plankton assemblages. An ammonium mass-balance analysis revealed that increases in vertical ammonium dispersion during severe hypoxia cause a shift of plankton assemblages towards heterotrophy, subsequently supporting a deep secondary microbial food web in the vicinity of oxic/anoxic interface. Overall, results from this research indicate that the estimation of more accurate net ecosystem metabolism should take into consideration of the highly variable nature of community metabolism associated with both geochemical gradients and stratification.