Digital Commons Network^™

Persistence Of Wastewater-Associated Antibiotic Resistant Bacteria In River Microcosms, Aoife P. Mahaney

Theses and Dissertations

The spread of antibiotic-resistant bacteria (ARB) associated with wastewater is a significant environmental concern, but little is known about the persistence and proliferation of these organisms in receiving water bodies after discharge. To address this knowledge gap, we performed a series of microcosm experiments in which river water was amended with either untreated or treated wastewater, and the abundance of viable ciprofloxacin-, Bactrim-, and erythromycin-resistant bacteria was monitored for 72 hours.

Both types of wastewater amendments increased the initial abundance of ARB compared to microcosms containing only river water. The increase was greatest with untreated wastewater, but that effect decreased …

Restricted Microbial Presence, Activity, And Community Structuring Within Dry Valley Soils Of Antarctica, Scott Fillerup George

Theses and Dissertations

The McMurdo Dry Valley region is the largest ice-free area of Antarctica. Harsh abiotic conditions of the polar desert ecosystem, including extreme cold, aridity, and limited nutrient availability select for unique taxa. The comparatively simple terrestrial ecosystem is well-suited for investigating edaphic influences on microbial presence, activity, and community structuring. The Dry Valleys are viewed as a useful analog for Mars astrobiology investigations. However, most biotic investigations have been focused on lower elevations, where an understanding of edaphic effects on microbial communities within its generally more favorable conditions has emerged. Transiently wetted Dry Valley water tracks may be analogous to …

Identifying Positive Selection In Multiple Subspecies Of Xylella Fastidiosa, Daniel Doroteo Flores

Theses and Dissertations

For this study, we will be looking to identify positive selection in eight genomes of the bacterial plant pathogen Xylella fastidiosa. A previous study used a branching method that identified 2 genes with positive selection along with a site-specific method identifying 34 genes showing positive selection. This current study focused specifically on the site-specific method, resulting in 28 genes (of 1,039 tested) showing positive selection. Of the 28 genes showing positive selection, 12 of them come from the pathogenicity, virulence and cellular structural categories. The remaining genes are found in the biosynthesis, metabolism, macro metabolism, and cellular process categories. …

Development, Validation, And Application Of A Novel Method To Separate And Quantify Silver Intracellular Uptake In Pseudomonas Aeruginosa, Mohammed A. Othman

Theses and Dissertations

Silver nanoparticles (AgNPs) have attracted tremendous attention as a potential broadspectrum antimicrobial agent to overcome multidrug resistant (MDR) infections. However, a comprehensive understanding to AgNPs bactericidal mechanism of action and the relative role of particulate versus ionic Ag in AgNPs antibacterial activity is lacking but essential for their optimization for potential medical applications. Therefore, a novel method to separate and quantify Ag internalization in P. aeruginosa was developed and validated through multimethod approach. The methods used were optical density at 600 nm (OD600), LIVE/DEAD staining, transmission electron microscopy (TEM), and sorbed Ag liberation assays. After optimizing the method, it was …

Characterization Of The Effects Of Heavy Charged Particle Exposure On The Radiation Resistant Bacterium Deinococcus Radiodurans, Todd A. Bryant

Theses and Dissertations

Although not an extremophile, Deinococcus radiodurans has proven to have exceptional resistance to ionizing radiation, specifically via gamma and X-ray photons. To date, no known experiments have bombarded the bacterium with charged particles larger than hydrogen. This study explored the effects on the organism’s ability to survive high linear energy transfer heavy-charged particle exposures of oxygen ions. It also investigated the effects of low linear energy transfer ultraviolet radiation on various mutants. Two uvrB mutants were created to ascertain the importance of the gene in single-strand break repair following gamma irradiation and two recF mutants were created to explore the …

Characterization Of Silicon Ion Exposure On Deinococcus Radiodurans, Richard F. Daughtry

Theses and Dissertations

Deinococcus radiodurans is a robust bacterium that is known for its extraordinary resistance to ionizing radiation. In general, many of the investigations of this bacterium's resistance have revolved around low linear energy transfer radiation, such as gamma and electron radiation. This study explored Deinococcus radiodurans's ability to survive high linear energy transfer radiation, specifically proton and neutron radiation. Deinococcus radiodurans was dehydrated to reduce the effects of low linear energy transfer radiation. The bacteria were exposed to both neutron and proton radiation of varying amounts and rehydrated. The resulting colonies were counted and compared to colonies of non-irradiated control samples …

The Loss Of Methanol Utilization In Methylobacteria, Justin T. Skariah

Theses and Dissertations

Methylobacteria primary uses Cl substrates as a carbon and energy source. This experiment was performed to see if Methylobacteria would lose the ability to use Cl compound methanol after prolonged exposure to multi-carbon substrates. To determine this, the bacteria was grown on MR2A3 (multi-carbon substrates) and MOM (single-carbon substrates) for multiple generations and tested for loss of function on a series of generations. These tests include streaking plates of MOM and R2A with bacteria from MR2A3 then getting a bacterial colony count and also toothpick transfers of the colonies to verify findings. After 20 generations there were no significant decrease …

Image-Charge Detection €“ Novel Instrumentation And Applications, Brandon Lee Barney

Theses and Dissertations

Image-charge detection is an analytical technique in which a highly-charged particle is detected by the magnitude of the image current that it generates in a detecting electrode. This current is represented as a voltage between the charged particle and the sensing electrode. It is a single particle detection method, ideal for the analysis of large, variable mass particles such as biological cells. Some of the physical properties of Bacillus subtilis spores were explored using different applications of image-charge detection. B. subtilis is a gram-negative spore-forming bacteria that has been shown to exhibit extremophile behavior. The particular extremophile behavior that was …

High Salinity Stabilizes Bacterial Community Composition And Activity Through Time, Tylan Wayne Magnusson

Theses and Dissertations

Dormancy is a plausible strategy for bacteria to overcome the effects of temporal fluctuations in resources or stresses and await more “optimal” conditions to resume metabolic activity and growth. Seasonal changes in environmental conditions force microbes to adjust their metabolic activity accordingly, and community composition drastically shifts. In extreme environments, however, the overriding effects of a constant stress may constrain the need or benefit of bacteria entering dormancy. In hypersaline lakes, high metabolic activity is required to maintain adaptations that permit survival. Sampling from six lakes on a salinity gradient (0.05% – 30.3%), we measured seasonal fluctuations in bacterial dormancy …

Integrated Nanoscale Imaging And Spatial Recognition Of Biomolecules On Surfaces, Congzhou Wang

Theses and Dissertations

Biomolecules on cell surfaces play critical roles in diverse biological and physiological processes. However, conventional bulk scale techniques are unable to clarify the density and distribution of specific biomolecules in situ on single, living cell surfaces at the micro or nanoscale. In this work, a single cell analysis technique based on Atomic Force Microscopy (AFM) is developed to spatially identify biomolecules and characterize nanomechanical properties on single cell surfaces. The unique advantage of these AFM-based techniques lies in the ability to operate in situ (in a non-destructive fashion) and in real time, under physiological conditions or controlled micro-environments.

First, AFM-based …

A Mathematical Model Of Moisture Movement And Bacterial Growth In Two-Dimensional Porous Medium, Rachel Elizabeth Tewinkel

Theses and Dissertations

Bacterial growth in sand is of concern in regard to the health of beaches. A mathematical model is presented that represents the movement of moisture and the growth of bacteria through a beach. Simulations were run by numerically solving Richards Equation using a Finite Volume Method in order to track moisture movement. A model of moisture-dependent bacterial growth was then implemented. These simulations show that elevated bacteria counts following rain events do not necessarily result from bacteria in the body of water, but can also be sourced from the sand. Additionally, four different moisture-dependent bacterial growth models are compared to …

Environmental Regulation Of Tidal Wetland Microbial Communities And Associated Biogeochemistry, Ember Morrissey

Theses and Dissertations

Microbial communities play an essential role in carrying out the biogeochemical cycles that sustain life on Earth, yet we know very little about their ecology. One question of particular interest is how environmental conditions shape microbial community structure (i.e., the types of organisms found in the community and their relative abundance), and whether such changes in structure are related to biogeochemical function. It is the aim of this dissertation to address this question via the examination of carbon (C) and nitrogen (N) cycling in wetland ecosystems, which due to their diverse hydrology have a profound influence on biogeochemical cycles. With …

Resource Legacies And Priming Regulate Microbial Communities In Antarctica's Dry Valleys, Sabrina Deni Saurey

Theses and Dissertations

Multiple mechanisms control bacterial community structure but two in particular, the "legacy" of past environmental conditions, and the "priming" of bacteria to respond to seasonal or reoccurring fluctuations in resources, have the potential to determine both bacterial communities, as well as, temporal shifts in active bacterial taxa. To begin to evaluate the legacy effects of resources on microbial communities, we added four limiting resources annually (i.e., water only; C-mannitol + water; N-NH4NO3 + water; and C, N + water) and measured shifts in bacterial community composition after seven years in a cold desert ecosystem in the McMurdo Dry Valleys, Antarctica. …

Hypersaline Lake Environments Exhibit Reduced Microbial Dormancy, Joshua Christopher Vert

Theses and Dissertations

From acid seeps and deep-sea thermal vents to glacial ice and hypersaline lakes, extreme environments contain relatively simplified communities consisting of extremophiles that have evolved to survive and thrive under adverse abiotic conditions. In more neutral environments, microorganisms use dormancy as a common life history strategy to weather temporal fluctuations of resources or stresses until more 'optimal' conditions are present. It is unclear if dormancy is an essential survival mechanism for microorganisms in extreme environments; however, recent studies suggest that extreme environments may create stable conditions for extremophiles to the extent that dormancy is of less ecological importance. Using lake …

Estimation Of Aerosolized Antibiotic Resistant Bacteria Concentrations From Wastewater Treatment Facilities Using Spatially-Based Dispersion Modeling, Renee Nichole Dickman

Theses and Dissertations

Pathogenic bacteria can develop resistance to antibiotics to which they were previously sensitive, resulting in increased morbidity and mortality worldwide [1]. The increase in drug resistance in bacteria is an emerging public health concern. The activated sludge tanks of wastewater treatment plants are known sources of antibiotic resistant bacteria. These resistant bacteria can become aerosolized and disperse downwind. Using previously sampled aerosol concentrations and meteorological data, a Gaussian dispersion model was developed to estimate the concentration downwind from a selected wastewater treatment facility. The emission rate was calculated to be 7,941 CFU/m²/sec ± 2,149 CFU/m²/sec. This value was used in …

Ocean Acidification: Understanding The Coastal Carbon Pump In A High Co2 World, Rachel Cooper

Theses and Dissertations

Since the 1800s, carbon dioxide emissions due to human activities have contributed significantly to the amount of carbon in the atmosphere. Approximately a third of this carbon is absorbed by the ocean, through air-sea fluxes at the ocean surface (Sabine, 2004). Increased CO2 has changed the carbon chemistry of the ocean and hence the pH. pH is expected to drop by 0.4 by the year 2100. It is unclear how this lower pH will affect carbon cycling and sequestration with respect to the biological carbon pump. Most studies have focused on open ocean phytoplankton or bacterial communities in large, stationary …

Depth And Time Related Variations Of Microbial Communiites In An Emergent Freshwater Wetland, Amy Jenkins

Theses and Dissertations

Soils, and the microbial communities contained within them, are vital for most chemical, physical, and biological processes. This study investigated how microbial community structure responded to environmental changes, such as hydrology, across vertical space (depth) and time in an emergent fresh water wetland. Research was conducted in a non-tidal freshwater wetland along the James River (Charles City County, Virginia) by establishing plots in two areas that experienced different hydrologic regimes and plant communities. Soil cores (30 cm) were collected monthly from January 2008 to February 2009, and then every two to three months thereafter until October 2009, for a total …

Factors Influencing The Abundance, Community Composition And Activity States Of Bacterioplankton From The Tidal Freshwater James River, Catherine Luria

Theses and Dissertations

Aquatic bacteria respond to changing environmental conditions through a variety of mechanisms including changes in abundance, shifts in community composition and variable activity states. In the tidal-freshwater James River, variation in bacterial abundance was linked to nutrient availability and autochthonous production with highest bacterial densities associated with low-nutrient, high-chlorophyll a conditions. Laboratory experiments revealed that bacterial growth rates were nutrient limited at the low-nutrient site, while co-limitation (nutrients, glucose, light) was apparent at the high nutrient site. Despite large differences in abundance, community composition was similar based on TRFLP and 16S rDNA pyrosequencing. Community similarity was lower among rRNA libraries …

The Response Of Hn4 Cells To Porphyromonas Gingivalis Dna, Cheyanne Warren

Theses and Dissertations

Periodontal disease is one of the most common human diseases. Bacteria trigger the onset and progression of the disease and among them Porphyromonas gingivalis has been demonstrated to be a major etiologic agent. Although the interaction of the bacterium with the host is of major importance for the understanding of the disease mechanisms, both the host as well as the pathogen components involved in the interaction remain poorly understood. One of the bacterial components capable of eliciting a host response is unmethylated CpG DNA motifs found in bacteria. Thus, the first aim was to determine the response of oral epithelial …

Heavy Metal Toxicity In Bioremediation: Microbial Cultures And Microscopy, Jason B. Goodbody

Theses and Dissertations

This research employed a variety of microscopy and spread plating techniques to observe the effects of heavy metal treatments on a toluene-selected bacterial population. Microbial colonies were cultured on spread plates and the resulting numbers were compared to respiration data. The mechanisms of reproduction were demonstrated to be more sensitive to metal treatments than were the mechanisms of respiration. Phase contrast, Gram stain, fluorescent microscopy, were used to compare and document a wide variety of bacteria resulting from different metal treatments as well as from environmental changes within the source bioreactor. The removal of sensitive bacteria and the selection of …

Folate Content Of Bacillus Subtilis, David Nelson Hintze

Theses and Dissertations

Bacillus subtilis can synthesize deoxythymidylate via either of two pathways. The working hypothesis is that the two reactions are very similar, differing only with respect to specificity for the type of folate required as substrate. The folates from B. subtilis were isolated and were determined by gel chromatography to be derivatives of pteroyltriglutamate and pteroyldiglutamate. Kav values for the two folate species are reported. Conjugase treatment revealed no other highly conjugated folates present. It was also observed that mutants deficient in one or the other of the two pathways grow at the same rate as wild-type cells under conditions allowing …

Oxidation Of Molybdenite With The Aid Of Microorganisms, Ralph Anderson

Theses and Dissertations

This work represents a study on the biological oxidation of molybdenite, MoS2. The principal objective of this study was to investigate the possibility of the biological oxidation of molybdenite, to determine the physical and chemical conditions under which the oxidative process occurs, and to develop a strain of bacteria or alter the activity of the microorganisms by acclimatization to increase their activity on sulfide minerals, in particular molybdenite. Minerals used in this study were pyrite (FeS2), chalcopyrite (CuFeS2), molybdenite concentrate, and molybdenite ore. The microorganisms used in this investigation were autotrophic bacteria obtained from the leaching streams of Bingham Canyon, …