Microbiology Commons^™

Exploring Competitive Dynamics Between Pseudomonas Baetica And Salmonella In A Polymicrobial System, Braxton E.M. Stout

Electronic Theses and Dissertations

The global rise in antimicrobial resistance has catalyzed a greater focus on polymicrobial research aimed at characterizing microbial interactions and uncovering new therapeutic strategies. Though it has long been of interest, environmental soil-derived bacteria remain largely under-represented in research and thus uncharacterized in this field. This project aimed to identify soil microbes that display inhibitory mechanisms to potential nosocomial pathogens. Soil sample S1S3-2 displayed inhibitory phenotypes toward numerous bacteria and was identified as Pseudomonas baetica. In both planktonic and biofilm growth, P. baetica was able to inhibit Salmonella arizonae through a contact-dependent and temperature-dependent manner. Screening of a transposon insertion …

Escherichia Coli Concentrations In Sand And Water At Tributary-Influenced Lake Michigan Beaches, Josie Elaine Kuhlman

Masters Theses

Contamination of public recreational water and sand is a human health concern, creating a management challenge for public health officials. Past research has shown that Escherichia coli can persist in sediment and can be washed into recreational water. Currently, beach monitoring practices only utilize E. coli concentrations in water samples to determine beach safety and do not consider potential exposure to sediment/sand concentrations. In this study, I investigated the relationship between E. coli concentrations in water and sand samples, which will aid public health officials in making more informed decisions about beach closures. I utilized culture-based measurements of E. coli …

Function And Regulation Of Long Polar Fimbriae During Enterohemorrhagic Escherichia Coli Infection, Walter J. Galdamez

Dissertations and Theses (Open Access)

Enterohemorrhagic Escherichia coli (EHEC) is a foodborne pathogen that causes severe gastrointestinal disease and hemolytic uremic syndrome. EHEC employs multiple virulence factors to colonize the host intestine, including the locus of enterocyte effacement (LEE) encoded type III secretion system, intimin, and flagella, yet the role of long polar fimbriae (Lpf) in adhesions and infection remains less well understood. Long polar fimbriae can mediate bacterial attachment to host cells in vitro, yet the regulation and function of its two fimbrial operons, lpf1 and lpf2 in vivo remain poorly understood. Preliminary RNA-seq data from zebrafish infected with EHEC reveal that expression of …

Defining The Role Of Spxa1 And Spxa2 In Group A Streptococcus (Gas), Gretchen Anne Morrison

Dissertations and Theses (Open Access)

Group A Streptococcus (GAS) is a human-restricted pathogen whose global incidence has surged in the post-COVID era. The ability of GAS to shift from a colonizing to invasive phenotype depends on coordinated virulence gene regulation in response to host-imposed stressors. The paralogous global transcriptional regulators, SpxA1 and SpxA2, have emerged as central mediators of these adaptive responses; however, the mechanisms by which these regulators influence both global gene regulation in direct response to external stresses and the host response as a result of regulatory changes remain incompletely understood. Using an integrated multi-omic approach, we define the distinct yet interconnected regulatory …

Mutational Analysis Of Domain Functions In The Yeast Decapping Enzyme Dcp2, Jellisa Ewan, Ambro Van Hoof

Dissertations and Theses (Open Access)

In yeast, the major mRNA decay pathway involves deadenylation of the 3’ poly-A tail, followed by decapping of the 5’ m7Gppp cap and subsequent 5’ to 3’ degradation or 3’ to 5’ degradation. This is carried out by Pan2/Pan3 and Ccr4/Not deadenylases, the decapping enzyme Dcp2, and Xrn1 and  RNA exosome exoribonucleases, respectively. The eukaryotic mRNA decapping enzyme complex, Dcp1/Dcp2, is essential in yeast, and deletion of either gene is lethal. However, the deadenylases that act upstream and the 5’ exoribonuclease that act downstream of the decapping step are not, even though they are all highly conserved with no known …

Describing Propagation Of Carbapenem-Resistant Acinetobacter Baumannii Through Comparative Genomics And Phenotypic Analysis Of Modern-Day Clinical Isolates, Emma Graffice

ETDs from 2020-2029

Understanding the genomic structure of bacterial populations is essential for tracking antimicrobial resistance and informing public health strategies to prevent spread of multidrug resistant organisms. In this study, we investigated the diversity and distribution of carbapenem-resistant Acinetobacter baumannii (CRAb) lineages across a major healthcare system in the U.S. Deep South through both retrospective and prospective isolate collection. Our analysis revealed a heterogeneous population composed of multiple genotypically and phenotypically distinct lineages. To improve the resolution of lineage classification, we applied average nucleotide identity (ANI) as a high-resolution metric for comparative genomics. A ≥99% ANI threshold effectively delineated lineages, outperforming traditional …

Jnk Signaling Impacts Car-T Cell Effector Function, Charles Kuhlmann

ETDs from 2020-2029

The potent cytotoxic activity of T cells serves as a natural defense against cancers. Chimeric antigen receptor (CAR) T cell therapy represents a strategy for harnessing T cells against advanced tumors. CAR-T cell therapy has seen striking success against hematologic malignancies, prompting its application to new diseases. Ovarian cancer is a highly lethal disease characterized by frequent recurrence and aggressive nature, prompting the investigation of CAR-T cell therapy as a salvage regimen. However, like in other solid tumors, the early performance of CAR-T cell therapy in ovarian cancer is poor. While many strategies exist for improving the longevity of CAR-T …

Discovery Of Bmi-Associated Gut Microbiome Signatures In The Awi-Gen 2 Cohort, Meriem Yagoubi

Theses and Dissertations

Obesity is increasing across sub-Saharan Africa amid rapid dietary, environmental, and urbanization transitions, yet the gut microbiome features associated with adiposity in African populations remain under-characterized. This study investigated whether species-level gut microbiome composition is associated with body mass index (BMI) in the AWI-Gen 2 cohort, and whether BMI-associated microbial signals remain detectable after accounting for the dominant geographic structure of the microbiome. Gut microbiome community structure and diversity were characterized across 1,665 participants, and differential abundance analysis was used to identify taxa associated with BMI after controlling for study site. Machine learning models were then trained to assess how …

Microbial Literacy, Equity, And Sustainability At Cal Poly: A Policy Framework With University Housing As A Pilot Case, Joseph B. Fewel

Biological Sciences

Microorganisms play a fundamental role in human health, environmental systems, and the functioning of built environments, yet they remain largely absent from sustainability and public policy discussions. This project proposes a framework for integrating microbial literacy, equity, and health into institutional decision-making, using California Polytechnic State University (Cal Poly) as a case study and university housing as a pilot site for implementation. Drawing on interdisciplinary literature in microbiology, public health, environmental justice, and sustainability, as well as policy analysis and stakeholder interviews, this project examines how campus systems, including housing, ventilation, sanitation, food systems, and waste management, shape microbial exposure …

Marine Heatwaves And Fish Reproduction: Endocrine Responses In The Eurythermal Sheepshead Minnow (Cyprinodon Variegatus), Isabel Villafuerte

Master's Theses

Marine heatwaves associated with climate change are increasing in frequency and severity, posing significant threats to fish populations in shallow habitats such as estuaries and salt marshes. Because temperature is a primary regulator of fish reproduction, understanding how heatwaves affect reproductive physiology is critical for anticipating the biological consequences of ongoing climate change for coastal fishes. Here we examined how simulated heatwave conditions affect the reproductive hypothalamic-pituitary-gonadal (HPG) endocrine axis in the estuarine sheepshead minnow (Cyprinodon variegatus), a eurythermal fish well suited to studying thermal stress responses in estuarine environments. Adult sheepshead minnows acclimated to a daily oscillating …

Immunomodulatory And Signaling Molecules From Plant-Associated Bacteria: Toll-Like Receptor 4 Agonist Adjuvants And Diketopiperazine-Mediated Communication, Marian Romaine

Dissertations, Theses, and Capstone Projects

Medicinal plants and their associated microbiomes constitute a rich source of bioactive natural products with applications in immunotherapy and microbial ecology. Herbal formulations have long been valued for safe immune enhancement, while bacterial signaling molecules govern community behaviors critical to pathogenesis, symbiosis, and environmental processes. Bacterial lipopolysaccharides (LPS) from plant-associated Gram-negative bacteria have emerged as potent TLR4 agonists, yet their endotoxic potential limits direct use, and diketopiperazines (DKPs) serve as versatile quorum-sensing mediators capable of modulating biofilms in mixed microbial systems.

The work in this thesis comprises two independent but complementary research strands. The first strand pursued the engineering of …

Protein Glycosylation In Natural And Synthetic Minimal Genome Mycoplasmas, John Sanford

ETDs from 2020-2029

Mycoplasmas are cell wall-less bacterial symbionts with remarkably streamlined genomes. Mycoplasmas offer two intriguing model organisms for studying concepts of minimal life. Mycoplasma genitalium has streamlined its genome to 580-kbp while maintaining virulence to suit its niche of parasitizing the human urogenital tract. The J. Craig Venter Institute has synthesized and transplanted a 543-kbp genome into a recipient cell, resulting in a non-pathogenic organism termed JCVI-syn3A. The conservation of a biological process in M. genitalium and JCVI-syn3A strongly implies an essential function in mycoplasmas, and potentially all life. Despite common thought of mycoplasmas being the simplest cells, much of their …

Exploring The Durability Of Marine Picocyanobacterial Microcolonies, Erik Swanson

University Honors Theses

Picocyanobacteria of the genus Synechococcus are widespread aquatic photoautotrophs that play essential roles in primary production and carbon cycling. Some Synechococcus strains form multicellular microcolonies, but the mechanisms of cell-to-cell attachments and structural durability of these microcolonies remain poorly understood. This research investigated the physical durability of microcolonies in two marine Synechococcus strains (CC9605 and CC9311) using physical disruption treatments. Cultures were subjected to vortexing and sonication treatments, and populations of single cells and microcolonies were quantified using flow cytometry based on differences in measures of size. Results indicated that strain CC9605 showed no significant treatment effect, whereas CC9311 displayed …

Developing A High-Resolution Off-Axis Common-Mode Digital Holographic Microscope, Lucy Cook

University Honors Theses

Off-axis digital holographic microscopy (DHM) is a powerful tool for 3D, non-invasive live-cell tracking without moving parts. However, traditional setups face an inherent dilemma: split-path interferometers offer high spatial resolution but poor temporal stability, while more stable common-mode configurations are historically limited to lower numerical aperture (NA) regimes. This thesis bridges that gap by scaling a common-mode DHM architecture into a high-resolution benchtop instrument featuring NA = 0.65 objectives, paired with a high-power 520 nm laser source to combat transmission losses and sustain imaging frame rates across an expanded optical footprint. We map the multi-variable design space required to satisfy …

Evaluating Soil Health And Crop Yield In Louisiana Agricultural Systems: Impacts Of Best Management Practices And Prediction Models, Hector J. Mendoza Lagos

LSU Doctoral Dissertations

The adoption of conservation management practices is critical for improving soil health, enhancing nutrient use efficiency, and sustaining crop productivity in row crop systems in Louisiana. This study evaluated the role of conservation agronomic practices, soil biochemical indicators, and machine learning predictive models to improve soil nutrient dynamics, soil health indicators, microbial communities (MC), and crop productivity on a corn (Zea mays L.) research plot scale and in a commercial forty-hectare cotton (Gassypium hirsutum L.)-corn-soybean (Glycine max L.) rotation system in northeast Louisiana. The objectives of the study were to evaluate soil nutrient dynamics and MCs under …

Examining The Ligands, Location, And Function Of Toll-Like Receptor 10, Kiefer Keanu Tam

Master's Theses

Toll-like receptors are a class of innate immune pattern recognition receptors that detect pathogen-associated molecular patterns and regulate downstream inflammatory responses. Toll-like receptor 10 remains the only human TLR whose ligand specificity, cellular localization, and immunological function are not fully defined. Emerging evidence suggests that TLR10 may play an anti-inflammatory role and can heterodimerize with TLR2 to modulate immune signaling. Previous studies from our laboratory demonstrated that stimulation with heat-killed Mycobacterium tuberculosis promotes TLR2-TLR10 heterodimerization and trafficking to the cell surface. In this study, we expanded our ligand panel to include additional gram-positive bacteria, particularly anti-inflammatory probiotic species, to further …

Characterizing The Microbial Structure And Function In Black Soldier Fly Digested Dairy Manure And Subsequent Larvae, Branden N. Pierce

Theses and Dissertations

This work examined the microbial structure and gene expression found in Black Soldier Fly larval guts and their frass when reared on dairy cattle manure that had been amended with either R. rhodococcus 21198, P. polymyxa 8158, or both and compare the results to larvae reared on untreated manure. First an overview of literature surrounding projected global food supplies and the possible use of insects to either increase them or mitigate the environmental effect of producing said supply. A cellulose degradation assay was performed to assist in determining which bacterial species to use as amendments. Characterization of the microbial communities …

Skin Of Frog And Scale Of Dragon: Nutritional Cues, Life Cycle Kinetics, And Secretome Dynamics In Batrachochytrium Dendrobatidis, Naomi C. Okada

UNLV Theses, Dissertations, Professional Papers, and Capstones

Nearly 50% of amphibian species are at risk of extinction, making them the most threatened group of vertebrates on the planet. A major driver of these declines is the pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd), which causes the fatal skin disease chytridiomycosis. Since its discovery in the late 1990s, Bd has been directly implicated in the extinction of 90 species of amphibians and the declines of hundreds more. Despite this devastating ecological impact, relatively little is known about its basic cellular biology.

Bd has a multi-stage asexual life cycle consisting of a motile and infectious zoospore, which encysts (into a …

Impacts Of Salinity On Microbial Enzyme Activity In Coastal Waters, Natali Ariyoshi

Honors Theses

Microbial extracellular enzymes are critical for the breakdown of organic matter and nutrient cycling in aquatic ecosystems. Extracellular enzyme activity serves as an indicator of nutrient turnover rates, metabolic states, and nutrient limitations within an ecosystem. Coastal ecosystems are especially dynamic as the influx of freshwater from inland runoff or seawater intrusion from storm surges can lead to fluctuations in salinity which can restructure microbial communities and alter enzymatic activity. Despite the ecological significance of these changes, few studies have explored the effects of short-term salinity shifts on microbial extracellular enzyme activity in coastal waters. This study investigated the effects …

Antibiotic Resistance Patterns In Bacterial Isolates From Mississippi Gulf Coastal Environments, Lawler F. Horn

Honors Theses

Coastal environments host diverse microbial communities that play essential ecological roles but may also serve as reservoirs for antibiotic-resistant bacteria. This study investigated patterns of antibiotic resistance in microbial isolates collected from public beaches along the Mississippi Gulf Coast. A total of 143 bacterial isolates exhibited growth and were included in antibiotic susceptibility screening. High levels of antibiotic resistance were observed, with 137 of 143 isolates showing growth on vancomycin, 124 on amoxicillin, and 102 on erythromycin. Resistance to kanamycin (19/143 isolates) and tetracycline (33/143) was less common. Multidrug resistance was widespread, with 101 isolates (70.6%) resistant to three or …

An Investigation Of Entamoeba Histolytica Chitin Synthases And Other Encystation Factors In Early Encystation, John N. Talledo

All Theses

Entamoeba histolytica is a food-and-water-borne human protozoan pathogen that relies on a two-stage life cycle for successful proliferation outside of the host. E. histolytica exists in its dormant cyst form while outside of its host and converts to the motile trophozoite (amoeba) form in the small intestine. The trophozoites colonize the large intestine to cause symptomatic disease in ~10% of infections, resulting in ~100 million cases of amoebic dysentery each year. Trophozoites can convert back to the cyst form, which is shed in feces to continue the infection cycle.

Currently, there is a lack of understanding of the exact molecular …

Belowground Consequences Of Herbivory In Tomatoes And Cucumbers And Its Lasting Effects, Anthony Ignacio Barrera

Theses, Dissertations and Culminating Projects

Plants recruit soil microorganisms to help mediate biotic stressors such as herbivory, forming dynamic communities in the rhizosphere known as the root microbiome. This study investigated whether artificial herbivory could induce shifts in the root microbiome of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) and whether those shifts could be transferred to subsequent plants as a soil legacy effect. Plants were grown in sterilized or non-sterilized soil with or without simulated herbivory across two experimental phases, with Phase 2 plants receiving inoculum conditioned by Phase 1 plants. Bacterial community composition was assessed via 16S rRNA amplicon sequencing and analyzed using …

Descriptive Comparative Analysis Of Bacteriophage And Auxiliary Metabolic Gene Diversity In Marine And Wastewater Environments, Andrew Crawford

Undergraduate University Honors Capstones

Bacteriophages (phages) are viruses that infect bacteria and play a role in bacterial evolution. Through horizontal gene transfer (HGT), phages integrate parts of their genomes into their bacterial hosts. While the molecular mechanisms of this process are well understood, the evolutionary impacts remain less certain. One evolutionary explanation is that auxiliary metabolic genes (AMGs) modulate host gene expression to favor phage reproduction or improve the host’s survival. AMG can persist in hosts' or phages' genomes across future generations, altering their contributions to the ecosystem and posing a concern for human and environmental health. The objective of this project is to …

Bottles, Butterflies, And Biomass: Recycled Glass Sand, Microbial Additions, And Herbivory Effects On Milkweed Growth, Kealey Skinner

Honors Theses

Plant-soil-microbe interactions are integral components of ecological networks and drive ecosystem function from the bottom-up. Whereas herbivores regulate ecosystem function from the top-down, having opposing and potentially complementary effects on ecosystem function. My thesis sought to understand how below-ground microbial communities contribute to herbivore preference and plant biomass across varied soil substrates. My thesis asked: how do substrate and soil microbial communities influence herbivore preference and plant biomass accumulation on swamp milkweed (Asclepias incarnata)? To address this question, seedlings of A. incarnata were sown in 2.5 cm wide × 10 cm deep pots filled with either natural beach sand or …

Changing Dynamics Of Microbial Communities At A Hydrocarbon Contaminated Site And Methanogenic Interactions With Iron Minerals, Jakob Sell

Masters Theses

Microbial life is not only ubiquitous but also plays a critical role in the geochemical makeup of our planet. While researchers have long studied easily culturable aerobic microbes, the influence of anaerobic life on soils and mineral cycling is less understood. Notably, knowledge about interactions between anaerobic microbes and inorganic elements such as iron has progressed with the discovery that magnetite influences how anaerobic archaea carry out methanogenesis. To better understand anaerobic bacterial metabolisms and how they interact with minerals and subsurface hydrocarbons, we extracted 16S rRNA genes from two adjacent subsurface petroleum plumes, sequenced the DNA, and analyzed it …

Dried Water Treatment Residuals Might Be An Option To Reduce Soluble Reactive Phosphorus Release From Soils, Katie B. Mckay

Biological and Agricultural Engineering Undergraduate Honors Theses

Nonpoint source pollution from agricultural landscapes contributes to freshwater eutrophication, with legacy phosphorus (P) in soils potentially driving soluble reactive phosphorus (SRP) losses to surface waters. The objectives of this study were to evaluate SRP adsorption by dried water treatment residuals (WTRs) produced by Beaver Water District, quantify reductions in soil SRP release across increasing WTR application rates, and compare dried WTR performance to prior WTR studies.

Dried WTRs (~98% solids) were assessed using batch sorption experiments and soil core incubations. Phosphorus sorption was measured by mixing WTRs with CaCl₂ solutions containing increasing SRP concentrations and fitting results to …

Identifying The Role Of Human Dna Polymerase Delta During Human Cytomegalovirus Genome Synthesis, Rachel Laree Dansereau

Dartmouth College Master’s Theses

Human cytomegalovirus (HCMV) is a large double stranded DNA virus and member of the Herpesviridae family. Like all herpesviruses, HCMV presents with characteristics of persistent, lifelong infections that transition between lytic and latent states. The replication of the viral genome is traditionally thought to occur by a rolling circle mechanism, but this model is supported by little evidence. It is known that HCMV actively recruits several host proteins to viral replication compartments (RCs), including proteins involved in the DNA damage response (DDR). The exact mechanisms of how these proteins are used and in what ways they help the virus remain …

Donor And Recipient Microbiome Interactions Determine Functional Outcomes Of Fecal Microbiota Transplantation For Clostridioides Difficile Infection, Sophie A. Millard

All Dissertations

Clostridioides difficile is a major cause of healthcare-associated diarrhea. Infection typically occurs after antibiotic treatment disrupts the gut microbiome, allowing C. difficile to colonize and produce toxins leading to disease (CDI). Standard antibiotic treatments can resolve acute infection but frequently lead to recurrence, highlighting the need for alternative strategies that restore the gut ecosystem. Fecal microbiota transplantation (FMT), the transfer of stool from a healthy donor, has emerged as an effective therapy for recurrent C. difficile infection (rCDI). Understanding the mechanisms underlying the success of FMT for treatment of rCDI could lead to safer, more defined microbial mixtures.

This dissertation …

Urea-Based Boronium Salts As Antimicrobial Agents, Gabriel Allen Merchant

Honors Theses

Quaternary ammonium compounds (QACs) are widely used in disinfectants due to their ability to inhibit the growth of and eliminate microbes. The potency, broad-spectrum activity, and low cost of QACs have made them a cornerstone of modem hygiene. In recent years, QACs have garnered many health and safety concerns due to their overuse and subsequent accumulation in the environment. The increased use of QACs has further led to an increase in antimicrobial-resistant bacteria, making the synthesis of novel antibacterial compounds vital to combat this growing threat. Recent advances in boronium salts offer a unique alternative to address these adverse effects. …

Genetic Screen For Regulators Of Pol4, A Dna Repair Polymerase In Saccharomyces Cerevisiae, Pasang Dolma Sherpa

Theses and Dissertations

In Saccharomyces cerevisiae, DNA polymerase 4 (POL4) is the beta repair polymerase, the product of the POL4 gene, and is involved in base excision repair (BER) and microhomology-mediated end joining (MMEJ). Despite its involvement in these repair pathways and its conservation across eukaryotes, deletion of POL4 shows no detectable phenotype under standard laboratory conditions. I hypothesized that unknown genes act as backup systems, providing redundant activities that allow pol4Δ cells to survive. To test this, a genetic screen for mutants showing synthetic lethality with pol4Δ was implemented. I constructed a strain lacking the POL4 gene and carrying …