Microbiology Commons^™

Microbial Community Structure In Global Soils, Matthew Jabro

CMC Senior Theses

Soil harbors the most diverse microbial communities on Earth, yet whether predictable community types exist across biomes and whether taxonomic composition encodes habitat of origin remain open questions at global scale. This thesis addresses both questions by applying unsupervised clustering and supervised classification to transformed 16S ribosomal RNA (rRNA) amplicon profiles from two independent datasets: the global topsoil survey of Bahram et al. (193 samples) and the Earth Microbiome Project (EMP) soil subset of Thompson et al. (2,209 samples). Application of a sample clustering method based on a mixture of Gaussian Graphical Models (MixGGM) identified 19 clusters in the topsoil …

Characterizing Gut Microbial Communities And Symbiont-Mediated Detoxification In Herbivorous Insects, Rachel C. Vargas

Biology Dissertations

Insect gut bacteria are vital contributors to host physiology, yet the broader prevalence and fitness implications of symbiont-mediated detoxification remain poorly understood. This thesis investigates these dynamics across three research chapters. Chapter 1 uses 16S rRNA sequencing to characterize how grasshopper gut microbial communities vary across species, dietary breadths, and gastrointestinal segments. Chapter 2 evaluates the detoxification capacity of over 150 bacterial isolates from diverse herbivores against the plant allelochemicals phenethyl isothiocyanate, rutin, and chlorogenic acid to determine if host dietary specialization predicts microbial metabolic ability. Finally, Chapter 3 employs fitness bioassays to test whether inoculating generalist herbivores with detoxifying …

Development Of A Semi-Mechanistic Pharmacokinetic-Pharmacodynamic Model For Beta-Lactam Antibiotic Combination Against Enterococcus Faecalis Based On Time-Kill Assays To Predict Drug Disposition And Guide Dosing Strategy In A Severe Renal Impairment Population, Ruhma Zia Khan

Selected Full-Text Dissertations 2020-

Bacterial resistance to antibiotics continues to be a global health problem, limiting antibacterial therapy against infective endocarditis caused by Enterococcus faecalis. To overcome increasing resistance, dual beta-lactam therapy has been advocated as an alternative regimen for treatment – the synergistic activity against E. faecalis demonstrated to be effective. Currently, ampicillin plus ceftriaxone is the standard of care, but the practical application of this therapy is limited by ampicillin’s poor stability in solution at room temperature. A synergistic combination of penicillin plus ceftriaxone shows promise due to penicillin’s superior stability at ambient temperature, but ceftriaxone’s potential to cause hepatoxicity further limits …

Use Of Enterococcus Faecalis And Cetylpyridinium Chloride In Altering Canine Mouth Microbiome, Quigley D. Espinola, Scarlet Renner, Curtis Cline, Sofia Lopez-Orenday, Alex Yasumatsu

Humboldt Journal of Microbiology

Like most mammals, canines have copious amounts of bacteria in their oral cavity. While some of these bacteria are beneficial and even necessary to their health, overgrowth of harmful bacterial strains can lead to plaque buildup and gum disease. To combat plaque and bacteria, several products are marketed towards canines. In this study, we aim to explore how the microbiome of the canine mouth is affected by a potential probiotic, Enterococcus faecalis, and an antimicrobial water additive found in dog mouthwash products, Cetylpyridinium chloride monohydrate (CCM). We hypothesized that both would be successful in their ability to decrease harmful bacteria. …

Exploring The Link Between Soil Microbes, And Land Use Through A One Health Lens, Yaw A. Antwi

Master's Theses or Doctor of Nursing Practice

The diversity of microbes within the soil plays an essential role in soil ecosystem

functioning. However, these microbes may also serve as environmental reservoirs for antibiotic resistance genes. The study examined the diversity of bacteria that are found in soil across Rural/Agricultural and Rural/Nonagricultural landscapes within some selected counties in Kansas and its associated antibiotic resistance genes taxa. A total of twenty-four soil samples was collected and analyzed using 16S rRNA gene amplicon sequencing which targeted the V3-V4 regions. Statistical analysis revealed that the alpha diversity metrics (Chao1 richness and Shannon evenness) showed no significant difference in microbial structure (p=0.693, …

The Role Of Tumor Microenvironment In Glioblastoma Multiforme(Gbm) Therapeutic Resistance, Kwesi E. Taylor

Master's Theses or Doctor of Nursing Practice

Despite significant advances in cancer research and treatment, Glioblastoma multiforme (GBM) remains one of the most difficult cancers to treat effectively, with minimal improvement in long-term survival rates over the past few decades. This is largely attributed to tumor heterogeneity and the ability of tumor cells to develop adaptive resistance mechanisms supported by the tumor microenvironment (TME). Although the TME is recognized as a key contributor to tumor progression and therapeutic resistance, the underlying molecular pathways and regulatory genes remain incompletely understood. This study investigated the role of the tumor microenvironment in GBM therapeutic resistance using a bioinformatics approach. Single-cell …

The Effect Of The Affordable Care Act Medicaid Expansion On The Risk Of Hospital Closure And Adolescent Hpv Immunization In Rural Counties, Juliette Des Rosiers

Scripps Senior Theses

From 2005 to 2025, over 200 rural hospitals shut their doors, often citing increased operational costs, staffing shortages, low patient volume, regulatory barriers, financial challenges exacerbated by the COVID-19 pandemic, and uncompensated care as common contributors to the closures. Rural patients are often referred by their primary care physician to a hospital for regular immunizations, since smaller clinics have less capacity to provide immunizations due to a shortage of pediatricians and limited vaccine stock. A crucial vaccine that is not required by schools and underutilized in rural areas is that against human papillomavirus (HPV), a virus that infects cutaneous and …

Lead Biosorption By Oceanobacillus Profundus Kbz 3-2: Strategies For Bioremediation Systems In Kabwe, Danielle S. Desmarteau

Scripps Senior Theses

Lead contamination remains a significant global public health concern, particularly in Kabwe, Zambia, the site of a former lead mining operation. Bioremediation, which utilizes biological materials and processes to remove environmental contaminants, represents a promising approach for addressing lead pollution. However, the development of effective bioremediation systems requires a detailed understanding of the mechanisms underlying metal removal and the feasibility of implementation in low-resource settings. Oceanobacillus profundus KBZ 3-2, a bacterium isolated from Kabwe mine waste, has demonstrated the ability to remove lead from aqueous environments. This study proposes to investigate the mechanism of lead biosorption by this organism, …

From Theory To Ecosystems: Exploring Biodiversity And Ecosystem-Function In Pitcher Plant (Darlingtonia Californica) Microbial Communities, Gavin Sutter

Cal Poly Humboldt theses and projects

The relationship between biodiversity and ecosystem-function (BEF) has been a central focus of ecological research for the last three decades, yet the role of space in shaping BEF relationships remains relatively unknown. Research has shown that community diversity and composition can strongly influence productivity, nutrient cycling, and decomposition, but much of this work treats communities as spatially isolated, leaving open how dispersal and other spatial processes shape BEF at broader scales. To begin addressing this gap, I used microbial communities inhabiting Darlingtonia californica pitcher plant leaves to evaluate how spatial organization and successional change shape biodiversity and ecosystem-functioning. I quantified …

Bacterial Community Function In Pitcher Plant Leaves As An Experimental And Mathematical Model Of Functional Dynamics, Amelia Jackson

Cal Poly Humboldt theses and projects

This work looks at two different sites with differing abiotic factors in measures of altitude, temperature and precipitation. The site with higher altitude, larger temperature range, and lower precipitation, located in Plumas National Forest (Quincy, CA), had a flat BEF trend that suggests functional redundancy The site with lower altitude, more moderate temperatures, and higher precipitation located in Six Rivers National Forest (Gasquet, CA), also had a flat BEF trend. These abiotic factors could correlate to the significantly different bacterial compositions between sites. The second portion of this work is modeling the host antagonist relationship between Eyxra moths and their …

Pipeline Corrosion And Relevant Microbial Influence, Renee E. Bamberger

Williams Honors College, Honors Research Projects

This study investigated the role of microbial activity and oxygen availability in the corrosion of carbon steel pipelines with a focus on microbially influenced corrosion (MIC). Sediment collected from Old Woman Creek, Ohio, was used to simulate natural soil conditions, and carbon steel coupons were incubated under four treatments: nonsterile oxic, nonsterile anoxic, autoclaved oxic, and autoclaved anoxic over 85 days. Corrosion was assessed through mass loss measurements and the analysis of pH, sulfate, chloride, and dissolved iron concentrations. The greatest mass loss was observed in autoclaved oxic conditions, contrary to the initial hypothesis that microbial activity would greatly enhance …

Investigating The Anti-Apoptotic Properties Of The N-Terminus Of The Chlamydia Trachomatis Effector Tarp, Kasey S. Jordan

Graduate Studies Theses and Dissertations 2026

As the most prevalent bacterial STI in the United States and leading cause of infection-related blindness worldwide, the obligate intracellular bacteria, Chlamydia trachomatis (Ct), poses a significant threat to public health. As an obligate intracellular bacteria, invasion of the host cell is a crucial step in Chlamydia’s developmental cycle. To drive invasion, Ct injects prepackaged effectors into the host cell using a T3SS. An early Chlamydial effector, translocated actin recruiting phosphoprotein, or Tarp, interacts with host cell actin to promote invasion, mediated via Tarp’s C-terminal region. Although the function of Tarp’s C-terminus is well defined, the Tarp’s N-terminus …

Evaluation Of Mycoplasma Genitalium Positivity And Co-Infection With Chlamydia Trachomatis And/Or Neisseria Gonorrhoeae At Various Care Sites Across The United States, Rebecca Lillis, Rodney Arcenas, Christy M. Boraas, Steven E. Chavoustie, Lashonda Crane, Nicole D'Empaire, Aaron C. Ermel, Glenn Harnett, Federico Hinestrosa, Stacey House, Joseph Miller, Anthony Mills, Ronald Poblete, Stephen Young, Barbara Van Der Pol

School of Medicine Faculty Publications

OBJECTIVES: We evaluated Mycoplasma genitalium (MG) positivity and co-infection with Chlamydia trachomatis (CT) and/or Neisseria gonorrhoeae (NG), based on results from a trial assessing clinical performance of the Cobas® Liat CT/NG/MG point-of-care test. METHODS: A prospective, US, multicenter, noninterventional study assessed MG positivity in prospective urine samples (male) and clinician-collected vaginal swabs (female) from symptomatic/asymptomatic patients aged ≥14 years attending various clinical settings. Participants were designated positive or negative for MG, CT, and NG based on combined results from three US Food and Drug Administration-approved assays and one laboratory-developed test. MG co-infection with CT and/or NG was assessed. RESULTS: Among …

Repurposing Cyclin-Dependent Kinase Inhibitors For The Discovery Of Novel Antiplasmodial Compounds, Ritam Bhowmik

Honors Undergraduate Theses

Malaria remains a major global health burden with over 282 million cases annually and rising resistance to artemisinin-based combination therapies. Plasmodium falciparum, the most lethal malaria parasite species in humans, relies on tightly regulated cell cycle progression during replication within red blood cells. Cyclin-dependent kinases (CDKs) are central regulators of eukaryotic cell division and transcription, and several CDK-like enzymes in P. falciparum, including Pfmrk and PfPK6, are essential for parasite growth and structurally distinct from human kinases. This study evaluated whether commercially available human CDK inhibitors (CDKIs) targeting cancer pathways could be repurposed as novel antimalarial compounds. A library of …

Quantifying Amendment Impact On Microbial Respiration Rate, Qwynn Starrwalker

Honors Undergraduate Theses

Wetlands play a critical role in the global carbon cycle by acting as carbon sinks, where the flooded anaerobic conditions cause slow microbial respiration compared to other soils. Comparatively more carbon is stored in the soil as organic matter than is released as carbon dioxide (CO₂). Making wetland pools of soil organic matter less available to microbes for respiration could reduce overall atmospheric CO₂ and slow global warming. This study examined the effect of kaolinite, goethite, and lime on microbial respiration rates in wetland soils under alternating hydrologic conditions. Homogenized soil from a cypress dome was separated …

The Importance Of The Proline Residue In The Ldiapa Motif Of Cholera Toxin, Akash Bharathan

Honors Undergraduate Theses

Cholera is currently on its seventh global pandemic, disproportionately affecting developing countries. Vibrio cholerae, the bacterial etiologic agent, is able to cause infection by adhering to intestinal epithelial cells and secreting cholera toxin (CT), an AB-type exotoxin that dysregulates signaling pathways. Previous research by the Teter lab has shown that Hsp90, a host cytosolic chaperone, is required for CT to enter the cytosol where it produces toxic effects. Hsp90 binds to CT at two specific motifs, RPPDEI and LDIAPA. The prolines in the RPPDEI motif are essential for binding, but the proline in the LDIAPA has yet to be …

Investigating The Interaction Of Gram-Positive Lactobacillus Species With Mucin In The Context Of Barrett's Esophagus, Ritisha Suresh

Honors Undergraduate Theses

Gastroesophageal Reflux Disease (GERD) can progress to the precancerous Barrett’s Esophagus (BE) condition, in which the normal esophageal squamous epithelium is replaced with a columnar epithelium containing goblet cells. Mucins, sticky substances, are secreted in response to bile acid exposure during reflux episodes to protect the esophageal epithelium. Goblet cells secrete these mucins, which can also scaffold microbial colonization. Probiotic Lactobacillus bacteria can use glycosidase enzymes to process mucin and metabolize them into their component sugars (glycans). This project aims to identify the role of the Lactobacillus-mucin interaction in BE, as glycan availability could confer an advantage to Lactobacillus …

Assessing The Impact Of Storing Water Samples At Ambient Temperature On Plankton Metabarcoding, Stephanie N. Lievano

Honors Undergraduate Theses

Increasing incidence of Harmful Algal Blooms (HABs) has led to fish kills, air quality hazards, and economic impacts. One economic impact is on tourism, one of the main sources of Florida’s income, where billions of dollars are lost to such events. The Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute (FWC-FWRI), with the help of collaborators, collects water samples from across the state for HAB monitoring. These samples are stored at ambient temperature for up to 24 hours which could directly affect data analyses. Here, in collaboration with FWRI-FWC, I investigated whether this storage technique affects plankton …

Coordinating The Layers: Regulation Of Peptidoglycan Synthesis And Cell Wall Assembly In Mycobacterium Smegmatis By Murj And Pgfa, Karen Emmanuella Samaga-De-Tembiwa

Biology Dissertations

The mycobacterial cell envelope consists of three covalently linked layers whose synthesis must be coordinated to maintain structural integrity during polar growth. While the biosynthetic enzymes for each layer are well characterized, the molecular mechanisms that coordinate synthesis across layers have remained poorly understood. This thesis investigates two essential transmembrane proteins, PgfA and MurJ, that regulate peptidoglycan metabolism in Mycobacterium smegmatis and provide new insight into how mycobacteria synchronize cell wall assembly.

We present evidence that PgfA functions as a bifunctional regulator that links peptidoglycan metabolism to the availability of trehalose monomycolate (TMM), a key mycolic acid precursor. Through epistasis …

Characterizing The Human Metapneumovirus Matrix Protein And Its Role In Infection, Chase J. Heim

Theses and Dissertations--Molecular and Cellular Biochemistry

Human metapneumovirus (HMPV) causes severe respiratory tract infections in all cohorts, but especially in vulnerable groups such as children, older adults, and the immunocompromised. The matrix (M) protein of HMPV, like the M proteins of other members of the Mononegavirales order, is involved in virus assembly and budding. However, other functions of the HMPV M protein have yet to be elucidated. To investigate these various functions of the M protein, we used a peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) antisense agent designed to block translation of the M gene to reduce M expression during infection. Treatment with varying concentrations of an …