Bacteriology Commons^™

Understanding The Role Of Toxs As A Bile Sensing Component Of The Toxrs Virulence Regulatory System In Vibrio Spp., Minje Kim

Dartmouth College Ph.D Dissertations

Pathogenic Vibrio bacteria, such as V. cholerae and V. parahaemolyticus, colonize in the human small intestine to cause severe gastrointestinal disease. During the infection, these bacteria encounter bile salts, antimicrobial cholesterol metabolites secreted into the intestine. Pathogenic Vibrio species have evolved to utilize bile salts as signals to regulate virulence. The signaling depends in part on ToxRS, a conserved co-component transmembrane transcription regulator. ToxRS consists of the transcription factor ToxR and its membrane-tethered binding partner ToxS. ToxS is required for ToxR stability and full transcriptional activity. Although bile salts are known to influence ToxRS-dependent virulence gene expression, the molecular …

Evolution Of Antibiotic Responses During Chronic P. Aeruginosa Infections In The Human Lung, David Frank Ritz

Dartmouth College Ph.D Dissertations

Typical antibiotic susceptibility testing (AST) of microbial samples is performed in homogeneous cultures in batch environments, which does not account for the highly heterogeneous and dynamic nature of antibiotic responses. The most common mutation found in P. aeruginosa lineages evolved during chronic cystic fibrosis infections in the human lung, a loss of function of repressor MexZ, increases basal levels of multidrug efflux MexXY, but does not increase resistance by traditional minimal inhibitory concentration (MIC) assays. Here, we use single cell microfluidics to show that P. aeruginosa’s response to aminoglycosides is highly heterogeneous, with only a subpopulation of cells surviving exposure. …

Biofilm Architecture Determines Proliferation Of Phages And Plasmids, James B. Winans

Dartmouth College Ph.D Dissertations

This thesis explores how biofilm architecture determines the spread and ecological consequences for the bacteria-dependent genetic elements phages and plasmids. Using Escherichia coli and Vibrio cholerae as model microbes, and the genetic elements T7 phages, λ phages, and conjugative plasmid pED208, we investigate how spatial structure influences phage infection dynamics, plasmid transfer, and interbacterial interactions within biofilms. We show that densely packed biofilms can protect sensitive bacteria from phage exposure and modulate competitive outcomes between obligately lytic and temperate phages. We find that entirely different outcomes can coöccur within microns of each other dependent on biofilm structure. We also demonstrate …

Investigating The Mechanisms Of Microbial Interactions Using A Model Cystic Fibrosis Polymicrobial Community, Bassam El Hafi

Dartmouth College Ph.D Dissertations

Cystic fibrosis (CF) airway microbial communities are complex ecosystems where interspecies interactions influence pathogen survival and disease progression. We leverage a CF-relevant in vitro four-species model composed of Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus sanguinis, and Prevotella melaninogenica, alongside a microbiome dataset with over 4,000 respiratory samples from publicly available sequencing data of CF patient samples, to explore the dynamics of microbial interactions in CF. On a broader scale, we performed microbial network analysis to examine how the latest modulator therapy, elexacaftor/tezacaftor/ivacaftor (ETI), might influence CF microbial communities. Our analysis revealed a reduction in node connections and …

Modeling The Cystic Fibrosis Intestinal Environment To Study Microbial Interactions, Kaitlyn Emma Barrack

Dartmouth College Ph.D Dissertations

The microbiome of the cystic fibrosis (CF) intestine is altered significantly in structure and function beginning in early life. Key taxa associated with health, digestion and immune-training are reduced in abundance, including but not limited to Bacteroides, Faecalibacterium, Akkermansia, Ruminococcus and other short-chain fatty acid producers. Conversely, there is an expansion of microbes with pathogenic potential, such as Escherichia, Veillonella, Pseudomonas and Staphylococcus. The shifts in microbiota composition direct community-wide changes with differences in beta diversity by genotype, whereby children with CF (cwCF) exhibit significantly different gut microbial compositions compared to nonCF children. Additionally, shifts in microbiota structure often …

Biochemical And Molecular Analysis Of Anr-Dependent Microoxic Fitness Factors In Pseudomonas Aeruginosa, Stacie E. Balsam

Dartmouth College Ph.D Dissertations

Pseudomonas aeruginosa is a prominent opportunistic pathogen that is often found in microoxic environments like sites of infection and colony biofilms. P. aeruginosa can grow at oxygen (O2) at concentrations as little as 3 μM and also grows anaerobically by generating energy using nitrate as an alternate electron acceptor. An important way P. aeruginosa adapts to low O2 is through Anr, a transcription factor that upregulates many genes important for microoxic and anoxic fitness.

Specifically, Anr regulates mhr which encodes a hemerythrin protein (Mhr) that binds O2 with affinities relevant to microoxia and is also necessary for full fitness of …

Fleq And Gac/Rsm-Mediated Regulation Of Biofilm Formation And Swarming Motility In Pseudomonas Fluorescens, Alexander Benito Pastora

Dartmouth College Ph.D Dissertations

Pseudomonas fluorescens is a gram-negative Gammaproteobacterium that survives and persists in diverse environments. This survivability is dependent on the bacterium’s ability to form a biofilm. Within Pseudomonas fluorescens, biofilm formation is a complex and dynamic process involving multiple protein- and polysaccharide-based components which each individually serve a specific purpose. Of these components, the repeats-in-toxin (RTX) adhesins LapA and MapA are critical for biofilm formation. Specifically, LapA is important for initial establishment of a biofilm and MapA is important in forming a fully mature biofilm. Deployment of the RTX adhesins during biofilm formation is a highly coordinated process involving multiple …

Social Interactions And Spatial Structure Drive Community Assembly Of Bacterial Biofilm, Matthew C. Bond

Dartmouth College Ph.D Dissertations

Despite the critical nature which microbial communities play in the natural world and human civilization, the breadth of understanding remains shallow. Challenged by scale, high variability between environments, and extensive diversity, microbial ecologists strive to understand connections between a community’s structure and function, as well as the ecological and evolutionary mechanisms underlying observed natural patterning of communities. Biofilms are the predominate mode of growth for microbial communities—characterized by cellular attachment to a surface via a self-produced matrix and heterogeneous structure, often resulting in a primary growth front along the biofilm surface due to differential access to bulk nutrients (cite). This …

Causes And Consequences Of Lasr Mutant Selection In Pseudomonas Aeruginosa Populations, Dallas L. Mould

Dartmouth College Ph.D Dissertations

Change is the only constant in life, and these changes, though random in nature, can have consequences. Quorum sensing is heterogeneous in phenotype and prone to negative selection. In P. aeruginosa, the regulator LasR is frequently non-functional in phylogenetically diverse isolates. Through repeated experimental evolution and mathematical modeling, we show that differences in growth enable lasR mutant evolutionary success and this requires a system enabling metabolic choices, known as carbon catabolite repression (or catabolite repression). The differences in catabolite repression between wild type and lasR mutants enable altered metabolite preferences, and the resulting differences in metabolic states enable intraspecies …