Scholarship & Research
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Item The interaction of heavy metals with the mammalian gut microbiome(Montana State University - Bozeman, College of Agriculture, 2022) Coe, Genevieve Lea; Chairperson, Graduate Committee: Seth Walk; This is a manuscript style paper that includes co-authored chapters.Heavy metals are for the most part, naturally occurring elements found in the environment. Some are essential, meaning they are involved in critical biochemical pathways, in all branches of life. Other heavy metals are non-essential and disrupt metabolic functions in most organisms rendering them toxic. The following research explored the interactions of the mammalian gut microbiome with an essential heavy metal, iron, and a non-essential heavy metal, methylmercury, acquired through the diet. The overarching goal was to define and characterize the influence of gut microbial interactions with heavy metals on host health. Novel experimental designs using murine models were designed to examine 1) the consequences of low iron challenge on the murine gut microbiome and whether host iron availability was affected and 2) the potential influence of the gut microbiome in methylmercury elimination rate and demethylation in conventional, germ-free, gnotobiotic, and humanized mice. Culturing in vitro and toxicity assays, 16S sequencing, deep metagenomic sequencing of human stool, bioinformatic analysis, transcriptional analysis of iron biomarkers, quantification of iron and mercury by ICP-MS and HPLC-ICP-MS methods were performed as well as the use of mouse models to examine iron and methylmercury interactions with the gut microbiome in vivo. Our results from this project indicate that the gut microbiome is significantly affected by loss of iron from the diet, and does not fully recover post-iron repletion, while the host is relatively unaffected by low-iron challenge to the gut microbiome. Methylmercury elimination and demethylation is significantly faster and higher, respectively, in mice with a gut microbiome, providing novel evidence in support of a role for the gut microbiome in methylmercury demethylation and elimination. However, exact mechanisms of microbial interactions with methylmercury in the gut have yet to be elucidated. Our data also suggests the possibility of host-mediated mechanisms of methylmercury demethylation, by yet unknown mechanisms that warrant further exploration.Item Study of diverse host immune responses to viral and bacterial pathogens(Montana State University - Bozeman, College of Agriculture, 2023) Plewa, Jack Bruno; Chairperson, Graduate Committee: Mark Jutila; This is a manuscript style paper that includes co-authored chapters.Brucella abortus is the bacterium that causes brucellosis, an infection transmitted from cattle to people, often through consumption of raw milk and contact with aborted materials. With antibiotic resistance on the rise, phage therapy for bacterial infection may become a useful approach. The direct effects of phage on mammalian cells is important to understand, yet understudied. In vivo delivery of low phage MOI to the mouse lung was more effective at diminishing Brucella burden than higher doses of phage. In an in vitro model of intracellular Brucella infection, low phage MOI was capable of minimizing human THP-1 monocyte infection, but, unexpectedly, use of higher phage MOI diminished this effect. We hypothesized that recognition of these phage preparations may induce an antiviral immune suppressive response that may counteract their anti-bacterial effects. Indeed, when the type I IFN signaling pathway was disrupted in mice, phage treatment was more effective. However, when attempting to induce type I IFN in vitro using both human monocyte and mouse macrophage cell lines, we were unable to stimulate expression of type I IFN with Brucella phage, including in response to a combination of phage and bacteria. We then examined the effect of phage treatment on macrophage cell surface markers that are indicative of activation/differentiation. Interestingly, while Brucella LPS induced expression of CD71 and CD206, the addition of phage suppressed upregulation of these markers. Our discovery of immune suppressive effects of Brucella bacteriophage is an important consideration for using phage as a treatment.