Systematic characterization of microbes in several tumors including colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC) has revealed the presence of multiple species of intracellular bacteria within tumors. However, there is limited knowledge on how these bacteria colonize tumors, how they survive inside host cells, how they modulate host cell phenotypes, and if their elimination should complement cancer therapy. This is, in part, due to the lack of representative animal models, challenges in co-culture of host epithelial cells and bacteria, and limited resolution of available analytical techniques to study host-microbial interactions. I have addressed these challenges by harnessing multiple technologies from microbiology, genetic engineering, tissue engineering, and microfluidics, in order to investigate the role of an emerging oncomicrobe, Fusobacterium nucleatum, in the tumor microenvironment (TME). F. nucleatum is a Gram-negative, anaerobic bacterium that is normally found within the oral cavity. However, its selective enrichment in CRC and PDAC tumors is correlated with poor clinical outcomes. My work along with collaborators in the Verbridge, Slade, and Lu labs at Virginia Tech has revealed a multifactorial impact of F. nucleatum in influencing cancer progression. First, in CRC, we discovered that F. nucleatum infection of host cancer cells induced robust secretion of select cytokines that increased cancer cell migration, impacted cell seeding, and enhanced immune cell recruitment. In PDAC, we uncovered additional cytokines that were secreted from both normal and cancerous pancreatic cell lines upon infection with F. nucleatum that increased cancer cell proliferation and migration via paracrine and autocrine signaling, notably in the absence of immune cell participation. In order to examine the contribution of a hypoxic TME on infection dynamics, we used a multi-omics approach that combined RNA-seq and ChIP-seq of H3K27ac to determine epigenomic and transcriptomic alterations sustained within hypoxic CRC cells upon infection with F. nucleatum. Our findings revealed that F. nucleatum can subvert host cell recognition in hypoxia and can modulate the expression of multiple cancer-related genes to drive malignant transformation. Insights gained from this research will pave the way for future studies on the impact of the tumor microbiome in cancer and will identify novel targets for therapy and clinical intervention to control bacteria-induced exacerbation of cancer. / Doctor of Philosophy / Colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC) are the second and third leading causes of cancer death in the United States, respectively. Recent systematic characterization of various tumor types revealed the presence of distinct bacteria within tumors. However, there is limited knowledge on how these bacteria colonize tumors, how they survive inside host cells, how they modulate host cell phenotypes, and if their elimination should complement cancer therapy. This is, in part, due to the lack of representative animal models, challenges in developing host cell-microbe co-culture models, and limited resolution of available analytical techniques to study host-microbial interactions. I have addressed these challenges by harnessing multiple technologies from microbiology, genetic engineering, tissue engineering, and microfluidics, in order to investigate the role of an emerging cancer-associated microbe, Fusobacterium nucleatum, in the tumor microenvironment (TME). F. nucleatum is a microbe commonly found within the oral cavity. However, clinical studies revealed that selective enrichment of F. nucleatum in CRC and PDAC tumors significantly correlated with poor prognosis. My work along with collaborators in the Verbridge, Slade, and Lu labs at Virginia Tech has revealed a multifactorial impact of F. nucleatum in influencing cancer progression. First, in CRC, we discovered that F. nucleatum invasion of host cancer cells induced the secretion of select proteins called cytokines that cells use to signal and communicate with each other. These cytokines directly stimulated the cell migration of host cancer cells which is usually associated with increased cancer aggressiveness. In PDAC, F. nucleatum infection induced the secretion of additional cytokines from both cancer cells and normal cells that, in addition to cell migration, impacted the proliferation of cancer cells, another feature of aggressive cancers. F. nucleatum usually thrives in a low oxygen environment that is prevalent in cancer tissue and hence, we examined how a low oxygen environment can influence infection dynamics using sequencing technologies that probe the genomic constitution within cells. Our findings revealed that F. nucleatum can escape recognition in low oxygen environments and can modulate the expression of multiple cancer-related programs within the cell to drive cancer progression. Insights gained from this research will pave the way for future studies on the impact of the tumor-associated microbes in cancer and will identify novel targets for therapy and clinical intervention to control bacteria-induced exacerbation of cancer.