Abstract Patients with ulcerative colitis (UC), an inflammatory bowel disease (IBD), have an increased risk of developing colitis-associated colorectal cancer (CAC). Human gut microbiome composition has recently been associated with a wide array of diseases, including IBD and colorectal cancer. Studies have shown that gut microbiota could influence colon epithelium to initiate or promote colorectal cancer development directly or indirectly. However, little is known on the structure and function of the microbiota in CAC and how they implicate the development of CAC at the molecular level. In this study, we will investigate the role of microbiota in the development of CAC, as well as the molecular events underlying the interplay of microbiota and host response. The project builds upon our previous studies in examining the genomic instabilities and proteome alterations in the colon epithelium during the pathogenesis of IBD-CAC, and will focus on the mechanistic and functional involvement of the microbiome and their components in the modulation (by protective bacteria) or activation (by tumorigenic bacteria) of CAC development. Specifically, we will investigate the implication of mucosa- associated microbiota in CAC by an integrated approach using three model systems, including clinical specimens (Aim 1), in vitro microbial cultivation and organoid models (Aim 2), and in vivo mouse model (Aim 3). Our integrative, state-of-the-art approach will characterize the composition, functional genes and pathways of the microbiome implicated in CAC, and the impact of microbiota on colon mucosa. By studying the gut microbiota and its interplay with the colon host using novel approaches and cutting-edge technology, our study has significant translational potential that could lead to establishing the gut microbiome as predictors of CAC risk and aid in developing approaches for CAC prevention and detection in IBD patients.