THE HUMAN COLON HARBORS TRILLIONS OF MICROORGANISMS, AND THE INTERACTIONS OF THESE MICROORGANISMS WITH THE HOST INFLUENCES HEALTH. ALTHOUGH IT IS KNOWN THAT DIETARY FIBER BROADLY AFFECTS THE MICROBIOME, THERE IS INSUFFICIENT KNOWLEDGE REGARDING HOW INSOLUBLE FIBERS WITH SPECIFIC PHYSICAL STRUCTURES INFLUENCE THE TAXONOMIC COMPOSITION OF THIS COMPLEX ENVIRONMENT. THE OVERALL OBJECTIVE OF THIS PROJECT IS TO DETERMINE THE IMPACT OF DIETARY FIBER PHYSICAL STRUCTURE, INVESTIGATED THROUGH CROSS-LINKING ARABINOXYLANS WITH DIFFERENT FERULIC ACID CONTENT AND ARABINOSE TO XYLOSE RATIOS, ON TAXONOMIC SHIFTS IN THE COLONIC MICROBIOME. THE CENTRAL HYPOTHESIS IS THAT FIBERS WITH GREATER DEGREE OF PHYSICAL STRUCTURE (CROSS-LINKING) WILL INCREASE THE POPULATIONS OF BUTYROGENIC BACTERIA IN THE COLONIC MICROBIOME AS THESE MICROORGANISMS HAVE A COMPETITIVE ADVANTAGE TO METABOLIZE SUCH FIBERS. RESULTS OF THIS PROJECT WILL LEAD TO GREATER UNDERSTANDING OF FIBER UTILIZATION BY BACTERIA IN THE COLONIC MICROBIOME BY INTEGRATING MICROBIAL METABOLISM, A NOVEL APPROACH TO SYSTEMATICALLY MODIFY THE DEGREE OF CROSS-LINKING OF ARABINOXYLANS, AND MATHEMATICAL MODELING. THIS APPROACH WILL BE USED TO DEVELOP A PREDICTIVE RELATIONSHIP BETWEEN FIBER STRUCTURE AND TAXONOMIC SHIFTS OF THE MICROBIOME. THIS COULD HELP ENABLE TARGETED SHIFTS IN THE GUT MICROBIOME, ADVANCING THE AFRI PRIORITY AREA OF FOOD SAFETY, NUTRITION, AND HEALTH. THE PROJECT SUPPORTS THE CAREER DEVELOPMENT OF THE PROJECT DIRECTOR THROUGH A SPECIFIC PLAN TO STRENGTHEN RESEARCH, COMMUNICATION, AND LEADERSHIP SKILLS AND FOSTER A TRANSITION TO CAREER INDEPENDENCE. THIS PROJECT MEETS THE AFRI-EWD GOALS OF ADVANCING SCIENTIFIC KNOWLEDGE AND DEVELOPMENT OF THE PROJECT DIRECTOR AS A FUTURE LEADER IN THE AGRICULTURAL RESEARCH WORKFORCE.