MULTIPLE CHRONIC DISEASES, INCLUDING METABOLIC SYNDROME AND TYPE II DIABETES, ARE KNOWN TO BE ASSOCIATED WITH INDIVIDUALS THAT HAVE A LOW DIVERSITY OF SPECIES IN THEIR GUT MICROBIOMES. FURTHERMORE, WESTERN DIETS ARE STRONGLY CORRELATED WITH LOWER GUT MICROBIOME DIVERSITIES COMPARED WITH INDIGENOUS DIETS FROM MORE TRADITIONAL CULTURES. RECENTLY, MANY RESEARCH GROUPS HAVE DETERMINED THAT: 1) LOSS OF GUT MICROBIOME DIVERSITY IS LINKED TO CONSUMPTION OF THE COMMONLY HIGH-FAT, LOW-FIBER WESTERN DIET, AND 2) IN MICE FED DIETS MIMICKING WESTERN DIETS IN THEIR FIBER CONTENT, GUT MICROBIOTA CAN GO EXTINCT AS MOTHERS FAIL TO TRANSFER THESE MICROBIOTA TO THEIR PUPS. THESE DATA SUGGEST THAT WESTERNIZATION OF DIETS MAY, OVER TIME, REDUCE HUMAN GUT MICROBIOMES IN WAYS THAT MAY INCREASE RISK FOR CHRONIC DISEASE. ALTHOUGH CEREAL BRANS ARE RICH SOURCES OF DIETARY FIBER CARBOHYDRATES AND HAVE TRADITIONALLY BEEN SIGNIFICANT CONTRIBUTORS TO DIETARY FIBER INTAKE IN WESTERN DIETS, A LARGE PERCENTAGE OF BRANS ARE EFFICIENTLY REMOVED FROM HUMAN FOOD STREAMS BY MODERN PROCESSING TECHNIQUES. THIS RESULTS IN LARGE VOLUMES OF LOW-VALUE WASTE BRANS THAT COULD AVAILABLE FOR USE IN DIETARY STRATEGIES TO REDUCE CHRONIC DISEASE BURDENS. FURTHERMORE, THE EFFICIENCY OF MODERN MILLING TECHNIQUES MEANS THAT SMALLER PARTICLES, WHICH ARE GENERALLY PREFERRED BY CONSUMERS FOR THEIR SENSORY PROPERTIES, ARE MUCH MORE EASILY COMMONLY PRODUCED AND CONSUMED. THE IMPACT OF BRAN PROCESSING ON BRAN FIBER FERMENTATION BY THE GUT MICROBIOME IS NOT WELL UNDERSTOOD, AND, CONSEQUENTLY, WE CANNOT PREDICT HOW BRAN SIZES AND PROCESSING MIGHT BE LINKED WITH MICROBIAL FERMENTATION RESPONSES AND THE METABOLIC IMPACTS OF THIS FERMENTATION ACROSS HUMAN MICROBIOMES, WHICH ARE KNOWN TO VARY WIDELY BETWEEN INDIVIDUALS. AS OUR PRELIMINARY DATA SUGGESTS THAT BRANS OF DIFFERING SIZE AND PROCESSING MAY BE FERMENTED DIFFERENTLY BY THE GUT MICROBIOME, RATIONAL PROCESSING OF BRANS FOR MICROBIOME IMPACT MAY REPRESENT A LARGELY-UNTAPPED APPROACH TO MANIPULATE THE GUT MICROBIOME TO PROMOTE HEALTH.THE LONG-TERM GOAL OF THIS PROJECT IS TO DEVELOP A RATIONAL FRAMEWORK FOR USE OF CEREAL BRANS AND THEIR COMPONENT FIBERS TO MAINTAIN GUT MICROBIOME DIVERSITY AND FUNCTION. REMARKABLY LITTLE IS PRESENTLY KNOWN ABOUT HOW DIFFERENT DIETARY FIBER STRUCTURES INTERACT WITH THE GUT MICROBIOTA. PRELIMINARY STUDIES IN OUR LABORATORIES HAVE REVEALED THAT EVEN SUBTLE DIFFERENCES IN BRAN CARBOHYDRATE STRUCTURES RESULT IN SIGNIFICANT DIFFERENCES IN HOW THESE BRANS FERMENT. SPECIFICALLY, OUR DATA SUGGEST THAT 1) FERMENTATION OF OTHERWISE-IDENTICAL WHEAT BRAN PARTICLES DIFFERING IN SIZE RESULTS IN DISTINCT MICROBIAL POPULATIONS AND METABOLIC OUTCOMES, 2) EACH CEREAL BRAN SELECTS FOR DIFFERENT SPECIES FROM THE SAME INITIAL POOL OF MICROBIOTA, 3) FINE STRUCTURAL DIFFERENCES IN WHEAT BRAN FIBERS DETERMINE THE RATE AND OUTCOME OF MICROBIAL FERMENTATIONS. TAKEN TOGETHER, THESE DATA SUGGEST THAT DIFFERENCES IN BRAN TYPE, PROCESSING, AND THE STRUCTU,RE OF THEIR FIBERS MAY EXERT SIGNIFICANT IMPACTS UPON GUT ECOLOGY AND FUNCTION. FROM THESE DATA, WE PROPOSE OUR CENTRAL HYPOTHESIS: THAT SEEMINGLY-MINOR PHYSICAL AND CHEMICAL DIFFERENCES IN BRAN FIBER STRUCTURE DUE TO CEREAL TYPE OR PROCESSING WILL FAVOR DISTINCT MICROBIAL SPECIES AND GOVERN METABOLIC OUTCOMES.WE PROPOSE TO TEST THIS HYPOTHESIS BY SYSTEMATICALLY LINKING BRAN FIBER STRUCTURE AND PROCESSING METHODS WITH MICROBIAL SPECIES AND METABOLIC OUTPUTS THROUGH THE FOLLOWING OBJECTIVES:QUANTIFY THE IMPACTS OF WHOLE CEREAL BRAN TYPE, PARTICLE SIZE, AND MILLING METHODS ON THE DIVERSITY, COMPOSITION AND METABOLIC FUNCTION OF GUT MICROBIOTA IN VITRO.QUANTIFY THE IMPACT OF SOLUBLE BRAN FIBERS (ARABINOXYLANS) CHEMICAL STRUCTURE ON DIVERSITY, COMPOSITION AND METABOLIC FUNCTION OF GUT MICROBIOTA IN VITRO.EVALUATE THE IN VIVO EFFECT OF BRAN FIBER STRUCTURE ON GUT MICROBIOME STRUCTURE AND FUNCTION.THIS PROPOSAL IS HIGHLY RESPONSIVE TO USDA IMPROVING FOOD QUALITY PROGRAM AREA GOALS BY INCREASING UNDERSTANDING OF HOW BRANS, BRAN PROCESSING, AND SOLUBLE BRAN FIBERS IMPACT THE GUT MICROBIOME AND, IN TURN, INFLUENCE NUTRITIONAL OUTCOMES AND OVERALL HOST PHYSIOLOGY. WE EXPECT TO GENERATE FUNDAMENTAL KNOWLEDGE THAT WILL ENABLE USE OF BRAN FIBERS IN DIETARY STRATEGIES FOR TARGETED IMPROVEMENTS IN GUT MICROBIOME COMPOSITION AND FUNCTION WITH THE GOAL OF IMPROVING NUTRITIONAL BENEFIT AND REDUCING CHRONIC DISEASE BURDENS.