MOST (&GT;90%) BACTERIA IN THE GUT MICROBIOME ARE UNCULTURED AND KNOWN ONLY FROM RIBOSOMAL DNA SEQUENCES. THESE SEQUENCES DO NOT REVEAL THE METABOLIC ACTIVITIES OF A BACTERIUM, REPRESENTING A CHALLENGE FOR IDENTIFYING THE ROLE OF UNCULTURED BACTERIA IN ANIMAL NUTRITION AND DISEASE. FOR EXAMPLE, SEQUENCING CAN LINK THE ABUNDANCE OF AN UNCULTURED BACTERIUM WITH IMPROVED ANIMAL FEED EFFICIENCY, BUT IT CANNOT REVEAL ITS METABOLIC ACTIVITIES AND EXACT ROLE IN IMPROVED EFFICIENCY. A NEW TOOL, RELYING ON FLUORESCENT SUBSTRATE ANALOGS, COULD REVEAL AN UNCULTURED BACTERIUM'S MOST FUNDAMENTAL METABOLIC CHARACTERISTIC--WHAT SUBSTRATES IT USES. OUR CENTRAL OBJECTIVE IS TO DEVELOP A TOOL THAT INVOLVES 1) INCUBATING RUMEN BACTERIA IN FLUROSCENT GLUCOSE ANALOGS, 2) SEPARATING OUT CELLS THAT TAKE UP ANALOGS WITH FLUORESCENCE-ACTIVATED CELL SORTING, AND 3) 16S RDNA SEQUENCING OF THOSE CELLS, REVEALING BACTERIAL SPECIES (OTUS) THAT UTILIZE GLUCOSE. BASED ON PRELIMINARY DATA, WE ESTIMATE THAT OUR TOOL CAN IDENTIFY 2,250 RUMEN SPECIES AS GLUCOSE UTILIZERS--SEVERAL FOLD MORE THAN ALL SPECIES DISCOVERED IN THIS HISTORY OF CULTURING THIS COMMUNITY. THE TOOL COULD BE ADAPTED TO OTHER FLUORESCENT SUBSTRATE ANALOGS AND AGRICULTURALLY-IMPORTANT COMMUNITIES (SOIL, NATURAL WATERS, PLANTS); THUS, IT COULD CAUSE A PARADIGM SHIFT IN IDENTIFYING METABOLIC ACTIVITIES OF UNCULTURED BACTERIA. IT WOULD HELP DETERMINE THE ROLE OF SPECIFIC GUT BACTERIA IN ANIMAL NUTRIENT EFFICIENCY AND DISEASE, FOR EXAMPLE, AND HAS RELEVANCE TO MANY PROJECTS ADDRESSING THE MICROBIOME.