SUMMARY Inter-individual variability in host-microbiome interactions contributing to inconsistent results in human clinical studies, presents a major hurdle in determining efficacy and intake recommendations for dietary polyphenols. Gallotannins and other gallated phenolics are present in fruits, spices, and teas, and represent a significant portion of human polyphenol intake. Gallotannins are non-absorbable polymerized gallates that are hydrolyzed and metabolized by the colonic microbiota to gallic acid (GA) and pyrogallol (PG) as primary microbial metabolites. Gut microbial metabolism is a poorly defined determinant of polyphenol pharmacokinetics (PK) and is characterized by inter-individual variability. Preliminary data indicate that: (i) Lactobacillus plantarum (L. plantarum) converts gallotannins to free, absorbable GA and PG; (ii) sulfated and methylated metabolites of GA and PG are readily detected in plasma, urine, and feces of healthy humans after consumption of gallotannins; (iii) PG and its metabolites exhibit potent anti-inflammatory activities both in vitro and in vivo and in human clinical pilot studies; and (iv) metabolism of tannins/gallates is associated with decreased endotoxin and increased short- chain fatty acid (SCFA) production. Central Hypothesis: Inter-individual differential microbial metabolism of GTs into GA and PG is a significant determinant of their anti-inflammatory efficacy in intestinal inflammation. Three integrated specific aims will be pursued as follows: Aim 1 Elucidate GT metabolism in genetic Lp variants and anti-inflammatory signatures in intestinal organoids in vitro using engineered L. plantarum (Lp) strains, including wildtype (LpWT), gallotannase (LpTAN) and gallate decarboxylase (LpDCX-) knockouts, and a double-knockout (LpTAN-/DCX-). Aim 2 Evaluate GT-metabolite signatures within isolated intestinal microbial environments in vivo by applying targeted and unbiased LC-MSn-metabolomics, meta-genomic, and transcriptomic profiling as well as pharmacokinetics in a gnotobiotic mouse model treated with Lp-variants and GTs. Aim 3 Assess pharmacokinetic GT-metabolite signatures and their anti-inflammatory signatures within human intestinal microbial environment as well as microbial adaptation to GTs via targeted meta-genomic, -transcriptomic, and metabolomic analysis in human feces (ulcerative colitis (UC) and controls) +/- LpWT, in mini-bioreactor arrays and in an Mdr1a KO mouse model +/- LpWT stably associated with UC and healthy human fecal microbiota. The host-microbiome-metabolite nexus represents a critical missing link in human clinical trials. Completion of Aims 1-3 will provide a better understanding of causal relationships in the cross-talk between dietary polyphenol intake, and L. plantarum as a probiotic component of the microbiome.