A designed synthetic microbiota provides insight to community function in Clostridioides difficile resistance.

Clostridioides difficile, a major cause of antibiotic-associated diarrhea, is suppressed by the gut microbiome, but the precise mechanisms are not fully described. Through a meta-analysis of 12 human studies, we designed a synthetic fecal microbiota transplant (sFMT1) by reconstructing microbial networks negatively associated with C. difficile colonization. This lab-built 37-strain consortium formed a functional community suppressing C. difficile in vitro and in animal models. Using sFMT1 as a tractable model system, we find that bile acid 7α-dehydroxylation is not a determinant of sFMT1 efficacy while one strain performing Stickland fermentation-a pathway of competitive nutrient utilization-is both necessary and sufficient for the suppression of C. difficile, replicating the efficacy of a human fecal transplant in a gnotobiotic mouse model. Our data illustrate the significance of nutrient competition in suppression of C. difficile and a generalizable approach to interrogating complex community function through robust methods to leverage publicly available sequencing data.