Fecal microbiota transplantation (FMT) is a promising therapy for inflammatory bowel disease (IBD) via rectifying gut microbiota. The aim of this study was to identify a mechanism of how specific bacteria-associated immune response contributes to alleviated colitis. Forty donors were divided into high () and low () groups according to the diversity and the abundance of and by 16S rRNA sequencing. FMT was performed on dextran sulfate sodium (DSS)-induced colitis in mice. Mice with colitis showed significant improvement in intestinal injury and immune imbalance after FMT with ( < 0.05). and were identified as targeted strains in donor feces by real-time PCR and droplet digital PCR. Mice with colitis were treated with mono- or dual-bacterial gavage therapy. Dual-bacterial therapy significantly ameliorated intestinal injury compared with mono-bacterial therapy ( < 0.05). Dual-bacterial therapy increased the M2/M1 macrophage polarization and improved the Th17/Treg imbalance and elevated IL-10 production by Tregs compared with the DSS group ( < 0.05). Metabolomics showed increased abundance of lecithin in the glycerophospholipid metabolism pathway. In conclusion, , as the key bacteria in donor feces, alleviate colitis in mice. The mechanism may involve increasing lecithin and regulating IL-10 production of intestinal Tregs. We demonstrate that donors with high abundance of and ameliorate dextran sulfate sodium (DSS)-induced colitis in mice by fecal microbiota transplantation (FMT). The combination therapy of and is superior to mono-bacterial therapy in ameliorating colitis in mice, of which mechanism may involve promoting lecithin and inducing IL-10 production of intestinal Tregs.