show Abstracthide AbstractSegatella copri is a prevalent member of the human gut microbiota that has been associated with both health and disease states. How it adapts to the changing conditions in the gut to achieve effective colonization remains to be understood. By mapping the primary transcriptome of S. copri and examining human-derived samples , we uncover an important regulator of gut colonization in S. copri, a small RNA named here Segatella RNA colonization factor (SrcF). Deletion of SrcF rendered S. copri unable to colonize the gut in a gnotobiotic mouse model. SrcF regulates genes involved in nutrient acquisition, and its expression is in turn controlled by complex carbohydrates, particularly fructans. Human microbiome composition and breakdown of fructans by cohabitating commensals impact SrcF expression, suggesting that complex carbohydrate breakdown beyond contributing energy sources also mediates inter-species signaling among commensals. Together, this study highlights the contribution of non-coding sRNAs as key regulators for gut colonization.