SRP320947 PRJNA732058 Interaction between endometrial microbiota and host gene regulation in recurrent implantation failure Recurrent implantation failure (RIF) had become a new major challenge for assisted reproductive technology. In this study, we characterized the interaction between the host and microbiota based on the endometrial transcriptome and microbiota. Based on 16s rRNA gene sequencing of the endometrium, the species diversity of the microbiota of RIF patients was higher than that of the CON group (p < 0.001). The most abundant bacteria in the endometrium changed from Lactobacillus (CON group) to Sphingomonas (RIF group). Younger patients had higher Corynebacterium_1 abundance than elderly patients. Combined with the expression data of endometrial receptivity genes, we found that Sphingomonas mainly reduced the receptivity of the endometrium by affecting the formation of blood vessels in the endometrium. And PICRUST2 results showed the endometrial microbiota of RIF patients might be more sensitive to beta-lactam antibiotics. For the first time, this study illustrated the interaction mechanism between the host and microbiota in the endometrium of patients with RIF.