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Background: Association studies have linked microbiome alterations with colorectal cancer (CRC). However, differences in tumor, para-cancerous, normal mucosal, and fecal microbiota remain to be strengthened.Methods: We performed a study on the ecologically rich and taxonomically diverse of gut microbiota using three types of colorectal mucosa (tumor mucosa, para-cancerous mucosa, normal mucosa) and feces from 98 CRC patients. Additionally, we profiled the microbiota in the fecal occult blood test (FOBT) positive and negative groups at different sampling sites.Results: We found striking variations between tumor mucosal microbiota and normal mucosal microbiota. However, there was no significant difference between tumor and para-cancerous mucosal microbiota, as well as between para-cancerous and normal mucosal microbiota, revealing that the para-cancerous mucosal microbiota was a transitional state between the tumor and normal mucosal microbiota. And the substantial shifts in the fecal microbiota compared to mucosal microbiota indicated the risk of using fecal microbiota to define mucosal microbiota. A strong correlation between FOBT positive and Fusobacterium was discovered, indicating this adherent-invasive genus was closely related to intestinal bleeding. Furthermore, we identified six key genera, including Fusobacterium, Gemella, Campylobacter, Peptostreptococcus, Alloprevotella, and Parvimonas, which appear to be consistently over-represented in tumor mucosa compared to normal mucosa and/or in mucosa compared to feces.Conclusion: Compositional alterations in the microbiota existed in three types of colorectal mucosa and feces in CRC patients. Six key genera may contribute to the topographic variances in the microbiota of tumor-bearing colorectum.

Colorectal cancer (CRC) is one of the most common malignancies globally. Increasing evidence indicates that circular RNAs (circRNAs) play a pivotal role in various cancers. The present study focused on exploring the role of a functionally unknown circRNA, hsa_circ_0062682 (circ_0062682), in CRC. By online analyses and experimental validations, we showed that circ_0062682 expression was aberrantly increased in CRC tissues compared with paired normal tissues. Increased expression of circ_0062682 in CRC notably correlated with a poor prognosis and advanced tumor stage. Functional experiments showed that circ_0062682 knockdown reduced CRC growth both in vitro and in vivo. Mechanistically, we revealed that circ_0062682 could sponge miR-940 and identified D-3-phosphoglycerate dehydrogenase (PHGDH), a key oxidoreductase involved in serine biosynthesis, as a novel target of miR-940. Silencing miR-940 expression could mimic the inhibitory effect of circ_0062682 knockdown on CRC proliferation. The expression of PHGDH was downregulated in circ_0062682-depleted or miR-940 overexpressing CRC cells at both the mRNA and protein levels. Circ_0062682 knockdown suppressed CRC growth by decreasing PHGDH expression and serine production via miR-940. Taken together, these data demonstrate, for the first time, that circ_0062682 promotes serine metabolism and tumor growth in CRC by regulating the miR-940/PHGDH axis, suggesting circ_0062682 as a potential novel therapeutic target for CRC.