Discovery and characterization of Christensenella hongkongensis as a novel bacterium in the adenoma-carcinoma progression

Background Colorectal cancer (CRC) is one of the most prevalent malignancies worldwide and commonly starts from a pre-cancerous stage. This study aimed to identify potential fecal bacterial candidates associated with progression of CRC from the adenoma-carcinoma sequence and to explore underlying mechanisms of carcinogenesis. Methods Publicly metagenomic datasets were analyzed using MaAsLin2 to identify bacterial species enriched in CRC patients compared to healthy controls. Additionally, we established a large cohort in mainland China, consisting of 686 subjects (285 CRC patients, 73 advanced adenoma patients, 134 non-advanced adenoma patients, and 194 healthy controls). Fecal samples from this cohort were analyzed by duplex quantitative polymerase chain reaction (qPCR) to validate the abundance of key bacterial candidate and its association with tumor node metastasis (TNM) stages. In vitro experiments and transcriptome sequencing were performed to explore the effects of Christensenella hongkongensis ( C. hongkongensis ) and its mechanisms in CRC progression. Results MaAsLin2 analysis identified seven bacterial species were significantly more abundant in fecal samples of CRC patients than in healthy controls ( P  < 0.05). Among them, Christensenella hongkongensis , an obligately anaerobic, catalase-positive, motile, non-sporulating, gram-positive coccobacillus was distinguished by its lowest abundance in healthy controls and significant enrichment in CRC patients. Validation in our recruited cohort showed that the abundance of C. hongkongensis progressively increased from non-advanced adenomas to advanced adenomas and CRC. Linear regression analysis revealed a significant positive association between C. hongkongensis and TNM stages in CRC. In vitro experiments showed that C. hongkongensis promoted CRC cell proliferation, inhibited apoptosis, and enhanced the growth of patient-derived CRC organoids. RNA-seq analysis identified activation of the Wnt/β-catenin signaling pathway, which was further validated by the upregulation of downstream targets such as c-Jun and Cyclin-D1. Conclusions Our findings suggest that C. hongkongensis promotes colorectal tumorigenesis via Wnt/β-catenin activation, and highlights its potential as a novel non-invasive bacteria marker for early detection and monitoring of CRC progression.