Unraveling the Relationship Between the Gut Microbiome and Colorectal Cancer: Insights from 16S rRNA Gene Sequencing

Colorectal cancer is becoming acknowledged as a condition influenced by the interplay between host factors and gut bacteria. This study examines microbiome changes linked to colorectal cancer (CRC) and their distribution throughout tumor tissue, adjacent mucosa and peripheral blood by 16S rRNA gene sequencing. Two complementary datasets were examined: a case-control analysis comparing colorectal cancer (CRC) to noninvasive colon biopsies and a paired multi-site cohort comprising tumor samples, matched healthy tissues, and blood from the same individual. Samples were processed using a standard approach that included ASV inference and community analysis based on QIIME2. Alpha diversity did not exhibit a substantial decrease in CRC tissues relative to controls while beta diversity demonstrated major compositional changes. Differential abundance analysis showed that CRC-associated taxa, especially Fusobacterium nucleatum and Parvimonas micra, were more common. While butyrate-producing commensals such Faecalibacterium and Roseburia were less common. Comparisons between patients showed compartment-specific patterns. The tumor and surrounding mucosa largely overlapped, while the blood showed a distinct low-biomass signature that was carefully interpreted as indicating signals from circulating bacterial DNA. The data indicate the presence of stable, site-specific microbial alterations in CRC, rather than a uniform decline in diversity while causal relationships cannot be established. The identified patterns align with mechanisms of inflammation, immunological regulation and metabolic disruption. Multi-compartment microbiome profiling may enhance biological comprehension and facilitate the future advancement of microbiota-informed diagnostic and treatment approaches in colorectal cancer.