Background Recent research has indicated that chronic psychological stress can lead to alterations in the gut microbial community. While the involvement of gut microbiota in regulating numerous aspects of human health is well-established, their potential role in promoting cancer metastasis under chronic psychological stress and the relationship between psychological stress and microbiota remains largely unexplored.

Methods Firstly, we discovered the correlation between chronic stress and metastasis from our colorectal cancer (CRC) cohorts. We used the breast cancer (BC) metastasis model (spontaneous metastasis) and colorectal cancer metastasis model (tail-vain injection) to prove that chronic stress promoted metastasis. Additionally, germ-free animal and fecal microbiota transplantation (FMT) experiments demonstrated the involvement of microbiota. Key bacteria were then screened through 16S rRNA gene sequencing. Hormone screening and mass spectrometry were employed to clarify hormone-epithelial interplay, identifying key metabolites leading to microbiota alterations. Metabolome, whole-genome sequencing and gene editing were conducted to identify key metabolites affecting metastasis and explore mechanisms by which these bacteria resist tumor metastasis.

Results CRC patients with chronic stress exhibited enhanced metastasis compared to those without chronic stress, accompanied by altered gut microbiota, particularly a decrease in Bifidobacterium. In both CRC and BC metastasis models, mice that underwent chronic stress showed enhanced metastasis, concomitant with reduced abundance of Bifidobacterium. In germ-free mice, this promotion disappeared. However, after FMT of stress-related microbiota, mice exhibited increased metastasis. Replenishing Bifidobacterium effectively counteracted the pro-metastatic effects. Glucocorticoids notably increase post-stress, and intraperitoneal injection of glucocorticoids significantly decreases the abundance of Bifidobacterium. The metabolome of intestinal epithelial cells showed decreased guanine concentration under chronic stress, which caused the reduction of Bifidobacterium. Furthermore, analysis of the fecal metabolome of stressed mice revealed increased oleic acid, which could be degraded by oleate hydratase encoded by Bifidobacterium. Bifidobacterium or BL21 carrying oleate hydratase effectively countered tumor metastasis. Finally, our clinical data established a significantly decreased Bifidobacterium and increased oleic acid level in metastasis CRC patients.

Conclusions Chronic stress elevates glucocorticoids, reduces luminal guanine, and inhibits the growth of Bifidobacterium. This diminished capacity of Bifidobacterium to degrade oleic acid results in increased serum oleic acid levels, promoting tumor metastasis.