Probiotic consumption relieved human stress and anxiety symptoms possibly via modulating the neuroactive potential of the gut microbiota

Stress has been shown to disturb the balance of human intestinal microbiota and subsequently causes mental health problems like anxiety and depression. Our previous study showed that ingesting the probiotic strain, Lactobacillus (L.) plantarum P-8, for 12 weeks could alleviate stress and anxiety of stressed adults. The current study was a follow-up work aiming to investigate the functional role of the gut metagenomes in the observed beneficial effects. The fecal metagenomes of the probiotic (n = 43) and placebo (n = 36) receivers were analyzed in depth. The gut microbiomes of the placebo group at weeks 0 and 12 showed a significantly greater Aitchison distance (P < 0.001) compared with the probiotic group. Meanwhile, the Shannon diversity index of the placebo group (P < 0.05) but not the probiotic group decreased significantly at week 12. Additionally, significantly more species-level genome bins (SGBs) of Bifidobacterium adolescentis, Bifidobacterium longum, and Fecalibacterium prausnitzii (P < 0.01) were identified in the fecal metagenomes of the probiotic group, while the abundances of SGBs representing the species Roseburia faecis and Fusicatenibacter saccharivorans decreased significantly (P < 0.05). Furthermore, the 12-week probiotic supplementation enhanced the diversity of neurotransmitter-synthesizing/consuming SGBs and the levels of some predicted microbial neuroactive metabolites (e.g., short-chain fatty acids, gamma-aminobutyric acid, arachidonic acid, and sphingomyelin). Our results showed a potential link between probiotic-induced gut microbiota modulation and stress/anxiety alleviation in stressed adults, supporting that the gut-brain axis was involved in relieving stress-related symptoms. The beneficial effect relied not only on microbial diversity changes but more importantly gut metagenome modulations at the SGB and functional gene levels.