Background The gut-skin axis encapsulates the concept indicating that dysbiosis in gut microbiota is associated with immune-related cutaneous diseases. Several studies have profiled the gut microbiota among psoriasis patients compared to healthy controls. However, the magnitude, direction, and most importantly, the in-depth compositional and functional profiles associated with the disease-related gut microbiota were still limited.

Objectives To explore the taxonomic and functional characteristics of gut microbiota among psoriasis patients based on metagenomics.

Methods In this study, we collected fecal samples from a cohort of 70 psoriasis patients and 25 age-, gender-matched healthy controls and explored their gut microbiota using metagenomic sequencing.

Results We observed significant alternations in the compositions of the gut microbiota of the psoriasis patients as compared to healthy controls. However, the effect sizes of both alpha diversity (a 12.3% reduction of bacterial species counts but similar evenness in psoriasis patients) and beta diversity measurements (psoriasis disease status accounts for 3.5% of total variations) are small. Among the altered bacterial species, we have observed consistent signals of Eubacterium rectale, which were greatly depleted in psoriasis patients. Intriguingly, when comparing plaque psoriasis with psoriatic arthritis patients, Eubacterium. rectale was further depleted in PSA patients. In addition, two Alisitipes species, A. finegoldii and A. shahii were also depleted in the disease cohort. Eubacterium. rectale and the two Alistipes species appeared to all contribute to the pathways of carbohydrate metabolism. These microbiomes mainly played crucial roles in producing short-chain fatty acids (SCFAs), characterized by anti-inflammatory and immunomodulation effects.

Conclusions Overall, our observations supplemented the profiling of altered gut microbiota in psoriasis at the species level and described a link between the dominated SCFAs-producing bacterial species and systemic immunity in psoriasis patients.