Having a gut feeling? Diet influences fish microbiomes and the immune system

Nutrients have diverse effects on an organism’s microbiome, which in turn influences the host’s immune system. So far, the relationship between diet, microbiome and immune response has only been studied extensively in mammals in controlled environments. 

Therefore, Friberg et al. (2019) aimed to explore this relationship in three-spined sticklebacks combining field and laboratory observations. In wild fish, they tested for gene expression profiles in different seasons. To identify diet as the driver for microbiome and gene expression alterations, experimental fish were fed a season-specific diet (summer-like/winter-like). They then created expression profiles of genes involved in seasonal immunoregulation and performed 16S rRNA sequencing on gut and gill microbiomes. 

In wild fish, season altered bacterial community structure and gene expression. In experimental fish, summer-biased genes were up-regulated during the summer-like diet and vice versa. Moreover, diet significantly influenced gut and gill microbiome compositions, with the latter being more strongly associated with immunoregulation. Particularly, they reported increased presence of pathogenic Corynebacteriales under the summer-like conditions. 

The study stresses the effect of diet on microbiome composition and immunophenotype in wild and experimental fish, whilst also addressing the issue of making inferences about mechanisms in the natural environment based on results from controlled experimental conditions. 

Friberg, I. M., Taylor, J. D., & Jackson, J. A. (2019). Diet in the Driving Seat: Natural Diet-Immunity-Microbiome Interactions in Wild Fish. Frontiers in Immunology, 10, 243. https://doi.org/10.3389/fimmu.2019.00243