The gut microbiome plays a crucial role in the health and well-being of animals, including fish. Microbiome-targeted dietary interventions (MDF) have gained attention as a strategy to enhance animal production systems by promoting beneficial gut microbes.
Scientists from the Norwegian University of Life Sciences, the University of Copenhagen, the Swedish University of Agricultural Sciences, Cargill Food Solutions, Cargill Aqua Nutrition, SINTEF, and Queensland University of Technology (QUT) investigated the effects of MDF interventions on the composition and functionality of the gut microbiome in Atlantic salmon (Salmo salar).
Promising Candidates: α- and β-Mannans
Previous research has shown positive results with specific carbohydrates such as α-mannan oligosaccharides (α-MOS) in salmon feeds. These carbohydrates, derived from yeast cell walls, may potentially benefit salmon by promoting the growth of lactic acid-producing bacteria like Carnobacterium. Additionally, β-mannans, plant-based glycans found in human and livestock diets, represent another promising class of MDF. Depending on the source, β-mannans can be classified into subtypes with distinct functionalities.
Unlocking the Salmon Gut Microbiome
However, a major challenge in designing effective MDFs for salmon is the lack of comprehensive information on the salmon gut microbiome. While preliminary studies have identified specific bacterial genera like Carnobacterium, Roseburia, and Faecalibacterium, detailed understanding of their enzymatic capacities and metabolic pathways has been limited.
This research addresses this gap by using a recently developed resource called the Salmon Microbiome Genome Atlas (SMGA). The SMGA is a comprehensive collection of genetic information from cultured bacterial strains isolated from the salmon intestine. This resource allows scientists to explore the functional potential of the salmon gut microbiome and identify bacteria with specific enzymatic capacities that can be targeted with MDFs.
The Study
Researchers used a combination of metataxonomic data and prior knowledge of α-mannan oligosaccharides (MOS) and β-mannan-derived MDF to study the effects of two α-mannans and an acetylated β-galactoglucomannan on the gut microbiome of Atlantic salmon. The MDFs were added to the diet at a 0.2% dose, and researchers analyzed the effects on both host gene expression and the structure and function of the gut microbiome.
Effects of Microbiome-Targeted Dietary Interventions
Results showed that the MDFs had minimal effects on both host gene expression and the structure and function of the gut microbiome under the studied conditions. However, a subsequent trial using a higher dietary inclusion of β-mannan (4%) significantly altered the gut microbiome composition. Despite this change, there were no biologically relevant effects on salmon metabolism and physiology.
Researchers also identified a single population of Burkholderia-Caballeronia-Paraburkholderia (BCP) that showed consistent and significant abundance changes in both feeding trials. However, no evidence of β-mannan utilization capacities or gene transcription changes to produce beneficial metabolites for the host was found.
In light of these findings, the researchers revisited their omics data to predict and describe previously unreported, potentially beneficial endogenous lactic acid bacteria that should be targeted by future MDF strategies for salmon. These findings underscore the importance of further research in developing more effective MDFs to improve the health and well-being of Atlantic salmon.
Key Findings
- Minimal Impact on Gut Microbiome and Host Gene Expression: Low-dose dietary supplementation (0.2%) with the tested MDFs had negligible effects on the gut microbiome structure and function of salmon. Additionally, no significant changes in host gene expression patterns were observed.
- Limited Effects of Higher Dose Supplementation: Increasing β-mannan inclusion to 4% in the diet caused a shift in gut microbiome composition. However, these changes did not translate into any biologically relevant effects on salmon metabolism or physiology.
- A Single Bacterial Group Responds: The only consistent response to low- and high-dose fiber supplementation was observed in a specific bacterial group within the Burkholderia-Caballeronia-Paraburkholderia (BCP) genus. Despite these changes, there was no evidence that these bacteria utilized β-mannan or produced beneficial metabolites for the host.
Conclusion
Microbiome-targeted dietary interventions hold great promise for enhancing animal production systems, yet further research is needed to understand their effects on fish gut microbiomes. This study highlights the importance of additional research into developing more effective MDFs to improve the health and well-being of Atlantic salmon.
By focusing on previously unreported, potentially beneficial endogenous lactic acid bacteria, future MDF strategies may be more effective in promoting beneficial gut microbes and improving salmon health.
The study was funded by the Research Council of Norway, the Swedish Research Council Formas, and the European Union’s Horizon 2020.
Contact
Sabina Leanti La Rosa
Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
Faculty of Biosciences, Norwegian University of Life Sciences, Ås, Norway
Email: sabina.leantilarosa@nmbu.no
Reference (open access)
Gupta, S., Kodama, M., Hoetzinger, M., Clausen, C. G., Pless, L., Verissimo, A. R., Stengel, B., Calabuig, V., Kvingedal, R., Skugor, S., Westereng, B., Harvey, T. N., Nordborg, A., Bertilsson, S., Limborg, M. T., Mørkøre, T., Sandve, S. R., Pope, P. B., Hvidsten, T. R., . . . La Rosa, S. L. (2024). The need for high-resolution gut microbiome characterization to design efficient strategies for sustainable aquaculture production. Communications Biology, 7(1), 1-10. https://doi.org/10.1038/s42003-024-07087-4
