Macroalga-derived oligosaccharide can modify the intestinal mucus-associated bacteria of atlantic salmon

Oligosaccharides are indigestible oligomeric carbohydrates that can shape the intestinal microbiota composition. In this study, we have examined the ability of a macroalga-derived oligosaccharide to change the structure of the intestinal bacterial community of Atlantic salmon (Salmo salar). To understand this, the fish were offered feeds containing two inclusion levels (0.5% and 2.5%, LOA and HOA) of an oligo alginate (a purified potential prebiotic) for 63 days. The bacterial community of these fish was compared with that of a control group of fish, which received feeds without the additive. At the end of the feeding trial, digesta and mucus from the distal intestine were collected, and 16S rRNA sequencing was performed on an Illumina platform to determine the bacterial communities. In the case of the digesta samples, species richness, and the effective number of common and dominant species of the bacterial community of fish that consumed HOA were significantly lower compared to the control group. The community in the HOA-fed group had bacteria of closely-related lineages compared to the other fish groups. Beta diversity based on weighted UniFrac indicated the differences between the oligosaccharide-fed groups and the control group. The significantly different operational taxonomic units (OTUs) belonged to Proteobacteria, Spirochaetes, Bacteroidetes and Firmicutes. Treatment-related characteristic OTUs included those of Hyphomonas, Arenicella and Acetanaerobacterium. As for the mucus samples, the observations for the differences in alpha- and beta-diversity indices were similar to that of the digesta samples. However, 276 significantly abundant OTUs were detected in mucus, and they belonged to Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Parcubacteria, Proteobacteria, and Spirochaetes. Treatment-related characteristic OTUs belonged to Lewinella, Neorhizobium, Undibacterium and Shewanella. Thus, the macroalga-derived prebiotic altered the intestinal microbiota of Atlantic salmon. Furthermore, the oligosaccharide had a significant impact on the mucus-associated bacteria, and this characteristic could be exploited for maintaining intestinal health of farmed fish.