Alginate oligosaccharide-induced shift in the intestinal microbiota of salmon.

Prebiotics are food/feed additives intended to sculpt gut microbial communities as they are selectively utilized by the microorganisms to exert beneficial health effects on hosts. Macroalga-derived oligosaccharides are potential prebiotics, and herein, we determined the effects of Laminaria sp.-derived alginate oligosaccharide (AlgOS) on the distal intestinal microbiota of Atlantic salmon (Salmo salar). Using a high-throughput 16S rRNA gene amplicon sequencing technique, we investigated the microbiota harboured in the intestinal content and mucus of Atlantic salmon offered feeds supplemented with 0.5 and 2.5% AlgOS. We found that AlgOS shifts the intestinal microbiota profile; alpha diversity was significantly reduced with 2.5% AlgOS while with 0.5% AlgOS the alteration occurred without impacting the bacterial diversity. Beta diversity showed a significant difference between control and AlgOS-fed groups. AlgOS supplementation facilitated the dominance of Proteobacteria and Spirochaetes, promoting the growth of presumed butyrate producers in the intestine. In addition, 0.5% AlgOS stimulated certain bacteria belonging to Proteobacteria, Spirochaetes and Actinobacteria. This indicates that the low inclusion of AlgOS can plausibly induce a prebiotic effect on the distal intestinal microbiota of Atlantic salmon. These results are expected to generate further interest in the potential of macroalgae-derived oligosaccharides as prebiotics for food and feed applications.