Influence of Dietary Supplementation of Probiotic Pediococcus acidilactici MA18/5M During the Transition From Freshwater to Seawater on Intestinal Health and Microbiota of Atlantic Salmon (Salmo salar L.)

Abstract

The aim of this study was to assess the effect of the transfer from freshwater to seawater on the distal intestinal bacterial communities of Atlantic salmon (Salmo salar L.) and to evaluate the effect of dietary inclusion of Pediococcus acidilactici MA18/5M (at 1.19 × 106 CFU/g). In this context, fish health and antiviral response were also investigated. A 12-week feeding trial was conducted in a flow-through rearing system involving 6 weeks in freshwater and 6 weeks in seawater. Fish received a control and probiotic diet. The composition of the salmon gut bacterial communities was determined by high-throughput sequencing of digesta and mucosa samples from both the freshwater and seawater stage. The main phyla detected during both freshwater and seawater stages were Firmicutes, Proteobacteria, Fusobacteria, and Actinobacteria. Significant differences were observed between the intestinal microbiota in the digesta and the mucosa. Both probiotic supplementation and the seawater transfer (SWT) had a substantial impact on the microbial communities, with most pronounced changes detected in the mucosal communities after SWT. This last finding together with a significantly higher antiviral response (mx-1 and tlr3 gene expression) in the distal intestine of fish fed the probiotic diet suggest a causal link between the microbiota modulation and activation of antiviral response. Feeding probiotics during the freshwater stage did not significantly increase survival after infectious pancreatic necrosis virus (IPNV) challenge after SWT, although higher survival was observed in one out of two replicate challenge tanks. In conclusion, this study demonstrated that both dietary probiotic supplementation and transfer from freshwater to seawater have an important role in modulating the bacterial communities in the distal intestine of Atlantic salmon. Furthermore, supplementation of the diet with P. acidilactici MA18/5M can modulate antiviral response.

Differential Response of Digesta- and Mucosa-Associated Intestinal Microbiota to Dietary Black Soldier Fly (Hermetia illucens) Larvae Meal in Seawater Phase Atlantic Salmon (Salmo salar)

“…Our results corroborate previous findings in rainbow trout revealing that mucosa-associated intestinal microbiota was less influenced by dietary inclusion of 30% black soldier fly larvae meal compared to digesta-associated intestinal microbiota (28,29). Results from molecular-based studies on salmonid intestinal microbiota hitherto suggest that diet modulates digesta-and mucosa-associated intestinal microbiota to varying degrees with the latter generally being more resilient to dietary interventions (19,(26)(27)(28)(29)35). As such, current practices of profiling only one of or a mixture of digesta-and mucosa-associated microbiota may obscure the response of intestinal microbiota to dietary changes.…”

“…Though Spirochaetes has typically been found in low abundances in the Atlantic salmon intestine (19,23,27,39), two recent studies have identified B. andersonii as a core taxon of both digesta-and mucosa-associated intestinal microbiota in seawater phase Atlantic salmon (35,36). Furthermore, B. andersonii is also a predominant taxon in the digesta and mucosa in one of the studies (36).…”

“…While studies in mammals and fish have revealed substantial differences between the digesta-and mucosa-associated intestinal microbiota (19,(22)(23)(24)(25), most studies investigating diet effects on the intestinal microbiota of fish have sampled the digesta only or a mixture of digesta and mucosa. Evidence is accumulating that digesta-and mucosa-associated intestinal microbiota in fish respond differently to dietary changes (19,(26)(27)(28)(29). Profiling only one of or a mixture of digestaand mucosa-associated microbiota may obscure the response of intestinal microbiota to dietary changes.…”

Differential response of digesta- and mucosa-associated intestinal microbiota to dietary black soldier fly (Hermetia illucens) larvae meal in seawater phase Atlantic salmon (Salmo salar)

“…Though Spirochaetes has typically been found in low abundances in the Atlantic salmon intestine [21,25,29,41,50], two recent studies have identified B. andersonii as a core taxon of both digesta-and mucosa-associated intestinal microbiota in seawater phase Atlantic salmon [37,38]. Notably, B. andersonii is also a predominant taxon in the digesta and mucosa in one of the studies [38].…”

“…While studies in mammals and fish have revealed substantial differences between the digesta-and mucosa-associated intestinal microbiota [21,[24][25][26][27], most studies investigating diet effects on the intestinal microbiota of fish have sampled the digesta only or a mixture of digesta and mucosa. Evidence is accumulating that digesta-and mucosa-associated intestinal microbiota in fish respond differently to dietary changes [21,[28][29][30][31]. Profiling only one of or a mixture of digestaand mucosa-associated microbiota may obscure the response of intestinal microbiota to dietary changes.…”