Modulation of gut microbiota and intestinal immune response in gilthead seabream (Sparus aurata) by dietary bile salt supplementation

Abstract

Given their role in lipid digestion, feed supplementation with bile salts could be an economic and sustainable solution to alterations in adiposity and intestinal inflammation generated by some strategies currently used in aquaculture. An important part of the metabolism of bile salts takes place in the intestine, where the microbiota transforms them into more toxic forms. Consequently, we aimed to evaluate the gut immune response and microbial populations in gilthead seabream (Sparus aurata) fed a diet supplemented with a blend of bile salts with proven background as a regulator of lipid metabolism and fat content. After the 90-day feeding trial, a differential modulation of the microbiota between the anterior and posterior intestine was observed. While in the anterior intestine the relative abundance of Desulfobacterota doubled, in the posterior intestine, the levels of Firmicutes increased and Proteobacteria, Actinobacteriota, and Campylobacterota were reduced when supplementing the diet with bile salts. Even so, only in the anterior intestine, there was a decrease in estimated richness (Chao1 and ACE indices) in presence of dietary bile salts. No significant differences were displayed in alpha (Shannon and Simpson indices) nor beta-diversity, showing that bile sales did not have a great impact on the intestinal microbiota. Regarding the gene expression profile in 2 h postprandial-fish, several changes were observed in the analyzed biomarkers of epithelial integrity, nutrient transport, mucus production, interleukins, cell markers, immunoglobulin production and pathogen recognition receptors. These results may indicate the development of an intestinal immune-protective status to tackle future threats. This work also suggests that this immune response is not only regulated by the presence of the dietary bile salts in the intestine, but also by the microbial populations that are in turn modulated by bile salts. After a fasting period of 2 days, the overall gene expression profile was stabilized with respect to fish fed the unsupplemented diet, indicating that the effect of bile salts was transient after short periods of fasting. On the balance, bile salts can be used as a dietary supplement to enhance S. aurata farming and production without compromising their intestinal health.

The potential of a combination of pungent spices as a novel supplement in gilthead seabream (Sparus aurata) diets to aid in the strategic use of fish oil in aquafeeds: a holistic perspective

“…Regarding the gut microbial composition, several studies have highlighted that the most dominant bacterial phyla of the gut microbial communities in gilthead seabream are Firmicutes, Proteobacteria, Bacteroidota, and Actinobacteriota ( 44 , 99 ), in line with the results obtained in the present work. Under current conditions, the gut microbial community composition was very conserved, with only an increase in the relative abundance of Chloroflexi in the PI of fish fed the SPICY 0.1% diet.…”

“…Under current conditions, the gut microbial community composition was very conserved, with only an increase in the relative abundance of Chloroflexi in the PI of fish fed the SPICY 0.1% diet. This is a widespread and metabolically diverse phylum of bacteria that has been reported as part of fish microbiota ( 44 , 100 , 101 ), but whose role remains unknown. No differences were found in the values of the F/B ratio, which is a well-documented factor whose changes have been used as a biomarker of intestinal dysbiosis in fishes ( 102 ).…”

“…The region V3–V4 of the 16S rRNA gene was amplified (primers 341F/805R) and sequenced (llumina-MiSeq platform; 2 × 300 bp paired-end) according to Ruiz et al. ( 44 ), and data analysis was carried out with a workflow based on the R package dada2 (v1.16; 45 ). In brief, all reads with a Phred quality score <28 or with an expected error >2 were excluded from the analysis.…”

“…Real-time quantitative PCR was carried out with a CFX96 Connect ™ Real-Time PCR Detection System (Bio-Rad, USA), using 96-well PCR array layouts designed for simultaneously profiling a panel of 44 genes for liver ( Table 2 ) and intestine ( Table 3 ) as described by Ruiz et al. ( 44 ). To improve data reproducibility, all the pipetting operations were performed using an EpMotion 5070 Liquid Handling Robot (Eppendorf, Germany).…”

Impact of the diet in the gut microbiota after an inter-species microbial transplantation in fish

“…This was reflected in the presence of Catenococcus and Brevinema up to 16 days post-IMT, as both genera were found only in gilthead seabream from the pre-IMT group, but not in the Atlantic salmon microbiota, nor in the GSB diet. Therefore, their presence after the IMT may be associated to either environmental factors or to factors intrinsic to the fish species such as their physiology, or genetic background, as both bacterial genera have been previously reported as part of the autochthonous fish microbiota 72 – 74 . Neither of these genera were maintained in the long-term (36 days post-IMT), though it may be due to the higher impact of the GSB diet, as the abundance of Brevinema in the fish gut mucosa has been shown to be easily modulated by the ingredient composition of the diet 75 , 76 , or due to competition with other bacteria after the IMT.…”