Abstract
A healthy gastrointestinal microbiota is essential for host fitness, and strongly modulated by host diet. In aquaculture, a current challenge is to feed carnivorous fish with plant-feedstuffs in substitution of fish meal, an unsustainable commodity. Plants have a limited nutritive value due to the presence of non-starch polysaccharides (NSP) which are not metabolized by fish. In this work we assessed the effects of NSP-enriched diets on European seabass gut microbiota and evaluate the selective pressure of plant feedstuffs towards gut microbes with NSP-hydrolytic potential, i.e. capable to convert indigestible dietary constituents in fish metabolites. Triplicate groups of European seabass juveniles were fed a fish meal-based diet (control) or three plant-based diets (SBM, soybean meal; RSM, rapeseed meal; SFM, sunflower meal) for 6 weeks, before recovering intestinal samples for microbiota analysis, using the Illumina’s MiSeq platform. Plant-based diets impacted differently digesta and mucosal microbiota. A decrease (p = 0.020) on species richness, accompanied by a decline on the relative abundance of specific phyla such as Acidobacteria (p = 0.030), was observed in digesta samples of SBM and RSM experimental fish, but no effects were seen in mucosa-associated microbiota. Plant-based diets favored the Firmicutes (p = 0.01), in particular the Bacillaceae (p = 0.017) and Clostridiaceae (p = 0.007), two bacterial families known to harbor carbohydrate active enzymes and thus putatively more prone to grow in high NSP environments. Overall, bacterial gut communities of European seabass respond to plant-feedstuffs with adjustments in the presence of transient microorganisms (allochthonous) with carbohydrolytic potential, while maintaining a balanced core (autochthonous) microbiota.
Highlights
The gastrointestinal tract is one of the most crowded bacterial communities on earth
The dietary inclusion of SBM, SFM, or RSM had no effect on European seabass growth performance, feed intake, feed efficiency, protein efficiency ratio and N intake (Table 1)
Taxa showing a mean proportion of 1% or higher in any experimental feeding condition (CTR, SBM, RSM & SFM) or intestinal sample (Digesta & Mucosa) were considered as the most abundant
Summary
The gastrointestinal tract is one of the most crowded bacterial communities on earth. Diet has a tremendous influence on gut-microbiota composition and e quilibrium[22,23,24,25,26] This is important in animal nutrition and production, where industry trends dictate a continuous evolution of raw materials, feedstuffs, and supplements used to feed farmed animals[27,28]. Here we analyze, through 16S rRNA amplicon sequencing, the dynamics of gut microbiota of European seabass juveniles fed the same challenging plant-based diets to elucidate putative selective pressures favoring a gut microbiota more fit to metabolize nonstarch polysaccharides. This knowledge might contribute to identify new probiotics and improve aquaculture practices of carnivorous fish fed with plant-based diets
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