Gracilaria gracilis and Nannochloropsis oceanica, singly or in combination, in diets alter the intestinal microbiota of European seabass (Dicentrarchus labrax)

Abstract

Algae feeds and fish gut microbiota have been given importance in the past few years because of the necessity to rely on sustainable ingredients in aquafeeds and the link of host-associated microbes to organismal health. But little is known about the potential of algae, particularly of micro- and macroalgae combination, to shape the intestinal bacterial communities. Hence, in the present work, the 16S rRNA gene sequencing technique was employed to unravel the effects of the seaweed Gracilaria gracilis and the microalga Nannochloropsis oceanica - included either singly or in combination in the diets of European seabass - on the diversities and composition of the gut bacterial communities. Results indicated that 8% inclusion of either G. gracilis (GRA) or N. oceanica (NAN) led to a reduction in the gut microbial diversity. On the other hand, inclusion of the micro- and macroalga in a blend (NANGRA) mitigated these plausible effects on the intestinal bacterial communities. The core microbiota of European seabass was composed of both beneficial (Lactobacillus and Cetobacterium) and potentially pathogenic (Flavobacterium) bacteria. The GRA diet was associated with a lower abundance of carbohydrate degraders and also promoted the growth of bacteria capable of outcompeting fish pathogens (Sulfitobacter and Methylobacterium). On the other hand, the NAN diet led to a higher representation of the genus Bacillus, with probiotic potential, accompanied by a decrease in Vibrio, a genus encompassing several fish pathogenic species. These findings demonstrate the ability of micro- and macroalgae to modulate the gut microbiota of European seabass, with plausible implications to host gut homeostasis.

Skin and Blood Microbial Signatures of Sedentary and Migratory Trout (Salmo trutta) of the Kerguelen Islands

“…However, a clear difference at the phylum level was noted by the abundance of Actinomycetota and Parcubacteria in the blood microbiome, but not in the mucus, of both migratory and sedentary trout. This signature is, in fact, similar to a recent metagenomic study showing that bacteria enriched in seawater in polar regions were mostly Pseudomonadota, Actinomycetota, Bacteroidota, and Parcubacteria [50], the latter being one of the most abundant phyla in intestinal fish microbiota [57,58]. Interestingly, we also found a similar signature in the hemolymphatic (blood-like) microbiome of mussel species (Figure S10) that inhabit the coastal marine ecosystems of the Kerguelen Islands [59].…”

Seaweed and Seaweed-Based Functional Metabolites as Potential Modulators of Growth, Immune and Antioxidant Responses, and Gut Microbiota in Fish

“…On the contrary, a high inclusion (8%) of G. gracilis resulted in a significant reduction of gut microbial diversity. However, these negative impacts were mitigated at a lower inclusion level (4%) [197]. Tapia-paniagua et al [198] reported that a relatively low (<3%) dietary administration of Ulva ohnoi significantly enhanced the diversity of whole gut microbes in Senegalese sole (Solea senegalensis), while 5% U. ohnoi did not exhibit a significant influence on gut microbial diversity [196].…”

“…Seaweed has been shown to be a promising feed additive that can modulate the gut microbial composition of fish [196]. The dietary inclusion of Gracilaria gracilis enhanced the abundance of the microbes Sulfitobacter and Methylobacterium in the gut of European seabass [197]. These microbes are capable of producing short-and medium-chain fatty acids and can lower the pH of the intestine, thus playing a crucial role in suppressing pathogenic bacteria and potentially representing a promising method of enhancing disease resistance in fish [213,214].…”

An in-depth characterisation of European seabass intestinal segments for assessing the impact of an algae-based functional diet on intestinal health

“…This analysis reported that the anterior and mid sections are mostly associated with feed digestion and nutrient absorption, whereas the posterior/rectal segments are especially relevant for immune functions 26 . The posterior/rectal regions are also the preferred sections for understanding the diet-induced modulation of the microbial communities 27 – 30 . Nonetheless, the lack of a comprehensive study of the morphology and physiology of seabass intestine hampers the ability to selectively modulate specific targeted traits and hence contribute to precision nutrition.…”