Animal by-product meals from the rendering industry could provide a sustainable and commercially viable alternative to fishmeal (FM) in aquaculture, as they are rich in most essential amino acids and contain important amounts of water-soluble proteins that improve feed digestibility and palatability. Among them, poultry by-product meal (PBM) have given encouraging results in rainbow trout (Oncorhynchus mykiss). However, the introduction of new ingredients in the diet needs to be carefully evaluated since diet is one of the main factors affecting the gut microbiota, which is a complex community that contributes to host metabolism, nutrition, growth, and disease resistance. Accordingly, we investigated the effects of partial replacement of dietary FM with a mix of animal by-product meals and plant proteins on intestinal microbiota composition of rainbow trout in relation to growth and feeding efficiency parameters. We used 1540 trout with an initial mean body weight of 94.6 ± 14.2 g. Fish were fed for 12 weeks with 7 different feed formulations. The growth data showed that trout fed on diets rich in animal by-product meals grew as well as fish fed on control diet, which was rich in FM (37.3%) and PBM-free. High-throughput 16S rRNA gene amplicon sequencing (MiSeq platform, Illumina) was utilised to study the gut microbial community profile. After discarding Cyanobacteria (class Chloroplast) and mitochondria reads a total of 2,701,274 of reads taxonomically classified, corresponding to a mean of 96,474 ± 68,056 reads per sample, were obtained. Five thousand three hundred ninety-nine operational taxonomic units (OTUs) were identified, which predominantly mapped to the phyla of Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria. The ratio between vegetable and animal proteins proved to play a central role in determining microbiome profiles and Firmicutes and Proteobacteria phyla were particularly discriminatory for diet type in trout. Plant ingredients favoured a higher Firmicutes:Proteobacteria ratio than animal proteins. Acceptable abundance of Firmicutes was guaranteed by including at least 25% of vegetable proteins in the diet regardless of animal protein source and percentage. In summary animal by-product meals, as replacements to FM, gave good results in terms of growth performances and did not induce significant changes in gut microbial richness, thus proving to be a suitable protein source for use in rainbow trout aqua feed.

Background This study evaluated the effects of partial substitution of dietary fishmeal (FM) with either fish protein hydrolysate (FPH) or autolysed dried yeast (HiCell®, Biorigin, Brazil) on intestinal microbiota of gilthead sea bream (Sparus aurata). A total number of 720 fish of 122.18 ± 6.22 g were fed for 92 days with three different diets in triplicate (3 tanks/diet). A diet based on FM/vegetable meal was used as control. The other two diets were formulated by replacing FM with 5% of either FPH or HiCell®. To analyze the gut microbiota associated to autochthonous and allochthonous microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and QIIME pipeline were used. Results A total number of 102 OTUs (operational taxonomic units) at 97% identity were identified in fish gut samples collected at the end of feeding trial. Fourteen OTUs constituted the core gut microbiota, i.e. those OTUs found in at least nine out of fifteen samples per group and shared regardless of the diet. Eight OTUs were assigned to Firmicutes represented by Lactobacillus, Staphylococcus, and Bacillus genera, and six to Proteobacteria phylum. Dietary dried yeast autolysate modulated the intestinal microbiota by promoting the growth of some beneficial bacteria. At order level, fish fed yeast showed an enrichment in Bacillales and Clostridiales as compared to the control group, whereas fish fed FPH showed a significantly lower amount of bacteria belonging to Alteromonadales and Enterobacteriales than the other two feeding groups. Although we did not observe any effect of 5% FM replacement with alternative nitrogen sources at phylum level, at lower taxonomical levels, the composition of gut microbiota, in terms of relative abundance of specific taxa, was significantly influenced by the dietary treatment. Conclusions The metabarcoding analysis revealed a clearly intestinal microbiota modulation in response to dietary autolyzed yeast. The abundance of some beneficial bacteria, i.e. indigestible carbohydrate degrading- and SCFA producing bacteria, was positively affected. Brewer’s yeast autolysate could be a valid alternative protein source to FM as well as a valid functional ingredient for aquafeed production.

Host responses to infectious and inflammatory stimuli are altered with aging. Because cytokines and their antagonists are significant factors in these host responses, the present research on aged subjects was designed to investigate plasma concentrations of the cytokines interleukin 1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) and those of their antagonists IL-1 receptor antagonist (IL-1ra) and soluble TNF receptor (sTNFr). For this research, 122 apparently healthy aged subjects (79.6 +/- 5.8 yr), 39 aged individuals with documented urinary tract infections (UTIs) (81.6 +/- 6.3 yr), and 100 young controls (39.32 +/- 11.2 yr) were included. Plasma IL-1 beta, TNF alpha, IL-1ra, sTNFr (55 kDa), and neopterin were measured using enzyme-linked immunosorbent assay techniques. In subsets of normal aged subjects and UTI patients, we investigated relations between plasma concentrations of cytokine antagonists and IL-2 production by phytohemagglutinin-stimulated peripheral blood mononuclear cells. The results show that plasma concentrations of both IL-1ra and sTNFr were greater in healthy aged subjects than in young controls. Plasma neopterin, a product of activated monocytes/macrophages, was likewise elevated in the aged. IL-1 and TNF were not detectable in the majority of plasma samples. There was a positive correlation between neopterin concentration and both IL-1ra and sTNFr. There was a significant negative correlation between plasma IL-1ra and IL-2 production by phytohemagglutinin-stimulated peripheral blood mononuclear cell in healthy aged subjects. IL-1ra and sTNFr concentrations were significantly greater in patients with UTI than in the healthy aged subjects. In UTI patients IL-2 production in vitro was lower than in healthy subjects, but there was no significant correlation with IL-1ra in plasma. Therefore, plasma concentrations of cytokine antagonists are increased in plasma of apparently healthy aged subjects. Elevated concentrations of neopterin suggest that this increase can be traced to monocyte activation. The negative correlation between plasma IL-1ra and IL-2 production in vitro suggests that enhancement of this cytokine antagonist can contribute to immunodepression of aging. We propose that unapparent infections in aged subjects cause monocyte activation and release of cytokine antagonists. These cytokine antagonists reduce IL-2 production and the capability of T cells to proliferate, thereby inhibiting responses in the elderly.

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