Prebiotics modify host metabolism in rainbow trout (Oncorhynchus mykiss) fed with a total plant-based diet: Potential implications for microbiome-mediated diet optimization

Exploring the effects of dietary inulin in rainbow trout fed a high-starch, 100% plant-based diet

BACKGROUND

High dietary carbohydrates can spare protein in rainbow trout (Oncorhynchus mykiss) but may affect growth and health. Inulin, a prebiotic, could have nutritional and metabolic effects, along with anti-inflammatory properties in teleosts, improving growth and welfare. We tested this hypothesis in rainbow trout by feeding them a 100% plant-based diet, which is a viable alternative to fishmeal and fish oil in aquaculture feeds. In a two-factor design, we examined the impact of inulin (2%) as well as the variation in the carbohydrates (CHO)/plant protein ratio on rainbow trout. We assessed the influence of these factors on zootechnical parameters, plasma metabolites, gut microbiota, production of short-chain fatty acids and lactic acid, as well as the expression of free-fatty acid receptor genes in the mid-intestine, intermediary liver metabolism, and immune markers in a 12-week feeding trial.

RESULTS

The use of 2% inulin did not significantly change the fish intestinal microbiota, but interestingly, the high CHO/protein ratio group showed a change in intestinal microbiota and in particular the beta diversity, with 21 bacterial genera affected, including Ralstonia, Bacillus, and 11 lactic-acid producing bacteria. There were higher levels of butyric, and valeric acid in groups fed with high CHO/protein diet but not with inulin. The high CHO/protein group showed a decrease in the expression of pro-inflammatory cytokines (il1b, il8, and tnfa) in liver and a lower expression of the genes coding for tight-junction proteins in mid-intestine (tjp1a and tjp3). However, the 2% inulin did not modify the expression of plasma immune markers. Finally, inulin induced a negative effect on rainbow trout growth performance irrespective of the dietary carbohydrates.

CONCLUSIONS

With a 100% plant-based diet, inclusion of high levels of carbohydrates could be a promising way for fish nutrition in aquaculture through a protein sparing effect whereas the supplementation of 2% inulin does not appear to improve the use of CHO when combined with a 100% plant-based diet.

Rapid adaptation of the rainbow trout intestinal microbiota to the use of a high-starch 100% plant-based diet

Short-term adaptation of the microbiota could promote nutrient degradation and the host health. While numerous studies are currently undertaking feeding trials using sustainable diets for the aquaculture industry, the extent to which the microbiota adapts to these novel diets is poorly described. The incorporation of carbohydrates (CHO) within a 100% plant-based diet could offer a novel, cost-effective energy source that is readily available, potentially replacing the protein component in the diets. In this study, we investigated the short-term (3 weeks) effects of a high CHO, 100% plant-based diet on the mucosal and digesta associated microbiota diversity and composition, as well as several metabolic parameters in rainbow trout. We highlighted that the mucosa is dominated by Mycoplasma (44.86%). While the diets did not have significant effects on the main phyla (Proteobacteria, Firmicutes, and Actinobacteria), after 3 weeks, a lower abundance of Bacillus genus, and higher abundances of four lactic-acid bacteria were demonstrated in digesta. In addition, no post-prandial hyperglycemia was observed with high carbohydrate intake. These results provide evidence for the rapid adaptation of the gut microbiota and host metabolism to high CHO in combination with 100% plant ingredients in rainbow trout.

Interaction between genetics and inulin affects host metabolism in rainbow trout fed a sustainable all plant-based diet

Inulin affects nutrition and metabolism in many animals. Although inulin is widely used in the diet of teleosts, its mechanism of action is unknown. Here, we investigated the effect of inulin (2 %) on the intestinal microbiome and metabolism in rainbow trout (Oncorhynchus mykiss) selected for growth and survival when fed a 100 % plant-based diet (suave) and a control line (temoin). Metabolic responses to the two factors (line and inulin) in liver, intestine, muscle and adipose were tissue-specific, with line and interaction between the two factors influencing overall expression in liver. In the intestine, inulin and line and in muscle, line influenced the expression of metabolic genes. Microbiota between the mucus and digestive contents was significantly different, with genera from Proteobacteria being more abundant in the mucus, whereas genera from the Firmicutes and Planctomycetes being more abundant in contents. Effect of inulin and interaction between factors on the microbiome was evident in contents. The significant taxa of control and inulin-fed groups differed greatly with Streptococcus and Weissella being significantly abundant in the inulin-fed group. There was a general trend showing higher levels of all SCFA in temoin group with propionic acid levels being significantly higher. An operational taxonomic unit (OTU) belonging to the Ruminococcaceae was significantly abundant in suave. The tissue-specific correlations between OTU and gene expression may indicate the link between microbiome and metabolism. Together, these results suggest that line and inulin impact the gene expression in a tissue-specific manner, possibly driven by specific OTUs enriched in inulin-fed groups and suave.

Rainbow trout (Oncorhynchus mykiss) physiological response to microplastics and enrofloxacin: Novel pathways to investigate microplastic synergistic effects on pharmaceuticals

Enrofloxacin (ENR) is a broad-spectrum antibiotic widely used due to its efficacy against pathogens. Microplastics (MPs) may bind to ENR and reduce its efficiency, whereas there would be an increase in its toxicity, bioavailability, and bio-accumulation rates. Therefore, the hypothesis is that the interaction between MPs and ENR can alter their toxicity and bioavailability. The subjective of this study is to examine the toxicity of various concentrations of ENR (0, 1.35, and 2.7 ml Kg^-1 diet) and MPs (0, 1000, and 2000 mg Kg^-1 diet) alone and in combination for 21 days. The rainbow trout (Oncorhynchus mykiss) is an economic aquaculture species used as an experimental model in ecotoxicology studies. Blood biochemical analytes indicated that ENR and MPs combination led to increasing enzymatic activity of each biomarker, except for gamma-glutamyl-transferase (GGT). Alterations related to triglycerides, cholesterol, glucose, urea, creatinine, total protein, and albumin blood contents were observed. An elevation in the levels of superoxide dismutase (SOD), malondialdehyde (MDA), and glucose 6-phosphate dehydrogenase (G6PDH) was found in the liver. In contrast, catalase (CAT) and glutathione peroxidase (GPx) levels decreased. Furthermore, a decline was observed in the cellular total antioxidant (ANT) levels. These findings suggested that ENR and MPs could affect fish health both independently and together. Consequently, the study determined that when both ENR and MPs were present in high concentrations, the toxicity of ENR was amplified, providing further evidence of the synergistic impact of MPs on ENR toxicity.

Preparation and Evaluation of a Dosage Form for Individualized Administration of Lyophilized Probiotics

Probiotics have been used in human and veterinary medicine to increase resistance to pathogens and provide protection against external impacts for many years. Pathogens are often transmitted to humans through animal product consumption. Therefore, it is assumed that probiotics protecting animals may also protect the humans who consume them. Many tested strains of probiotic bacteria can be used for individualized therapy. The recently isolated Lactobacillus plantarum R2 Biocenol™ has proven to be preferential in aquaculture, and potential benefits in humans are expected. A simple oral dosage form should be developed to test this hypothesis by a suitable preparation method, i.e., lyophilization, allowing the bacteria to survive longer. Lyophilizates were formed from silicates (Neusilin® NS2N; US2), cellulose derivates (Avicel® PH-101), and saccharides (inulin; saccharose; modified starch® 1500). They were evaluated for their physicochemical properties (pH leachate, moisture content, water absorption, wetting time, DSC tests, densities, and flow properties); their bacterial viability was determined in conditions including relevant studies over 6 months at 4 °C and scanned under an electron microscope. Lyophilizate composed of Neusilin® NS2N and saccharose appeared to be the most advantageous in terms of viability without any significant decrease. Its physicochemical properties are also suitable for capsule encapsulation, subsequent clinical evaluation, and individualized therapy.

Effects of Different Dietary β-Glucan Levels on Antioxidant Capacity and Immunity, Gut Microbiota and Transcriptome Responses of White Shrimp (Litopenaeus vannamei) under Low Salinity

β-Glucan could significantly improve the antioxidant capacity of aquatic animals. The effects of different dietary levels (0 (control), 0.05, 0.1, 0.2 or 0.4%) of β-glucan on the growth, survival, antioxidant capacity, immunity, intestinal microbiota and transcriptional responses of Litopenaeus vannamei under low salinity (≤3) were investigated. The dietary growth trial lasted 35 days (initial shrimp 0.26 ± 0.01 g). The results indicated that the growth performance of the 0.1% and 0.2% groups was significantly better than that of the control group. A second-order polynomial regression analysis of growth performance against dietary β-glucan indicated that the optimal dietary β-glucan level was 0.2% of dry matter. The digestive enzyme activity of the hepatopancreas was enhanced with increasing β-glucan levels. The antioxidant and nonspecific immunity capacities of the hepatopancreas were also enhanced in the 0.1% group. The α-diversity index analysis of the intestinal microbiota showed that the intestinal microbial richness of L. vannamei increased in the 0.1% group. The relative abundance of Proteobacteria decreased in the 0.1% group compared with the control group. The transcriptome results indicate that the prebiotic mechanisms of β-glucan include upregulating the expression of nonspecific immune genes and osmoregulation genes and activating KEGG pathways associated with carbohydrate metabolism under low-salinity stress. These results suggested that dietary supplementation with β-glucan markedly increased growth performance and alleviated the negative effects of low-salinity stress by contributing to the activity of biochemical enzymes and enriching carbohydrate metabolism in L. vannamei.