New insights into β-glucan-enhanced immunity in largemouth bass Micropterus salmoides by transcriptome and intestinal microbial composition

Abstract

β-glucan is widely used in aquaculture due to its immunostimulatory effects, but the specific effect and potential regulatory mechanism on largemouth bass (Micropterus salmoides) are still unclear. Here, we evaluated the effects of β-glucan on growth, resistance to Aeromonas schubertii, intestinal health, and transcriptome of largemouth bass to reveal the potential regulators, metabolic pathways, and altered differential microbiota. Four experimental diets were designed with β-glucan supplementation levels of 0 (control), 100 (LA-100), 200 (MA-200), and 300 (HA-300) mg kg-1, and each diet was fed to largemouth bass (79.30 ± 0.50 g) in triplicate for 70 days, followed by a 3-day challenge experiment. Results showed that different β-glucan supplementations had no significant effects on growth performance and whole-body composition. Fish fed a diet with 300 mg kg-1 β-glucan significantly increased the activity of lysozyme than those fed diets with 0 and 100 mg kg-1 β-glucan. In addition, the survival rate of largemouth bass in β-glucan supplementation groups was significantly higher than the control group at 12- and 24-h challenge by Aeromonas schubertii. Transcriptome analysis showed that a total of 1,245 genes were differentially expressed [|log2(fold change)| ≥1, q-value ≤0.05], including 109 immune-related differentially expressed genes (DEGs). Further analysis revealed that significantly upregulated and downregulated DEGs associated with immunity were mapped into 12 and 24 pathways, respectively. Results of intestinal microflora indicated that fish fed a diet with 300 mg kg-1 β-glucan had higher bacterial richness and diversity as evaluated by Sobs, Chao, Ace, and Simpson indices, but no significant differences were found in the comparison groups. Furthermore, 300 mg kg-1 β-glucan significantly increased the relative abundance of Mycoplasma and decreased Proteobacteria (mainly Escherichia-Shigella and Escherichia coli) and Bacillus anthracis in largemouth bass intestinal microflora. The findings of this study provided new insights that will be valuable in future studies to elucidate the mechanism of immunity enhancement by β-glucan.

Evaluate of Wheat Gluten as a Protein Alternative for Fish Meal and Soy Protein Concentrate in Red Spotted Grouper Epinephelus akaara

“…Each tank was manually fed four times per day (08:00 a.m., 11:30 a.m., 3:00 p.m., and 6:30 p.m.), with 30 min per meal to ensure apparent satiety. After each feeding, the remaining feed pellets in each tank were counted according to the method of Zhang et al [ 29 ] and siphoned out immediately. The daily feeding rate was tentatively set at 10% in excess based on the average intake over the past three days, and fish could receive more feed if they showed signs of feeding.…”

The Zootechnical Performance, Health State Modulation, Morphology, and Intestinal Microbiome of Nile Tilapia Juveniles Fed with a Functional Blend of Immunostimulants Associated with a Diet High in Soybean Meal

“…β-glucans are carbohydrates composed of glucose molecules, which are the main structural components of fungal, bacterial, plant, and algal cell walls [14]. These compounds differ in molecular weight and branching degree depending on their source [14,15]. These polysaccharides can be recognized by the immune systems of different vertebrate species and can promote a healthier gut due to their prebiotic effects [15].…”

“…These compounds differ in molecular weight and branching degree depending on their source [14,15]. These polysaccharides can be recognized by the immune systems of different vertebrate species and can promote a healthier gut due to their prebiotic effects [15].…”

The Combination of β-Glucan and Astragalus Polysaccharide Effectively Resists Nocardia seriolae Infection in Largemouth Bass (Micropterus salmoides)

“…Relevant reports indicate that β-glucan can influence both innate and adaptive immune responses, thereby enhancing disease resistance in aquaculture species [30][31][32][33][34]. Similarly, the oral administration of β-glucan activated the nonspecific immune response in largemouth bass, enhancing their resistance against Aeromonas schubertii [35]. The application of immunostimulants to enhance fish immunity against pathogens is an effective strategy for addressing disease outbreaks.…”