AUTHOR=Zhang Yuexing , Guo Mingyu , Li Ning , Dong Zhiyong , Cai Linwei , Wu Bowen , Xie Jianjun , Liu Liang , Ren Lina , Shi Bo 

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

JOURNAL=Frontiers in Immunology

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.1086103

DOI=10.3389/fimmu.2022.1086103

ISSN=1664-3224

ABSTRACT=β-glucan is widely used in aquaculture due to its immunostimulatory, 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 schubetii, 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 ± 0.50g) in triplicate for 70-day, followed by 3-day challenge experiment. Results showed that different β-glucan supplementations had no significantly effects on growth performance and whole body composition. Fish fed diet with 300 mg kg-1 β-glucan significantly increased activity of lysozyme than those fed diet with 0 and 100 mg kg-1 β-glucan. In addition, 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 1245 genes were differentially expressed (|log2fold change| ≥ 1, q-value ≤ 0.05), including 109 immune-related differentially expressed genes (DEGs). Further analysis revealed that significantly up- and down-regulated DEGs associated with immunity were mapped into 12 and 24 pathways, respectively. Results of intestinal microflora indicated that fish fed diet with 300 mg kg-1 β-glucan had higher bacterial richness and diversity 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 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 study to elucidate the mechanism of immunity enhancement by β-glucan.