Comparative analysis of intestinal microbiota and its function on digestion and immunity of juvenile abalone Haliotis discus hannai fed two different sources of dietary soybean protein

The present study evaluated the replacement of fish meal (FM) with two different soybean protein sources (soybean protein concentrate (SPC) and soybean meal (SBM)) on the intestine microbiota of abalone Haliotis discus hannai and the implications for the host intestinal function and health. The control diet with FM as the main protein source (CON), and the four experimental diets with 50 % and 100 % SBM replacing FM (SBM50 and SBM100), and 25 % and 100 % SPC replacing FM (SPC25 and SPC100) were fed to abalone for 110 days. The intestinal microbiota analysis results revealed that there were no significant differences in α-diversity indices (Chao1, Ace, Sobs, and Shannon) among all groups. However, analysis of similarity (ANOSIM) demonstrated dramatic shifts in the intestinal microbiota component at the genus level among the groups. Venn diagram analysis identified 470 overlapping operational taxonomic units (OTUs) across the five groups, with the SBM50 and CON groups exhibiting the highest and lowest number of unique OTUs, respectively. Firmicutes and Proteobacteria were the predominant phyla in abalone, with Mycoplasma being the dominant genus (CON: 42.95 %; SBM50: 23.98 %; SBM100: 49.32 %; SPC25: 27.20 %; SPC100: 34.25 %). Notably, the pathogens Vibrio abundance in the SPC25 group was significantly lower than in the CON group. The intestinal microbiota networks in the CON, SBM50, SBM100, SPC25, and SPC100 groups consisted of 1757, 2140, 1992, 2281 and 1747 edges, respectively. Furthermore, correlation heatmap results suggested that digestive enzymes and immune indices in abalone were associated with specific intestinal microbiota. Functional prediction via the KEGG pathway analysis revealed that the replacement levels of dietary FM with SBM and SPC significantly affect various biological functions of the intestinal microbiota. In summary, feeding SBM (50 %) and SPC (25 %) diets to abalone increased the abundance of beneficial bacterium in the intestines, contributing to improved digestion and increased growth rate of abalone.