Oxytetracycline-induced microbiota depletion attenuates β-glucan-mediated intestinal protection in grouper: Evidence from morphology, antioxidant capacity, and microbial biomarkers

Our previous research found that dietary β-glucan enhanced intestinal health in grouper, yet whether these benefits are strictly dependent on the gut microbiota remains unclear. To verify the causal link between gut microbiota and β-glucan efficacy, this study aimed to determine whether oxytetracycline (OTC)-induced microbiota depletion would attenuate the intestinal protective effects of β-glucan in pearl gentian grouper ( Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). Healthy groupers were randomly allocated to 12 tanks, with three replicates assigned to each dietary treatment group: the control diet (CD) group, the 0.1% yeast β-glucan diet (GD) group, and the 0.1% yeast β-glucan diet supplemented with 0.2% OTC (GOD) group. The results demonstrated that GD group (compared to CD) and GOD group (compared to GD) did not significantly influence growth performance parameters, including final body weight, weight gain rate, survival rate, specific growth rate, and feed conversion ratio. Compared to the GD group, the GOD group led to a significant reduction in intestinal muscularis thickness and villi height (P < 0.05). Furthermore, the content of malondialdehyde was significantly elevated in the GOD group, while the activity of superoxide dismutase and the mRNA expression level of catalase were significantly reduced (P < 0.05). Furthermore, no significant differences were observed in the α-diversity indices of gut microbiota among the three dietary groups. However, analysis using Random Forest Classifier revealed that the most significant microbial biomarkers associated with intestinal damage were Lactobacillus salivarius , Faecalibacterium prausnitzii , and Pseudogulbenkiania subflava (P < 0.05). In conclusion, OTC-induced microbiota depletion attenuated the beneficial effects of dietary β-glucan on intestinal health in pearl gentian grouper, as evidenced by compromised gut tissue morphology, reduced antioxidant capacity, and increased apoptosis. This study suggest that the modulation of gut microbiota structure plays a pivotal role in mediating the intestinal health benefits conferred by dietary β-glucan. • Antibiotic depletion attenuated β-glucan-induced morphological improvements. • Microbiota depletion impaired intestinal antioxidant capacity and increased apoptosis. • β-glucan promotes intestinal homeostasis in a microbiota-dependent manner.