This study aimed to evaluate the effects of dietary supplementation of compound polysaccharides derived from Astragalus and Glycyrrhiza on growth performance, meat quality, antioxidant function, cecal microbiota and serum metabolomics of broilers. A total of 480 one-day-old male Arbor Acres (AA) broilers were randomly divided into four treatments with six replicates comprising 20 broilers each. Treatments: CON group was the basal diet; ANT group was supplemented with Terramycin calcium; LAG group was supplemented with 150 mg/kg Astragalus polysaccharides and 75 mg/kg Glycyrrhiza polysaccharides; HAG group was supplemented with 300 mg/kg Astragalus polysaccharides and 150 mg/kg Glycyrrhiza polysaccharides. The results showed that LAG and HAG supplementation increased growth performance, antioxidant function and meat quality compared with the CON group and ANT group and, especially, the effect of LAG treatment was better than HAG. Analysis of cecal microbiota showed that LAG and HAG supplementation altered cecal microbial diversity and composition in broilers. Serum metabolomics analysis showed that a total of 193 differential metabolites were identified in CON and LAG groups, which were mainly enriched in linoleic acid metabolism and glutathione metabolism pathways. Moreover, there was a close correlation between serum metabolites, cecal microbiota and phenotypic indicators. Conclusion: Dietary supplementation of 150 mg/kg Astragalus polysaccharides and 75 mg/kg Glycyrrhiza polysaccharides could improve the growth performance, antioxidant function and meat quality of broilers by changing the serum metabolites and cecal microbiota composition.

Aflatoxin B₁ (AFB₁) contamination seriously threatens nutritional safety and common health. Bacterial CotA-laccases have great potential to degrade AFB₁ without redox mediators. However, CotA-laccases are limited because of the low catalytic activity as the spore-bound nature. The AFB₁ degradation ability of CotA-laccase from Bacillus licheniformis ANSB821 has been reported by a previous study in our laboratory. In this study, a Q441A mutant was constructed to enhance the activity of CotA-laccase to degrade AFB₁. After the site-directed mutation, the mutant Q441A showed a 1.73-fold higher catalytic efficiency (k_cat/K_m) towards AFB₁ than the wild-type CotA-laccase did. The degradation rate of AFB₁ by Q441A mutant was higher than that by wild-type CotA-laccase in the pH range from 5.0 to 9.0. In addition, the thermostability was improved after mutation. Based on the structure analysis of CotA-laccase, the higher catalytic efficiency of Q441A for AFB₁ may be due to the smaller steric hindrance of Ala441 than Gln441. This is the first research to enhance the degradation efficiency of AFB₁ by CotA-laccase with site-directed mutagenesis. In summary, the mutant Q441A will be a suitable candidate for highly effective detoxification of AFB₁ in the future.