A preliminary metagenomic and metabolomic investigation into the effects of Aspergillus niger cultures on microbial homeostasis and antibiotic resistance gene profiles in the rumen of fattening sheep.

Abstract

Background: Under high-concentrate feeding conditions, ruminants often experience rumen microecological imbalance and dysfunction, which can impair growth performance and increase the risk of antibiotic resistance gene (ARG) dissemination.

Results: To evaluate the ameliorative effects of Aspergillus niger (A. niger) cultures, fattening sheep were randomly allocated into the following five groups: a control group (CON), a control diet supplemented with 250, 500, or 1,000 mg/kg A. niger cultures (designated as LA, MA, and HA, respectively); and an antibiotic group supplemented with 5,000 mg/kg chlortetracycline premix (AN). Microbial community analysis indicated that several bacterial taxa, including Succinivibrio sp900317105, Prevotella sp002353485, Quinella sp017515635, Quinella sp015206805, and Prevotella sp900320255, were significantly enriched in the A. niger culture-supplemented groups (P < 0.05). ARG profiling showed that the abundance of tetracycline resistance genes was significantly lower in all A. niger groups compared with the CON and AN groups (P < 0.05), while β-lactam resistance genes were significantly reduced in the HA group (P < 0.05). Furthermore, the abundances of Rank I and Rank II ARGs were significantly higher in the AN group than in the other groups, whereas the abundances of Rank II and Rank IV ARGs were significantly lower in the A. niger culture groups than in the CON and AN groups. Metabolomic analysis further demonstrated that supplementation with A. niger cultures significantly decreased the concentration of N-decanoyl-L-homoserine lactone (P < 0.05) while increasing the levels of N-3-oxotetradec-7Z-enoyl-L-homoserine lactone, indole-3-methyl acetate, and indole-3-propionic acid (P < 0.05).

Conclusions: These findings suggest that A. niger cultures can reduce the abundance of ARGs and mitigate the risk of ARG dissemination by modulating the rumen microbial community and associated metabolites.