Transplanting Cetobacterium can alleviate acute ammonia intoxication by promoting the synthesis of ornithine of yellow catfish

Effective methods are crucial for handling ammonia overload (AO) in aquaculture to promote the cultivation of fish. Recent studies have shown that acute AO can lead to a notable rise of probiotic Cetobacterium. However, further investigation is needed to determine if this effect persists under chronic AO. In this study, yellow catfish were exposed to environmentally relevant AO of 0, 0.06, and 0.6 mg/L NH₃ (30 °C, pH = 7.5) for 8 weeks. Results indicate that chronic AO can elevate intestinal Cetobacterium abundance from 3.67 % to 30.93 %. This shift could potentially serve as a protective response against AO. Another experiment was conducted to investigate the ammonia reduction mechanism of Cetobacterium. The experimental design entailed the CON and CS groups received 1 × 10⁸ CFU/mL heat-killed and live Cetobacterium administration (CA) without AO treatment, respectively. The 1 × 10⁸ CFU/mL heat-killed and live CA with 125 mg/L T-AN AO treatment, designated as the AM and AMCS groups, respectively. Results showed that CA increased Cetobacterium colonization from 3 % to 50 % and improved survival rate from 43.33 % to 76.67 %. It also reduced ammonia levels in the serum, liver, and intestines from 1516.67 μmol/L, 1382.72 μmol/L, and 600.62 μmol/L to 427.78 μmol/L, 808.02 μmol/L, and 414.81 μmol/L by upregulating ureagenesis genes (otc, asl, ass, and arg) in the intestines and liver. Metabolomics analysis revealed that CA enhances intestinal ornithine, argininosuccinic acid, and urea levels, which were crucial metabolites for ureagenesis. Consequently, CA can boost ureagenesis by stimulating intestinal ornithine and argininosuccinic acid synthesis. Additionally, supplementing 0.15 % of ornithine to the diet reduced serum ammonia from 804.8 μmol/L to 298.4 μmol/L, and urea increased from 51.4 μmol/L to 132.4 μmol/L under acute AO conditions. Concurrently, these findings suggest that CA can facilitate host ammonia detoxification via ornithine production. Our study emphasizes the evidence and mechanisms of intestinal microbiota in ammonia detoxification.