Toxicity of titanium dioxide nanoparticles on the histology, liver physiological and metabolism, and intestinal microbiota of grouper

Titanium dioxide nanoparticles (nano-TiO2) are a common environmental pollutant threatening aquatic animals. The natural habitats and cultured environments of groupers make them vulnerable to nanoparticle pollution. In this study, hybrid grouper juveniles were separately exposed to 1 or 10 mg/L nano-TiO2 for 14 days, and the toxicological response of these groupers were investigated. After nano-TiO2 exposure, the liver showed apparent histopathology and intestinal goblet cells were also affected. The transcription of antioxidant and apoptosis-related genes were down-regulated, and the inflammatory factor TNF-alpha was up-regulated in the liver. The metabolite patterns of the liver were disturbed, especially amino acid metabolism. The diversity and composition of the intestinal microbiota were also altered especially the genera Lactobacillus and Nautella. The changes of several intestinal bacteria were correlated with the immune factors and metabolites of respective hosts. We concluded that nano-TiO2 exposure negatively affects the physiological homeostasis of groupers.