Reshaping fish intestinal microbiota and facilitating barrier function by ZnO nanoparticles

Abstract

Nano-Zn (nZnO) has been increasingly applied in different fields, but the mechanisms of their uses as nutritional sources are less understood. Our study presents a regulatory mechanism of intestinal microbiota and structure mediated by nano-Zn, which subsequently improves the health and growth of fish. Fish diets were supplemented with 60 mg Zn kg⁻¹ ZnSO₄ (metal salt as the control group), 60 mg Zn kg⁻¹ nZnO (powder), or 170 mg Zn kg⁻¹ nZnO (powder) and then fed to golden pompanos for 5 weeks. We employed a new analytical amplicon sequence variant (ASV) method to identify the bacterial species and achieved the first in situ spatial quantification of fish tissue samples. Our results indicated that 60 mg Zn kg⁻¹ of dietary nZnO promoted the probiotic colonization (Lactic-acid bacilli spp.) in the intestine. Upon exposure to a higher nZnO dose (170 mg Zn kg⁻¹), Brevinema and Mycoplasma colonized in the fish intestine as pro-inflammatory microorganisms, which activated the C5 isoprenoid biosynthesis pathway and NAD biosynthesis. Furthermore, dietary nZnO (60 mg Zn kg⁻¹) up-regulated the expression of genes related to intestinal mucus secretion and accelerated the goblet cell renewal in the intestinal villi. At a dose of 170 mg Zn kg⁻¹ nZnO, the fish intestine significantly down-regulated occludin and mucin gene expression while displaying lower villus height, villus area, and goblet cell numbers, which ultimately led to abnormal digestion and absorption and immune functions. The Mantel test confirmed that the intestinal microbial abundance was significantly correlated with the changes in the intestinal structure, and the value of villi-to-crypt ratio decreased with the increase in Vibrio abundance, which was validated by the key genes and serum biochemical indexes. Finally, nZnO could regulate the glucose and lipid metabolism of fish by regulating microorganisms. Our results provided important insights into the interaction between nZnO and fish intestinal microbial community and host.