Lead induces structural damage, microbiota dysbiosis and cell apoptosis in the intestine of juvenile bighead carp (Hypophthalmichthys nobilis)

Lead (Pb) is an environmental pollutant that can accumulate in fish and humans. In this study, the effects of juvenile bighead carp (Hypophthalmichthys nobilis) on the intestinal structure, gut microbiota and cell apoptosis in the intestine of juvenile bighead carp (Hypophthalmichthys nobilis) after 96 h of Pb exposure were detected. The results showed that the intestinal barrier was severely damaged, including intestinal leukocyte infiltration, goblet cells significantly increased, intestinal villi shortened significantly, and abnormal thickening of the intestinal wall. Meanwhile, the mRNA expressions of structure related genes (villin-1 and Claudin-12) were down-regulated after Pb exposure, while pro-inflammatory factors (IL-8 and TNF-alpha) were up-regulated and peaked at 48 h. It shows that Pb causes intestinal inflammation and destroys intestinal structure. Furthermore, MiSeq sequencing data of the 16S rRNA gene V3-V4 region revealed a reduction in richness and diversity of intestine microbiota after Pb exposed. At the phylum level, the abundance of enteropathogenic bacteria (Proteobacteria and Bacteroidetes) were increased significantly whereas Firmicutes and Cyanobacteria were decreased significantly after exposed to Pb. A more in-depth analysis, at the genus level, a total of 40 intestinal microbes identified by operational taxonomic unit (OTU) analysis were obviously changed at 6 h, 48 h and 96 h after exposure to Pb, and the abundance of pathogenic bacteria such as Chryseobacterium also increased significantly. The functional prediction results of intestinal flora showed that the abundance of apoptosis was down-regulated after Pb exposure. It was consistent with the mRNA expressions of Bid, Caspase-2, and Caspase-3, indicating that apoptosis function of cells and intestinal flora was disturbed. Taken together, it is speculated that Pb may lead to the destruction of the intestinal barrier of bighead carp, leading to the disorder of the intestinal microbial community, which in turn promotes the occurrence of cell apoptosis. Our research provided some evidence for the association between microbiota dysbiosis and cell apoptosis after Pb exposure in the intestine of juvenile bighead carp.