Waterborne Cr3+ and Cr 6+ Exposure Disturbed the Intestinal Microbiota Homeostasis in Juvenile Leopard Coral Grouper Plectropomus Leopardus.

Background: Chromium (Cr) mainly has two stable forms: Cr3+ and Cr6+. Cr and its compound are widely used in the printing, dyeing, leather making, and metallurgy industry. They are evitably released into the environment and pose a significant threat to creatures, for instance, the excessive chromium (Cr) burden in the marine ecosystem is often harmful to fish. Intestinal microbiota greatly affects fish performance, but how waterborne Cr affects fish intestinal microbiota is unclear. To test the hypothesis that the waterborne Cr exposure could significantly affect fish' intestinal microbiota homeostasis, and the effect was highly dependent on Cr concentration and speciation, the juvenile leopard coral grouper Plectropomus leopardus were exposed to waterborne Cr3+ and Cr6+ (0.1, 0.5 ppm) for 7 days, and the intestinal microbiota was determined by Amplicon sequencing of the 16S rRNA. Results: In all Cr treatment groups, the alpha diversity of intestinal microbiota communities of P. leopardus was decreased. The phyla Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi and Bacteroidetes were the dominant intestinal microbiota. The Chao index diversity significantly declined in Cr treatment group, indicating the intestinal microbiota community structure was changed. Among the dominant intestinal microbiota, Proteobacteria was most sensitive to Cr exposure, and it increased after xposure. The PICRUSt predicted that 0.5 ppm Cr3+ expousure caused metabolism disordered in the intestinal of P. leopardus. Conclusions: Waterborne Cr3+ and Cr6+ significantly disturbed intestinal microbiota homeostasis in P. leopardus, including their diversity, composition, and community structure. The metabolism level of intestinal microbiota in P. leopardus was decreased by Cr3+ exposure. High concentrations of Cr3+ may pose potential risks to the intestinal homeostasis of P. leopardus.