Responses of host intestine and intestinal microbiota under dietary methylmercury exposure in marine fish

Abstract

Mercury (Hg) in fish has arouse public attention for decades, thus fish (e.g., rabbitfish, Siganus fuscescens) accumulating low Hg are the wise choices for human consumption. High Hg burdens are usually found in fish occupied at high trophic levels as a result of the biomagnification of MeHg through food chains. However, more Hg accumulation was found in fish at higher trophic level when fed with the same diet in the fish farm. The mechanisms for the differential Hg accumulation among fish species remain unclear. In this study, we investigated the roles of intestine and intestinal microbiota played in different fish species under dietary MeHg exposure. The results suggested that Hg accumulation in rabbitfish (Siganus fuscescens) and grouper (Epinephelus coioides) was dose-dependent and differed among organs. Interestingly, reduced Hg accumulation was observed in both rabbitfish and grouper under dietary MeHg and antibiotic florfenicol exposure. However, the mechanisms for the reduced Hg accumulation in different fish species were distinct. The increased excretion of Hg from intestine was the dominant reason for the reduced Hg accumulation in fish since the major excretion transporters for Hg (amino acid transporters, GSH transporters and ABCB) were significantly expressed in rabbitfish. On the contrary, the low Hg accumulation was dominantly ascribed to the reduced absorbed Hg via intestine because no transporter for Hg excretion highly expressed in grouper in the 25 differentially expressed genes (DEGs). Therefore, the intestinal microbiota activities were the predominant factors for the low Hg accumulation in grouper. However, only a few intestinal microbiota species associated with Hg metabolism were found in both rabbitfish and grouper. And the specific functions of intestinal microbiota for the Hg metabolisms need further study because of the presence of large amounts of unidentified bacteria species. This study provides important evidence for Hg metabolic pathway in fish with low Hg body burden.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology