The role of intestinal microbiota of the marine fish (Acanthopagrus latus) in mercury biotransformation

Both inorganic (IHg) and organic (MeHg) forms of Hg can be converted into each other by methylation or demethylation, leading to changes of Hg speciation and distribution in fish. However, Hg biotransformation in fish is not thoroughly understood and the key factors in this process are unclear. The present study investigated the in vivo Hg transformation in a marine fish (Acanthopagrus latus) and explored the roles of intestinal microbiota in Hg biotransformation. We first demonstrated that Hg methylation or demethylation occurred in the fish gut under dietary IHg or MeHg exposure, respectively. The demethylation was observed to be faster than methylation, suggesting that demethylation could significantly influence the Hg speciation in fish. This study also strongly suggested that intestinal microbiota played a predominant role in Hg biotransformation and thus significantly affected the overall Hg accumulation and distribution in fish body. The richness of Hg methylators or demethylators was elevated under IHg or MeHg treatment, respectively. Furthermore, the intestinal microbiota composition was also altered by Hg exposure. This study highlights the importance of intestinal microbiota in Hg biotransformation in fish body, and suggests that modulating the gut microbiome could be a possible solution to minimize Hg contamination in fish.