Mercury (Hg) biotransformation is an important process that can affect the speciation and bioaccumulation of Hg in fish. The intestinal microbiota has been suggested to take part in this process. However, Hg biotransformation in fish is still unclear and the responses of gut microbiota to different Hg exposure scenarios have not been well addressed. The present study investigated the bioaccumulation and biotransformation of Hg in a freshwater fish (Micropterus salmoides) and characterized the gut microbiome community under dietary inorganic Hg (IHg) or methylmercury (MeHg) exposure, aiming to evaluate the effects of gut microbiome's activities on the internal-handling and fate of Hg in fish. Significant Hg methylation was observed in fish under IHg exposure, whereas there was no demethylation occurred in MeHg-treated fish. Both IHg and MeHg could significantly alter the community composition of gut microbiome. The administrated IHg in the food could enhance the growth of methylators, resulting in additional MeHg production in fish gut. However, abundance of demethylators was greatly decreased under either IHg or MeHg exposure, leading the demethylation process to be negligible. The results strongly suggested that the behaviors of gut bacterial community played an important role in the presence or absence of biotransformation processes. This study elucidated the importance of gut microbiome in Hg biotransformation process, and helped to develop a novel perspective to understand the Hg bioaccumulation of fish in realistic environment.

汞（Hg）的生物转化是影响鱼类体内汞形态形成和生物积累的重要过程。已建议肠道微生物群参与这一过程。然而，鱼类体内的汞生物转化仍不清楚，肠道微生物群对不同汞暴露情景的反应尚未得到很好的解决。本研究调查了淡水鱼 ( Micropterus salmoides)中汞的生物蓄积和生物转化。) 并描述了膳食无机汞 (IHg) 或甲基汞 (MeHg) 暴露下的肠道微生物群落，旨在评估肠道微生物群的活动对鱼类体内汞的内部处理和命运的影响。在 IHg 暴露下的鱼中观察到显着的 Hg 甲基化，而在 MeHg 处理的鱼中没有发生去甲基化。IHg 和 MeHg 都可以显着改变肠道微生物组的群落组成。食物中施用的 IHg 可以促进甲基化因子的生长，导致鱼肠中产生额外的 MeHg。然而，在 IHg 或 MeHg 暴露下，去甲基化剂的丰度大大降低，导致去甲基化过程可以忽略不计。结果强烈表明肠道细菌群落的行为在生物转化过程的存在与否中起着重要作用。该研究阐明了肠道微生物组在汞生物转化过程中的重要性，并有助于开发一个新的视角来了解鱼类在现实环境中的汞生物积累。