Acute effects of mercury on brine shrimp: First evidence highlighting the molecular mechanism through integrated transcriptome and metabolomic analysis

Mercury poses significant hazards to aquatic organisms, causing neurotoxicity, and metabolic disorders. Research on the dynamic distribution of mercury within zooplankton is limited, and the metabolic mechanisms of mercury in zooplankton remain unclear. In this study, we employed a mercury-specific fluorescent probe (aggregation-induced emission luminogen, AIEgen) to visualize the in vivo distribution of Hg²⁺ and MeHg in brine shrimp. Both Hg²⁺ and MeHg accumulated predominantly in the head, ocellus, midgut, and midgut-hindgut transition, with Hg²⁺ further affecting the hindgut and anal opening. Transcriptomics and metabolomics analyses revealed that Hg²⁺ exposure in the midgut likely induced the efflux activity of ABC transporters. The linoleic acid metabolism, α-linolenic acid metabolism, tryptophan metabolism, and retinol metabolism pathways were potentially associated with MeHg accumulation in the head and ocellus. Additionally, the cytochrome P450 pathway participated in detoxification. Enzyme assays and multi-omics data further demonstrated that both Hg²⁺ and MeHg elicited oxidative stress and impaired growth, development, and energy metabolism in brine shrimp. Integrated omics analysis revealed that glutathione metabolism is highly associated with Hg²⁺, while glycerophospholipid metabolism is highly associated with MeHg. Our study revealed the toxicity effects of mercury in zooplankton brine shrimp and promoted the understanding of the underlying mechanism and coping strategies for mercury toxicity in the zooplankton of the aquatic food chain.