Postdoctoral Fellowship: OCE-PRF: Elucidating the Microbial Mechanism of Dimethylmercury Formation in the Ocean

Mercury (Hg) in seafood is a major food safety concern, as the neurotoxicant monomethylmercury (MMHg) bioaccumulates in fish and shellfish consumed by people worldwide. In the United States, much of the seafood supply is imported from regions with high Hg emissions, increasing the risk of MMHg exposure for consumers. Elevated MMHg intake is linked to health concerns, including cardiovascular disease and developmental impacts in children, with estimated economic losses exceeding $8 billion annually in the United States. To protect food security and public health, it is critical to understand how Hg is transformed into MMHg in the ocean and enters the marine food web. While most studies focus MMHg formation from inorganic Hg, another related compound, dimethylmercury (DMHg), can degrade and contribute to MMHg sources in seafood, but this remains poorly understood. Recent work has shown that DMHg is produced in coastal surface waters during algal blooms, suggesting that marine microbes play a role in this process. This research will investigate how these microbes produce DMHg and how this process affects the supply of MMHg to food webs. By advancing our understanding of the marine Hg cycle, this work will support seafood safety and public health efforts. This project also supports training for a postdoctoral fellow, building future leadership in environmental health and food security research.

This project investigates the microbial mechanisms of DMHg formation in marine environments. Despite evidence that DMHg demethylation contributes significantly to MMHg supply, DMHg’s formation pathway remains unknown. It is hypothesized that DMHg is microbially produced through either the hgcAB gene cluster similar to MMHg formation, or through novel microbial mechanisms, particularly during periods of algal bloom-driven organic matter remineralization. To test this, the project integrates three complementary research approaches: 1) laboratory culturing of known Hg-methylating microbes (e.g. Desulfovibrio desulfuricans and Geobacter sulfurreducens) to determine if they produce DMHg and whether this process depends on the hgcAB gene; 2) incubation experiments using natural microbial communities collected from Scripps Pier to trace DMHg production and identify active microbial groups; and 3) metagenomic and metatranscriptomic analysis to detect the abundance and expression of hgcAB genes and potential novel genes during the annual bloom cycle. This integrated approach will provide the first mechanistic insights into microbial DMHg production and reveal how environmental conditions influence Hg transformation pathways in oxic marine waters. These findings will improve our understanding of the global Hg cycle and help refine models used to predict MMHg bioaccumulation in marine ecosystems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Award Number: 2513591
Principal Investigator: Hannah Adams
Funds Obligated: $341,396
State: CA