Metal-Ligand Interactions Influence Mercury Transformations in Metabolically-Active Transient Storage Zones

Abstract:

Freshwater resources supplied by headwater streams and their surrounding watersheds are being threatened by severe pollution from anthropogenic releases of nutrients and trace metals such as mercury (Hg). Mercury is the second leading cause of impaired waters in the continental United States and is responsible for fish consumption advisories in all 50 states. Preserving the services for future use requires developing a deeper understanding of how and why metabolically-active transient storage zones (MATSZs) serve as hot spots for biogeochemical transformations. MATSZs are biologically-active surface and subsurface locations (e.g., hyporheic zone) that delay the downstream flow of water in comparison to the main channel. In this presentation, we will provide a brief overview of MATSZs and discuss how these zones influence metal-ligand interactions, availability, and ultimately transformation. We will use a small biomolecule, methanobactin, excreted by methanotrophic bacteria as an example model system.

Methanotrophic bacteria facilitate the acquisition of Cu ions by secreting a small peptide known as methanobactin which strongly bind copper and function as an extracellular Cu recruitment relay analogous to siderophores and iron. In addition to Cu, methanobactins are known to form complexes with other late transition metals, including Hg. Recent results have definitively determined the functional group assignment, electronic structure, and coordination geometry and binding interactions that characterize methanobactin-Hg complexes and explain the observed differences in the ability of anaerobic bacteria to methylate Hg complexed by methanobactins produced by different types of methanotrophs. Illustrating the complexity of metal-ligand interactions and how this complexity can influence transformations in MATSZs.