Mechanisms of Cellular Mercury (II) Uptake by Mercury Methylating Bacteria

Methylmercury (MeHg), a highly toxic neurotoxin, is mediated by methylating microorganisms from inorganic divalent mercury, Hg(II).

Therefore, the cellular uptake of Hg(II) is considered to be the first critical step of MeHg production, yet remains unclear.

Thiol functional groups (RSH) in different subcellular compartments of bacteria assumedly play important and different roles in the uptake and methylation of Hg(II). However, the abundance and chemical characteristics of these thiols have not been studied in detail.

In this project, we will quantify the subcellular distribution (such as outer membranes, inner membranes, periplasm, and cytoplasm) of thiol functional groups in a model mercury methylating bacterium.

Furthermore, the distribution and chemical speciation of mercury and sulfur will be quantified and localized to subcellular compartments as a function of time by use of synchrotron X-ray spectroscopy methods (XANES, EXAFS, nano-XRF).

Based on this quantified, spatial and temporal information, proposed mechanisms of Hg(II) uptake and internalization can be tested and a new mechanistic model involving the roles of different types of thiols at the subcellular scale will be formulated.

The project is the first in its kind and is expected to provide information that in a longer-term is necessary for developing a deeper understanding on how society may take action to limit net MeHg formation in critical soil and water environments.