Illuminating the Black Box: Trace Element Biogeochemistry from a Microbial Perspective.

Area of Science:

• Environmental microbiology
• Geochemistry
• Biogeochemical cycles

Background:

• Microbial processes significantly impact the environmental fate of trace elements such as mercury (Hg) and arsenic (As).
• Complexities in microbial transformation rates and human impacts hinder accurate environmental modeling.
• Key microbial processes include redox reactions, energy generation, resource limitation, and ecological/evolutionary factors.

Purpose of the Study:

• To highlight critical processes governing microbial activity in trace element transformation.
• To compare and contrast microbial mercury and arsenic cycling, noting genetic underpinnings.
• To advocate for experimental approaches integrating contaminant transformation with microbial community activity.

Main Methods:

• Literature review and synthesis of microbial trace element transformations.
• Comparative analysis of mercury (Hg) and arsenic (As) biogeochemical cycles.
• Discussion of genetic basis for microbial transformations (e.g., hgcAB, mer, arsH).

Main Results:

• Microbial transformations of Hg and As serve diverse roles: metabolism, detoxification, warfare, and unknown functions.
• Specific examples include arsenate to arsenite conversion, Hg(II) to Hg(0) reduction, and As(III) methylation.
• Methylmercury formation from Hg(II) represents a significant toxicological concern.

Conclusions:

• A microbe-centric framework is essential for advancing conceptual and quantitative models.
• Integrating contaminant transformation data with microbial activity metrics is crucial.
• This approach will improve forecasting of environmental and human exposure to trace element contaminants.