About this Research Topic
Several recent breakthroughs have significantly advanced our understanding the processes involved in the cycling of mercury (Hg) in nature. The discovery of hgcAB, a gene pair that specify microbial methylation, has dramatically changed our understanding of the diversity and distribution of Hg-methylating microbes, challenging our ability to constrain environmental variables affecting Hg bioavailability. Other important knowledge gaps remain, such as the native role of HgcA and HgcB, or the possible implication of alternative methylation mechanisms. Traditionally, methylmercury degradation has been thought of as either a photochemical process, or a microbial Hg detoxification process, specified by the mercury resistance (mer) operon. However, recent research has added to this picture by suggesting process-based explanations for the rapid rates of anoxic and often abiotic demethylation. New findings include a novel dark abiotic demethylation process, driven by reduced sulphur, and the observation of mer-independent demethylation by methylotrophs and by green algae. Finally, newly discovered Hg reduction by anaerobes via the co-metabolic generation of reducing power suggests paths for Hg redox transformations in anoxia, the environmental importance of which remains to be tested.
The goal of modelling, and thus predicting, Hg cycling in the environment remains elusive in large part because individual processes are still poorly understood or parameterized. In this Research Topic, we seek to bring together a group of papers describing cutting edge research that advances knowledge of fundamental biogeochemical processes that contribute to Hg biogeochemical cycles. These include methylation, methylmercury degradation, and Hg oxidation and reduction. This group of papers would address the major challenge of incorporating both geochemistry and microbial community dynamics, i.e., abundance, diversity, and activity as related to Hg cycling processes, into conceptual models of net methylmercury accumulation. We particularly encourage papers from the Hg transformation sessions of the recent International Conference on Mercury as a Global Pollutant. We would like to dedicate this Research Topic to the memory of our colleague Dr. Mark Hines.
This Research Topic focuses on recent advances in our understanding of the processes and organisms that contribute to Hg methylation, methylmercury degradation, and Hg oxidation and reduction in the environment. We welcome original research papers, perspectives, and mini-reviews on:
• The role of microbial community structure in Hg cycling, especially in poorly understood environments like the oceans
• New approaches to understanding the role of microbes in Hg cycling
• Process-based explanation for the widely observed high rates of methylmercury degradation in anaerobic sediment and soil incubations.
• The role of syntrophy and anaerobic co-metabolic processes in microbial Hg cycling
• The rapidly evolving role of sulphur chemistry in Hg cycling
• The role of unculturable putative Hg-methylators in Hg methylation
• Development of process-based biogeochemical models of Hg cycling
• Microbially-induced redox cycling of Hg
Keywords: Mercury, environment, geochemistry, microorganisms, transformations
Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.
