Session Title :

Organisms, pathways and regulations behind biological methylmercury production from the cell to the ecosystem

Synopsis :

This proposed session will focus on the latest advances in our understanding of the environmental conditions that are favorable for mercury methylation, the biochemical pathways for uptake, transformation, and release as well as the genetic determinisms and regulations required and their overall significance for mercury speciation fate and impact on biomagnification and health. Recent advances in experimental methods and analytical techniques that further our understanding in laboratory and field investigations will also be highlighted.

Description :

If microbial activities play a major role in mercury methylation we still only have a vague idea of the overall environmental parameters and the underlying mechanisms (uptake, transformation rates, regulation) controlling the net methylmercury production at the ecosystems level. Many studies have led to the implication of the sulfate- and iron- reducers in methylmercury production. Nevertheless, microbial communities are complex physiological networks and methylmercury production (the result) depends on many individual activities (still a relatively black box). All these activities vary with environmental conditions. Thus, the determination of the truly relevant environmental factors, both biotic and abiotic, that regulate and /or stimulate methylmercury production are also of great interest from the cell to the population level. Indeed, many data were obtained recently on the mobility, availability and uptake of mercury in the environment and by particular microorganisms. They permitted for example to understand mercury uptake mechanisms or to localize the different mercury species in sub-cellular fractions. In addition, substantial effort has been put forth towards the identification and characterization of the enzymatic systems, their corresponding genes, and the possible regulatory factors of these genes that are responsible for biogenic mercury methylation. Identification and gaining a comprehensive understanding of the factors stimulating expression of the functional genes responsible for mercury methylation will permit a more informed path for teasing out the environmental conditions that enhance or inhibit methylmercury production in situ in the near future, thereby permitting accurate potential risk assessments for ecosystems.

All the data accumulated over the last few years have modified our view on the global mercury biogeochemical cycle and thus on the potential methylmercury sources. Integrated approaches combining molecular-scale genomics, biochemistry and field studies are necessary to understand methylmercury production in ecosystems. This session proposes to integrate these latest advances.