|Abstract Title:||MeHg Formation by Geobacter Sulfurreducens Driven by Hg Speciation and Cell Physiological State|
|Presenter Name:||Mareike Franziska Gutensohn|
|Company/Institution:||Umeå University, Sweden|
|Session:||Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling|
|Co-Authors:||Mareike Franziska Gutensohn,Jeffra Schaefer,Ulf Skyllberg,Erik Bjrn|
Abstract Information :
The formation of the neurotoxin methylmercury (MeHg) is a biotic process where anaerobic bacteria methylate inorganic divalent Hg (HgII) intracellularly. The cellular uptake mechanisms are still not fully identified, but low molecular mass (LMM) thiols (RSH) play an important role together with RSH groups on the outer membrane in controlling the chemical speciation and availability for uptake of HgII. Increased concentration of specific LMM-RSH, especially cysteine, is known to enhance the formation of MeHg. The mechanisms for the observed enhancement effects and correlation are, however, not fully clear. Some studies have ascribed the enhancement to chemical speciation effects, i.e. formation of Hg(LMM-RS)2 complexes with a presumed high availability for cellular uptake and methylation. Moreover, metabolically active anaerobic microorganisms produce LMM-RSH in vivo and export them to the assay medium with concentration sufficient to affect the chemical speciation of HgII. Beside HgII speciation, it was proposed that LMM-RSH compounds affect HgII methylation also by other mechanisms. Previous bacteria assay studies have been conducted using experimental assays with minimalized defined assay buffer to easily control the assay environment. In this study we systematically investigated the role of LMM-RSH compounds on MeHg formation by the iron-reducer Geobacter sulfurreducens under more complex assay media containing biogenic metabolites or enhanced nutrient composition compared to standard assays. We specifically tested if the mode of action of LMM-RSH are different depending on medium composition and physiological state of cells. We further studied the time dynamics in the concentration of LMM-RSH compounds in the medium during varying assay conditions, and its impact on time-dynamics in HgII speciation and methylation. Taken together, our results point to a time-dependent MeHg formation driven by a complex interplay between physiological state of bacteria cell and HgII speciation.