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Abstract Title: Hg methylation in relation to phenotypic differences of Geobacter sulfurreducens biofilms
Presenter Name: Elena Yunda
Company/Institution: Umeå University
Session: Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling
Day and Session: Friday 29th July - Session Two
Start Time: 09:30 UTC
Co-Authors: Elena Yunda,Quynh Nhu Phan Le,Madeleine Ramstedt,Erik Björn

Abstract Information :

Recent research has pointed to microbial biofilms as an important source of methylmercury (MeHg) in natural aquatic systems, but little is known about mechanistic principles of MeHg formation in biofilms. The overall aim of this work was to develop an experimental platform for studying MeHg formation in biofilms of Geobacter sulfurreducens. The specific objectives included characterizing biochemical composition and quantifying biomass volume of G. sulfurreducens biofilms in different nutritive media, determining MeHg formation capacity of these biofilms, and calculating partitioning of MeHg and inorganic Hg between biofilms and bulk medium volume. The biofilms were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, confocal laser scanning microscopy and cryo- scanning electron microscopy. MeHg and total Hg were quantified using ICPMS based methods. The results showed that after 72 hours of growth, G. sulfurreducens developed a biofilm containing high density of cells and a rich extracellular matrix. MeHg was formed in all studied biofilms, and the partitioning coefficient ?biofilm/medium? was higher for MeHg than for inorganic Hg, suggesting rapid Hg methylation by biofilm cells. Furthermore, a change in electron acceptor source in the medium (ferrihydrite versus fumarate) and overall nutrient content (varied by addition of yeast extract) affected metabolic features of biofilm cells, e.g. polysaccharide synthesis and cytochrome redox status, as well as biofilm cell volume. The biofilm cell volume was a determining factor in the extent of MeHg formation among biofilms. The findings of this work illustrate a novel approach to study Hg transformations by G. sulfurreducens in biofilm systems and contribute to the knowledge of how nutrient changes affect biofilm phenotype and Hg methylation capacity.

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