Methylmercury (MeHg), an organic Hg compound, is a potent toxin that bioaccumulates in food sources and is primarily produced by microorganisms in anaerobic organic-rich soils and sediments. To date, little is understood about the physiological function of MeHg production. It is postulated that the native function of Hg methylation proteins (HgcAB) is not Hg methylation, but the methylation of an unknown metabolite. Hg methylation has been linked to C1 carbon metabolism for acetyl-CoA and methionine biosynthesis, sometimes as part of the Wood-Ljundahl pathway, yet a specific biochemical pathway remains elusive. Here we suggest a systems biology approach to exploring the physiological function of Hg methylation using Desulfovibrio desulfuricans ND132 as a model organism. D. desulfuricans ND132 is an ideal model organism for studying the role of HgcAB in central metabolism due to its well annotated, closed genome and the availability of targeted gene deletions related to Hg methylation and C1 metabolism. The work to be conducted at EMSL includes LC-MS/MS proteomics and RNA-seq analyses of D. desulfuricans ND132 wild-type and mutant cell cultures. The various D. desulfuricans ND132 gene deletion strains chosen for this study (e.g. delta-hgcAB, delta-metH, delta-cobT, delta-hgcA:T101A ) exhibit various changes in Hg methylation capability compared to wild-type (e.g. 0-246%). Our aim at EMSL is to test the hypothesis that the physiological role of HgcAB is not related to Hg methylation but is linked to microbial central metabolism. A complete metabolomic profile, including proteomics and transcriptomics is required to map differences in carbon metabolism between D. desulfuricans ND132 wild-type and knock-out strains. Therefore EMSL support is critical to determine if changes in central metabolism coordinate to changes in MeHg generation between D. desulfuricans ND132 wild-type and targeted gene deletion strains grown in defined media. RNA-seq analyses will be used to identify differentially expressed genes between biological replicates of the D. desulfuricans ND132 wild-type and mutant strains. Furthermore, MS analyses will provide quantitative comparisons of peptide and protein abundances in D. desulfuricans ND132 wild-type and mutant strain cell cultures. EMSL support will allow us to observe physiological differences between D. desulfuricans ND132 wild-type and knock-out strains and determine if Hg methylation proteins (HgcAB) are involved in carbon metabolism in D. desulfuricans ND132. Understanding the mechanism by which methylation occurs will help to determine the physiological role of this gene pair, including how microbes acquired the ability to methylate Hg. The proposed research will contribute to broader scientific objectives currently funded by the US DOE Office of Science. Outcomes from this work will further our understanding of Hg methylation at the molecular level and therefore our ability to predict MeHg production and accumulation in aquatic ecosystems.
A systems biology approach to identifying the native function of Hg methylation proteins in Desulfovibrio desulfuricans ND132
Monday, October 1, 2018
Oak Ridge National Laboratory
Monday, September 30, 2019