Quantitative Proteomic Analysis of Biological Processes and Responses of the Bacterium Desulfovibrio desulfuricans ND132 upon Deletion of Its Mercury Methylation Genes

Recent studies of microbial mercury (Hg) methylation revealed a key gene pair, hgcAB, which is essential for methylmercury (MeHg) production in the environment. However, many aspects of the mechanism and biological processes underlying Hg methylation, as well as any additional physiological functions of the hgcAB genes, remain unknown. Here, quantitative proteomics are used to identify changes in potential functional processes related to hgcAB gene deletion in the Hg-methylating bacterium Desulfovibrio desulfuricans ND132. Global proteomics analyses indicate that the wild type and ΔhgcAB strains are similar with respect to the whole proteome and the identified number of proteins, but differ significantly in the abundance of specific proteins. The authors observe changes in the abundance of proteins related to the glycolysis pathway and one-carbon metabolism, suggesting that the hgcAB gene pair is linked to carbon metabolism. Unexpectedly, the authors find that the deletion of hgcAB significantly impacts a range of metal transport proteins, specifically membrane efflux pumps such as those associated with heavy metal copper (Cu) export, leading to decreased Cu uptake in the ΔhgcAB mutant. This observation indicates possible linkages between this set of proteins and metal homeostasis in the cell. However, hgcAB gene expression is not induced by Hg, as evidenced by similarly low abundance of HgcA and HgcB proteins in the absence or presence of Hg (500 nm). Taken together, these results suggest an apparent link between HgcAB, one-carbon metabolism, and metal homeostasis, thereby providing insights for further exploration of biochemical mechanisms and biological functions of microbial Hg methylation.