title: Global Proteome Response to Deletion of Genes Related to Mercury Methylation and Dissimilatory Metal Reduction Reveals Changes in Respiratory Metabolism in Geobacter sulfurreducens PCA.
abstract: Geobacter sulfurreducens PCA can reduce, sorb, and methylate mercury (Hg); however, the underlying biochemical mechanisms of these processes and interdependent metabolic pathways remain unknown. In this study, shotgun proteomics was used to compare global proteome profiles between wild-type G. sulfurreducens PCA and two mutant strains: a ΔhgcAB mutant, which is deficient in two genes known to be essential for Hg methylation and a ΔomcBESTZ mutant, which is deficient in five outer membrane c-type cytochromes and thus impaired in its ability for dissimilatory metal ion reduction. We were able to delineate the global response of G. sulfurreducens PCA in both mutants and identify cellular networks and metabolic pathways that were affected by the loss of these genes. Deletion of hgcAB increased the relative abundances of proteins implicated in extracellular electron transfer, including most of the c-type cytochromes, PilA-C, and OmpB, and is consistent with a previously observed increase in Hg reduction in the ΔhgcAB mutant. Deletion of omcBESTZ was found to significantly increase relative abundances of various methyltransferases, suggesting that a loss of dissimilatory reduction capacity results in elevated activity among one-carbon (C1) metabolic pathways and thus increased methylation. We show that G. sulfurreducens PCA encodes only the folate branch of the acetyl-CoA pathway, and proteins associated with the folate branch were found at lower abundance in the ΔhgcAB mutant strain than the wild type. This observation supports the hypothesis that the function of HgcA and HgcB is linked to C1 metabolism through the folate branch of the acetyl-CoA pathway by providing methyl groups required for Hg methylation.
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Qian
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Johs
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Chen
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Benjamin F
authors.initials: BF
authors.lastname: Mann
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Xia
authors.initials: X
authors.lastname: Lu
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Abraham
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Hettich
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Baohua
authors.initials: B
authors.lastname: Gu
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D003574:Cytochrome c Group / Q000172:deficiency; D004579:Electron Transport; D017353:Gene Deletion; D045302:Geobacter / Q000235:genetics / Q000378:metabolism*; D008628:Mercury / Q000378:metabolism*; D008670:Metals / Q000378:metabolism*; D008745:Methylation; D010084:Oxidation-Reduction; D020543:Proteome / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D008670:Metals; D020543:Proteome; D000105:Acetyl Coenzyme A; D008628:Mercury
keywords: acetyl-CoA pathway; comparative proteomics; gene deletion; mercury reduction; metabolic processes; methylation