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Title: Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1

Abstract

In the absence of O2 and other electron acceptors, the Gram-negative bacterium Shewanella oneidensis MR-1 can use ferric [Fe(III)] (oxy)(hydr)oxide minerals as the terminal electron acceptors for anaerobic respiration. At circumneutral pH and in the absence of strong complexing ligands, Fe(III) oxides are relatively insoluble and thus are external to the bacterial cells. S. oneidensis MR-1 and related strains of metal-reducing Shewanella have evolved the machinery (i.e., metal-reducing or Mtr pathway) for transferring electrons from the inner-membrane, through the periplasm and across the outer-membrane to the surface of extracellular Fe(III) oxides. The protein components identified to date for the Mtr pathway include CymA, MtrA, MtrB, MtrC and OmcA. CymA is an inner-membrane tetraheme c-type cytochrome (c-Cyt) that belongs to the NapC/NrfH family of quinol dehydrogenases. It is proposed that CymA oxidizes the quinol in the inner-membrane and transfers the released electrons to redox proteins in the periplasm. Although the periplasmic proteins receiving electrons from CymA during Fe(III) oxidation have not been identified, they are believed to relay the electrons in the periplasm to MtrA. A decaheme c-Cyt, MtrA is thought to be embedded in the trans outer-membrane and porin-like protein MtrB. Together, MtrAB deliver the electrons through the outer-membrane tomore » the MtrC and OmcA on the outmost bacterial surface. MtrC and OmcA are the outer-membrane decaheme c-Cyts that are translocated across the outer-membrane by the bacterial type II secretion system. Functioning as terminal reductases, MtrC and OmcA can bind the surface of Fe(III) oxides and transfer electrons directly to these minerals via their solvent-exposed hemes. To increase their reaction rates, MtrC and OmcA can use the flavins secreted by S. oneidensis MR-1 cells as diffusible co-factors for reduction of Fe(III) oxides. Because of their extracellular location and broad redox potentials, MtrC and OmcA can also serve as the terminal reductases for soluble forms of Fe(III). Although our understanding of the Mtr pathway is still far from complete, it is the best characterized microbial pathway used for extracellular electron exchange. Characterizations of the Mtr pathway have made significant contributions to the molecular understanding of microbial reduction of Fe(III) oxides.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1036070
Report Number(s):
PNNL-SA-83454
KP1702030; TRN: US201205%%587
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Frontiers in Microbiological Chemistry, 3:Article No. 50
Additional Journal Information:
Journal Volume: 3
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 60 APPLIED LIFE SCIENCES; BINDING ENERGY; CYTOCHROMES; ELECTRON EXCHANGE; ELECTRONS; ISOALLOXAZINES; MACHINERY; OXIDATION; OXIDES; OXIDOREDUCTASES; PROTEINS; REACTION KINETICS; REDOX POTENTIAL; RESPIRATION; SECRETION; STRAINS; VALENCE; Dissimilatory Fe(III) oxide reduction; Shewanella oneidensis MR-1; extracellular electron transfer pathway; c-type cytochromes with multiple hemes; molecular biology

Citation Formats

Shi, Liang, Rosso, Kevin M, Clarke, Thomas A, Richardson, David J, Zachara, John M, and Fredrickson, Jim K. Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1. United States: N. p., 2012. Web. doi:10.3389/fmicb.2012.00050.
Shi, Liang, Rosso, Kevin M, Clarke, Thomas A, Richardson, David J, Zachara, John M, & Fredrickson, Jim K. Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1. United States. doi:10.3389/fmicb.2012.00050.
Shi, Liang, Rosso, Kevin M, Clarke, Thomas A, Richardson, David J, Zachara, John M, and Fredrickson, Jim K. Wed . "Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1". United States. doi:10.3389/fmicb.2012.00050.
@article{osti_1036070,
title = {Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1},
author = {Shi, Liang and Rosso, Kevin M and Clarke, Thomas A and Richardson, David J and Zachara, John M and Fredrickson, Jim K},
abstractNote = {In the absence of O2 and other electron acceptors, the Gram-negative bacterium Shewanella oneidensis MR-1 can use ferric [Fe(III)] (oxy)(hydr)oxide minerals as the terminal electron acceptors for anaerobic respiration. At circumneutral pH and in the absence of strong complexing ligands, Fe(III) oxides are relatively insoluble and thus are external to the bacterial cells. S. oneidensis MR-1 and related strains of metal-reducing Shewanella have evolved the machinery (i.e., metal-reducing or Mtr pathway) for transferring electrons from the inner-membrane, through the periplasm and across the outer-membrane to the surface of extracellular Fe(III) oxides. The protein components identified to date for the Mtr pathway include CymA, MtrA, MtrB, MtrC and OmcA. CymA is an inner-membrane tetraheme c-type cytochrome (c-Cyt) that belongs to the NapC/NrfH family of quinol dehydrogenases. It is proposed that CymA oxidizes the quinol in the inner-membrane and transfers the released electrons to redox proteins in the periplasm. Although the periplasmic proteins receiving electrons from CymA during Fe(III) oxidation have not been identified, they are believed to relay the electrons in the periplasm to MtrA. A decaheme c-Cyt, MtrA is thought to be embedded in the trans outer-membrane and porin-like protein MtrB. Together, MtrAB deliver the electrons through the outer-membrane to the MtrC and OmcA on the outmost bacterial surface. MtrC and OmcA are the outer-membrane decaheme c-Cyts that are translocated across the outer-membrane by the bacterial type II secretion system. Functioning as terminal reductases, MtrC and OmcA can bind the surface of Fe(III) oxides and transfer electrons directly to these minerals via their solvent-exposed hemes. To increase their reaction rates, MtrC and OmcA can use the flavins secreted by S. oneidensis MR-1 cells as diffusible co-factors for reduction of Fe(III) oxides. Because of their extracellular location and broad redox potentials, MtrC and OmcA can also serve as the terminal reductases for soluble forms of Fe(III). Although our understanding of the Mtr pathway is still far from complete, it is the best characterized microbial pathway used for extracellular electron exchange. Characterizations of the Mtr pathway have made significant contributions to the molecular understanding of microbial reduction of Fe(III) oxides.},
doi = {10.3389/fmicb.2012.00050},
journal = {Frontiers in Microbiological Chemistry, 3:Article No. 50},
number = ,
volume = 3,
place = {United States},
year = {2012},
month = {2}
}