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Title: Identification and Characterization of MtoA: a Decaheme c-Type Cytochrome of the Neutrophilic Fe(II)-oxidizing Bacterium Sideroxydans lithotrophicus ES-1

Abstract

The Gram-negative bacterium Sideroxydans lithotrophicus ES-1 (ES-1) grows on FeCO{sub 3} or FeS at oxic-anoxic interfaces at circumneutral pH, and the ES-1-mediated Fe(II) oxidation occurs extracellularly. However, the molecular mechanisms underlying ES-1's ability to oxidize Fe(II) remain unknown. Survey of the ES-1 genome for the genes known for microbial extracellular Fe(II) oxidation revealed that it contained a three-gene cluster encoding an MtrA homologue, an MtrB homologue and a CymA homologue. The homologues of MtrA, MtrB and/or CymA were previously shown to be involved in extracellular Fe(II) oxidation by Rhodopseudomonas palustris TIE-1 and in extracellular Fe(III) reduction by Shewanella oneidensis MR-1 (MR-1). To distinguish them from those found in MR-1, the identified homologues were named MtoAB and CymA{sub ES-1}, respectively. The gene for MtoA was cloned, and cloned mtoA partially complemented an MR-1 mutant without MtrA in ferrihydrite reduction. Following overexpression in MR-1 cells, recombinant MtoA was purified. Characterization of purified MtoA showed that it was a decaheme c-type cytochrome and oxidized soluble Fe(II). Oxidation of Fe(II) by MtoA was pH- and Fe(II)-complexing ligand-dependent. Under conditions tested, MtoA oxidized Fe(II) at pH ranging from 7-9, and optimal oxidation occurred at pH 9, possibly because of the attendant net increase of [Fe(OH){supmore » +}] at higher pH. MtoA oxidized Fe(II) complexed with different ligands at different rates. The reaction rates followed the order Fe(II)Cl2 > Fe(II)-citrate > Fe(III)-NTA > Fe(II)-EDTA with the second-order rate constants ranging from 5.5 x 10{sup -3} {micro}M{sup -1}s{sup -1} for oxidation of Fe(II)Cl{sub 2} to 1.0 x 10{sup -3} {micro}M{sup -1}s{sup -1} for oxidation of Fe(II)-EDTA. Thermodynamic modeling shows that redox reaction rate differences for the different Fe(II)-complexes correlated with estimated reaction-free energies. Collectively, these results suggest that MtoA is a functional Fe(II)-oxidizing protein that, by working in concert with MtoB and CymAES 1, may oxidize the Fe(II) on the bacterial surface and transfer released electrons across the bacterial cell envelope to the quinone pool in the inner membrane during extracellular Fe(II) oxidation by ES-1.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1036063
Report Number(s):
PNNL-SA-83499
KP1702030; TRN: US201205%%580
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Frontiers in Microbiological Chemistry
Additional Journal Information:
Journal Volume: 3
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 60 APPLIED LIFE SCIENCES; BENZOQUINONES; CYTOCHROMES; ELECTRONS; FUNCTIONALS; GENES; MEMBRANES; MUTANTS; OXIDATION; PROTEINS; REACTION KINETICS; REDOX REACTIONS; RHODOPSEUDOMONAS; SIMULATION; THERMODYNAMICS; Sideroxydans lithotrophicus ES-1; extracellular Fe(II) oxidation; decaheme c-type cytochrome MtoA; pH-dependent; ligand complexation

Citation Formats

Liu, Juan, Wang, Zheming, Belchik, Sara M, Edwards, Marcus, Liu, Chongxuan, Kennedy, David W, Merkley, Eric D, Lipton, Mary S, Butt, Julea N, Richardson, David, Zachara, John M, Fredrickson, Jim K, Rosso, Kevin M, and Shi, Liang. Identification and Characterization of MtoA: a Decaheme c-Type Cytochrome of the Neutrophilic Fe(II)-oxidizing Bacterium Sideroxydans lithotrophicus ES-1. United States: N. p., 2012. Web. doi:10.3389/fmicb.2012.00037.
Liu, Juan, Wang, Zheming, Belchik, Sara M, Edwards, Marcus, Liu, Chongxuan, Kennedy, David W, Merkley, Eric D, Lipton, Mary S, Butt, Julea N, Richardson, David, Zachara, John M, Fredrickson, Jim K, Rosso, Kevin M, & Shi, Liang. Identification and Characterization of MtoA: a Decaheme c-Type Cytochrome of the Neutrophilic Fe(II)-oxidizing Bacterium Sideroxydans lithotrophicus ES-1. United States. doi:10.3389/fmicb.2012.00037.
Liu, Juan, Wang, Zheming, Belchik, Sara M, Edwards, Marcus, Liu, Chongxuan, Kennedy, David W, Merkley, Eric D, Lipton, Mary S, Butt, Julea N, Richardson, David, Zachara, John M, Fredrickson, Jim K, Rosso, Kevin M, and Shi, Liang. Wed . "Identification and Characterization of MtoA: a Decaheme c-Type Cytochrome of the Neutrophilic Fe(II)-oxidizing Bacterium Sideroxydans lithotrophicus ES-1". United States. doi:10.3389/fmicb.2012.00037.
@article{osti_1036063,
title = {Identification and Characterization of MtoA: a Decaheme c-Type Cytochrome of the Neutrophilic Fe(II)-oxidizing Bacterium Sideroxydans lithotrophicus ES-1},
author = {Liu, Juan and Wang, Zheming and Belchik, Sara M and Edwards, Marcus and Liu, Chongxuan and Kennedy, David W and Merkley, Eric D and Lipton, Mary S and Butt, Julea N and Richardson, David and Zachara, John M and Fredrickson, Jim K and Rosso, Kevin M and Shi, Liang},
abstractNote = {The Gram-negative bacterium Sideroxydans lithotrophicus ES-1 (ES-1) grows on FeCO{sub 3} or FeS at oxic-anoxic interfaces at circumneutral pH, and the ES-1-mediated Fe(II) oxidation occurs extracellularly. However, the molecular mechanisms underlying ES-1's ability to oxidize Fe(II) remain unknown. Survey of the ES-1 genome for the genes known for microbial extracellular Fe(II) oxidation revealed that it contained a three-gene cluster encoding an MtrA homologue, an MtrB homologue and a CymA homologue. The homologues of MtrA, MtrB and/or CymA were previously shown to be involved in extracellular Fe(II) oxidation by Rhodopseudomonas palustris TIE-1 and in extracellular Fe(III) reduction by Shewanella oneidensis MR-1 (MR-1). To distinguish them from those found in MR-1, the identified homologues were named MtoAB and CymA{sub ES-1}, respectively. The gene for MtoA was cloned, and cloned mtoA partially complemented an MR-1 mutant without MtrA in ferrihydrite reduction. Following overexpression in MR-1 cells, recombinant MtoA was purified. Characterization of purified MtoA showed that it was a decaheme c-type cytochrome and oxidized soluble Fe(II). Oxidation of Fe(II) by MtoA was pH- and Fe(II)-complexing ligand-dependent. Under conditions tested, MtoA oxidized Fe(II) at pH ranging from 7-9, and optimal oxidation occurred at pH 9, possibly because of the attendant net increase of [Fe(OH){sup +}] at higher pH. MtoA oxidized Fe(II) complexed with different ligands at different rates. The reaction rates followed the order Fe(II)Cl2 > Fe(II)-citrate > Fe(III)-NTA > Fe(II)-EDTA with the second-order rate constants ranging from 5.5 x 10{sup -3} {micro}M{sup -1}s{sup -1} for oxidation of Fe(II)Cl{sub 2} to 1.0 x 10{sup -3} {micro}M{sup -1}s{sup -1} for oxidation of Fe(II)-EDTA. Thermodynamic modeling shows that redox reaction rate differences for the different Fe(II)-complexes correlated with estimated reaction-free energies. Collectively, these results suggest that MtoA is a functional Fe(II)-oxidizing protein that, by working in concert with MtoB and CymAES 1, may oxidize the Fe(II) on the bacterial surface and transfer released electrons across the bacterial cell envelope to the quinone pool in the inner membrane during extracellular Fe(II) oxidation by ES-1.},
doi = {10.3389/fmicb.2012.00037},
journal = {Frontiers in Microbiological Chemistry},
number = ,
volume = 3,
place = {United States},
year = {2012},
month = {2}
}