title: Mtr extracellular electron-transfer pathways in Fe(III)-reducing or Fe(II)-oxidizing bacteria: a genomic perspective.
abstract: Originally discovered in the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 (MR-1), key components of the Mtr (i.e. metal-reducing) pathway exist in all strains of metal-reducing Shewanella characterized. The protein components identified to date for the Mtr pathway of MR-1 include four multihaem c-Cyts (c-type cytochromes), CymA, MtrA, MtrC and OmcA, and a porin-like outer membrane protein MtrB. They are strategically positioned along the width of the MR-1 cell envelope to mediate electron transfer from the quinone/quinol pool in the inner membrane to Fe(III)-containing minerals external to the bacterial cells. A survey of microbial genomes has identified homologues of the Mtr pathway in other dissimilatory Fe(III)-reducing bacteria, including Aeromonas hydrophila, Ferrimonas balearica and Rhodoferax ferrireducens, and in the Fe(II)-oxidizing bacteria Dechloromonas aromatica RCB, Gallionella capsiferriformans ES-2 and Sideroxydans lithotrophicus ES-1. The apparent widespread distribution of Mtr pathways in both Fe(III)-reducing and Fe(II)-oxidizing bacteria suggests a bidirectional electron transfer role, and emphasizes the importance of this type of extracellular electron-transfer pathway in microbial redox transformation of iron. The organizational and electron-transfer characteristics of the Mtr pathways may be shared by other pathways used by micro-organisms for exchanging electrons with their extracellular environments.
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, WA 99352, USA. liang.shi@pnnl.gov
authors.forename: Liang
authors.initials: L
authors.lastname: Shi
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Rosso
authors.forename: John M
authors.initials: JM
authors.lastname: Zachara
authors.forename: James K
authors.initials: JK
authors.lastname: Fredrickson
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology; D003574:Cytochrome c Group / Q000235:genetics / Q000502:physiology; D004579:Electron Transport; D005290:Ferric Compounds / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism*; D016680:Genome, Bacterial; D006873:Hydroquinones / Q000378:metabolism; D005810:Multigene Family; D010084:Oxidation-Reduction; D017386:Sequence Homology, Amino Acid; D020592:Shewanella / Q000235:genetics / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D003574:Cytochrome c Group; D005290:Ferric Compounds; D005296:Ferrous Compounds; D006873:Hydroquinones; C017165:cytochrome c(3)