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OmcB, a c-type polyheme cytochrome, involved in Fe(III) reduction in Geobacter sulfurreducens.

ABSTRACT: Microorganisms in the family Geobacteraceae are the predominant Fe(III)-reducing microorganisms in a variety of subsurface environments in which Fe(III) reduction is an important process, but little is known about the mechanisms for electron transport to Fe(III) in these organisms. The Geobacter sulfurreducens genome was found to contain a 10-kb chromosomal duplication consisting of two tandem three-gene clusters. The last genes of the two clusters, designated omcB and omcC, encode putative outer membrane polyheme c-type cytochromes which are 79% identical. The role of the omcB and omcC genes in Fe(III) reduction in G. sulfurreducens was investigated. OmcB and OmcC were both expressed during growth with acetate as the electron donor and either fumarate or Fe(III) as the electron acceptor. OmcB was ca. twofold more abundant under both conditions. Disrupting omcB or omcC by gene replacement had no impact on growth with fumarate. However, the OmcB-deficient mutant was greatly impaired in its ability to reduce Fe(III) both in cell suspensions and under growth conditions. In contrast, the ability of the OmcC-deficient mutant to reduce Fe(III) was similar to that of the wild type. When omcB was reintroduced into the OmcB-deficient mutant, the capacity for Fe(III) reduction was restored in proportion to the level of OmcB production. These results indicate that OmcB, but not OmcC, has a major role in electron transport to Fe(III) and suggest that electron transport to the outer membrane is an important feature in Fe(III) reduction in this organism.

SUBMITTER: Leang C

PROVIDER: S-EPMC151516 | biostudies-literature | 2003 Apr

REPOSITORIES: biostudies-literature

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OmcB, a c-type polyheme cytochrome, involved in Fe(III) reduction in Geobacter sulfurreducens.

Leang Ching C Coppi M V MV Lovley D R DR

Journal of bacteriology 20030401 7

Microorganisms in the family Geobacteraceae are the predominant Fe(III)-reducing microorganisms in a variety of subsurface environments in which Fe(III) reduction is an important process, but little is known about the mechanisms for electron transport to Fe(III) in these organisms. The Geobacter sulfurreducens genome was found to contain a 10-kb chromosomal duplication consisting of two tandem three-gene clusters. The last genes of the two clusters, designated omcB and omcC, encode putative oute ...[more]

PMID: 12644478

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Project description:The conductive pili of Geobacter sulfurreducens are essential for optimal extracellular electron transfer to Fe(III) and long-range electron transport through current-producing biofilms. The KN400 strain of G. sulfurreducens reduces poorly crystalline Fe(III) oxide more rapidly than the more extensively studied DL-1 strain. Deletion of the gene for PilA, the structural pilin protein, in strain KN400 inhibited Fe(III) oxide reduction. However, slow rates of Fe(III) reduction were detected after extended (> 30 days) incubation in the presence of Fe(III) oxide. After seven consecutive transfers the PilA-deficient strain adapted to reduce Fe(III) oxide as fast as the wild type. Microarray, proteomic, and gene deletion studies indicated that this adaptation was associated with greater production of the c-type cytochrome PgcA, which was released into the culture medium. It is proposed that the extracellular cytochrome acts as an electron shuttle, promoting electron transfer from the outer cell surface to Fe(III) oxides. The adapted PilA-deficient strain competed well with the wild-type strain when both were grown together on Fe(III) oxide. However, when 50% of the culture medium was replaced with fresh medium every three days, the wild-type strain out-competed the adapted strain. A possible explanation for this is that the necessity to produce additional PgcA, to replace the PgcA continually removed, put the adapted strain at a competitive disadvantage, similar to the apparent selection against electron-shuttling producing Fe(III) reducers in most soils and sediments. Despite increased extracellular cytochrome production, the adapted PilA-deficient strain produced low levels of current; consistent with the concept that long-range electron transport through G. sulfurreducens biofilms cannot be achieved without PilA-pili. An eight-chip study using total RNA recovered from four separate cultures of Geobacter sulfurreducens JS-1 (experimental condition) or Geobacter sulfurreducens KN400 (control condition) grown with acetate (10mM)-Fe(III) oxide (100 mmol l-1) exponential growth. Each chip measures the expression level of 3,328 genes from Geobacter sulfurreducens KN400 with nine 45-60-mer probe pairs (PM/MM) per gene, with three-fold technical redundancy.

Dataset Information

OmcB, a c-type polyheme cytochrome, involved in Fe(III) reduction in Geobacter sulfurreducens.

Publications

OmcB, a c-type polyheme cytochrome, involved in Fe(III) reduction in Geobacter sulfurreducens.

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