Two Putative c -Type Multiheme Cytochromes Required for the Expression of OmcB, an Outer Membrane Protein Essential for Optimal Fe(III) Reduction in Geobacter sulfurreducens

Abstract

Deletion of two homologousGeobacter sulfurreducens c-type cytochrome genes, omcG and omcH, decreased the rate of Fe(III) reduction and decreased the level of an outer membrane cytochrome critical for Fe(III) reduction, OmcB, without affecting its transcription. Expression of either gene restored Fe(III) reduction and OmcB expression, suggesting functional similarity.

Proteins involved in electron transfer to Fe(III) and Mn(IV) oxides by Geobacter sulfurreducens and Geobacter uraniireducens

“…Strains in which either omcG or omcH was deleted are OmcB-deficient, despite the fact that the omcB gene is still transcribed at wild-type levels (Kim et al, 2006). This result suggests that these two cytochromes may be required either for stabilization of OmcB or for efficient translation of omcB transcripts.…”

“…Despite high levels of expression of omcT, OmcT has been reported to be not abundant in the proteome of Fe(III) oxide-grown cells (Ding et al, 2008). This may be due to the harsh oxalate treatment that was used for protein extraction from Fe(III) oxide, or it may be that translation of omcT mRNA is controlled as is the case for omcB (Kim et al, 2006). Furthermore, gene deletion studies have demonstrated that OmcT is not necessary for Fe(III) or Mn(IV) oxide reduction (Mehta et al, 2005).…”

Transcriptome of Geobacter uraniireducens growing in uranium-contaminated subsurface sediments

“…Gene deletion studies in G. sulfurreducens have shown that OmcB is critical for electron transfer to Fe(III) (Leang et al, 2003;Leang and Lovley, 2005) and that its expression can be directly linked to rates of Fe(III) reduction (Chin et al, 2004). Another gene that was upregulated in sediment-grown cells was the homolog of omcG, which encodes an outer-membrane c-type cytochrome in G. sulfurreducens that plays an important role in the proper expression of omcB (Kim et al, 2006). In addition, the increased expression of a gene that is homologous to the outermembrane c-type cytochrome gene of G. sulfurreducens, omcT, was observed in sediment-grown cells.…”

“…Some of the cytochromes embedded in the outer membrane, such as OmcB (Qian et al, 2007), may also be important for extracellular electron transfer (Leang et al, 2003;Leang and Lovley, 2005), whereas others, such as OmcF, OmcG and OmcH, appear to participate in Fe(III) reduction indirectly by influencing the expression of other outer-surface cytochromes (Kim et al, 2005(Kim et al, , 2006. Studies have also suggested that some of the periplasmic and inner-membrane c-type cytochromes are involved in the transfer of electrons derived from central metabolism to the outer membrane .…”

Harnessing the power of microbial nanowires

“…Genetic studies in the model representative Geobacter sulfurreducens (GS) have provided insights into how the cells assemble the GS pilin into a conductive fibre. However, little is known about how respiratory electrons are discharged through the T4P, partly because mutations that inactivate key electron carriers of the cell envelope, whether the T4P or c‐Cyts, are often pleiotropic (Kim et al ., 2005, 2006; Kim and Lovley, 2008; Cologgi et al ., 2011; Richter et al ., 2012; Steidl et al ., 2016). As a result, compensatory effects are often observed that can mask the true phenotype of the mutants.…”