Outer cell surface components essential for Fe(III) oxide reduction by Geobacter metallireducens.

Area of Science:

• Microbiology
• Geochemistry
• Environmental Science

Background:

• Geobacter species are crucial for Fe(III) reduction in soils and sediments.
• While Fe(III) reduction mechanisms are known for G. sulfurreducens, key outer surface proteins like c-type cytochromes differ among Geobacter species.

Purpose of the Study:

• To identify cellular components critical for Fe(III) oxide reduction in Geobacter metallireducens.
• To compare extracellular electron transfer mechanisms between G. metallireducens and G. sulfurreducens.

Main Methods:

• Whole-genome microarrays were used to compare gene transcript abundance in cells grown on Fe(III) oxide versus soluble Fe(III) citrate.
• Outer-surface c-type cytochromes were identified.
• Deletion mutants of specific c-type cytochrome genes were analyzed for their Fe(III) oxide reduction capacity.

Main Results:

• Six c-type cytochrome genes, when deleted, abolished Fe(III) oxide reduction in G. metallireducens.
• Some essential c-type cytochromes in G. metallireducens lack functional importance in G. sulfurreducens.
• Other essential genes included those for an NHL repeat-containing protein and pili glycosylation.
• Genes for motility, chemotaxis, and pili showed higher expression during Fe(III) oxide growth.

Conclusions:

• Extracellular electron transfer mechanisms show similarities between G. metallireducens and G. sulfurreducens.
• The specific outer-surface c-type cytochromes involved in Fe(III) oxide reduction are distinct between these two species.
• Motility and pili-associated functions are important for Fe(III) oxide reduction in G. metallireducens.