Extracellular electron transfer via microbial nanowires.

Area of Science:

• Microbiology
• Geochemistry
• Biophysics

Background:

• Extracellular electron transfer is crucial for microbial organic matter degradation and nutrient cycling.
• Outer-membrane c-type cytochromes have been the primary focus for microbial Fe(iii) reduction.
• Some Fe(iii)-reducing microbes, like Geobacter species, lack c-cytochromes, necessitating alternative electron transfer mechanisms.

Purpose of the Study:

• To investigate the role of pili in the extracellular electron transfer of Geobacter sulfurreducens to Fe(iii) oxides.
• To determine if pili are essential for Fe(iii) oxide reduction in Geobacter species.
• To explore the conductive properties of Geobacter sulfurreducens pili.

Main Methods:

• Construction and analysis of a pilus-deficient mutant of Geobacter sulfurreducens.
• Assessment of Fe(iii) oxide reduction capabilities in wild-type and mutant strains.
• Utilizing conducting-probe atomic force microscopy to evaluate pili conductivity.

Main Results:

• The pilus-deficient mutant of Geobacter sulfurreducens lost the ability to reduce Fe(iii) oxides.
• The mutant strain retained the ability to attach to Fe(iii) oxides, indicating pili are not solely for adhesion.
• Conducting-probe atomic force microscopy demonstrated that the pili are highly conductive.

Conclusions:

• Geobacter sulfurreducens pili function as biological nanowires, facilitating electron transfer from the cell to extracellular Fe(iii) oxides.
• Pili-mediated electron transfer represents a novel mechanism for microbial respiration and biogeochemical cycling.
• The conductive nature of pili opens avenues for bioengineering novel conductive biomaterials and understanding unique cell-surface interactions.