Microbial nanowires: type IV pili or cytochrome filaments?

Area of Science:

• Microbiology
• Biophysics
• Nanotechnology

Background:

• Extracellular electron transport via filaments in anaerobic bacteria is a key area of research.
• Geobacter sulfurreducens serves as a model organism for studying these phenomena.
• Potential applications include bioremediation, energy generation, and bio-based electronics.

Purpose of the Study:

• To re-evaluate the structural basis of long-range electron transport in Geobacter sulfurreducens.
• To determine the true composition of conductive extracellular filaments previously identified as type IV pili.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine high-resolution atomic structures.
• Structural analysis of type IV pili (T4P) from G. sulfurreducens.
• Investigation of alternative structures for conductive extracellular filaments.

Main Results:

• High-resolution cryo-EM structures of T4P from G. sulfurreducens are incompatible with proposed electron conduction models.
• Conductive filaments previously misidentified as T4P are actually polymerized cytochromes or extracellular DNA.
• Polymerized cytochromes feature stacked heme groups forming a conductive wire.

Conclusions:

• The structural data refutes the role of T4P in the observed extracellular electron transport.
• Polymerized cytochromes represent a novel mechanism for long-range electron transport in bacteria.
• These findings suggest that conductive cytochrome polymers may be widespread among anaerobic organisms.