Visualizing Microbial Indirect Extracellular Electron Transfer.

Area of Science:

• Microbiology
• Biogeochemistry
• Environmental Science

Background:

• Indirect extracellular electron transfer (IEET) is vital for anaerobic microbial respiration and biogeochemical cycling.
• Direct visualization of IEET spatial extent has been a significant limitation in microbial respiration studies.

Purpose of the Study:

• To visually demonstrate and quantify the extent of microbial indirect extracellular electron transfer (IEET) over centimeter distances.
• To investigate the role of various electron shuttles in mediating long-distance IEET.
• To confirm the ubiquity of long-distance IEET across diverse microbial communities.

Main Methods:

• Utilized silver ions (Ag+) as electron traps.
• Employed photothermal imaging of silver nanoparticles (AgNPs) to visualize electron transfer.
• Quantified electron transfer distances mediated by specific microbial strains and electron shuttles.

Main Results:

• Demonstrated microbial electron transfer over centimeter distances, with *Shewanella oneidensis* MR-1 reaching 12.4 ± 0.2 mm.
• Identified both endogenous (e.g., phenazine-1-carboxylic acid, riboflavin) and exogenous (e.g., natural organic matter) molecules as effective electron shuttles.
• Observed long-distance IEET in diverse microbes from aquatic and terrestrial environments, indicating its widespread occurrence.
• Documented impacts of IEET on methanogenesis and iron mineral dissolution.

Conclusions:

• Centimeter-scale IEET is a ubiquitous microbial process with profound impacts on elemental cycling.
• The developed imaging approach provides a robust tool for studying IEET and its biogeochemical consequences.
• Long-distance IEET enhances microbial access to distant electron acceptors and facilitates interspecies electron transfer.