Variation in electrode redox potential selects for different microorganisms under cathodic current flow from...

Area of Science:

• Microbiology
• Environmental Science
• Electrochemistry

Background:

• Extracellular electron transport (EET) is crucial for microbial interaction with insoluble substrates.
• While electron donation is understood, electron reception by microbes remains largely unexplored.
• Marine sediments are complex environments with potential for diverse microbial metabolic activities.

Purpose of the Study:

• Investigate redox potentials supporting microbial electron donation to marine sediment components.
• Characterize microbial communities involved in extracellular electron transfer under varying electrochemical conditions.
• Identify novel microbial groups and metabolic pathways associated with EET in marine environments.

Main Methods:

• Utilized electrochemical techniques by burying working electrodes in sediment microcosms.
• Poised electrodes at seven distinct redox potentials (-300 to -750 mV vs. Ag/AgCl).
• Analyzed electrode biofilms using geochemistry and molecular methods after 2-month incubations.

Main Results:

• Microbial community diversity increased with more negative redox potentials.
• Abundances of known EET-capable bacteria (Alteromonadales, Desulfuromonadales) varied with redox potential.
• Increased abundance of motility and chemotaxis genes suggests adaptation for electrode colonization and utilization.
• Identified known and novel EET-performing groups, including Campylobacterales.

Conclusions:

• Electrochemical methods are effective for enriching and studying EET-capable microbes in marine sediments.
• Insoluble substrate oxidation via EET is a significant, yet under-described, metabolic process in these environments.
• The findings highlight the ecological importance of EET in marine sediment ecosystems.