Evidence for direct electron transfer by a gram-positive bacterium isolated from a microbial fuel cell

Area of Science:

• Microbiology
• Bioenergetics
• Electrochemistry

Background:

• Extracellular electron transfer (EET) mechanisms in Gram-positive bacteria are poorly understood.
• These bacteria are crucial for iron redox cycles and bioenergy production.
• Thermincola potens strain JR was isolated from a microbial fuel cell anode.

Purpose of the Study:

• Investigate the physiological, genetic, and biochemical mechanisms of EET by Thermincola potens strain JR.
• Determine how Gram-positive bacteria interact with insoluble electron acceptors.
• Elucidate the role of specific cellular components in charge transfer.

Main Methods:

• Physiological experiments and cyclic voltammetry to assess electron transfer.
• Confocal microscopy to analyze biofilm structure and cell viability.
• Cryo-electron microscopy to visualize cellular structures.
• Genomic analysis to identify relevant genes.

Main Results:

• No evidence of secreted soluble redox-active components was found.
• Highly stratified biofilms showed preferential viability in cells contacting the electrode.
• Biofilm thickness did not correlate with power production, indicating surface-contact cells are key.
• Cryo-EM supported contact-dependent electron transfer across the 37-nm cell envelope.
• Physiological and genomic data suggest c-type cytochromes are involved in charge transfer.

Conclusions:

• Thermincola potens strain JR utilizes contact-dependent extracellular electron transfer.
• Electron transfer occurs across the cell envelope to the cell surface.
• C-type cytochromes are implicated in facilitating charge transfer across the Gram-positive cell envelope during metal reduction.