Revealing extracellular electron transfer mediated parasitism: energetic considerations

Area of Science:

• Microbiology
• Biochemistry
• Bioenergetics

Background:

• Extracellular electron transfer (EET) facilitates energy exchange between microorganisms or microbes and electrodes.
• Interspecies EET (IET) has primarily been studied for syntrophic interactions.
• This study examines fermentative bacteria utilizing extracellular electrons.

Purpose of the Study:

• To investigate the energetic implications of fermentative bacteria accepting extracellular electrons.
• To re-evaluate literature data on decreased microbial biomass yields in the context of EET.
• To explore the potential of IET-mediated parasitism for optimizing fermentation.

Main Methods:

• Thermodynamical analysis using metabolic energy balances.
• Re-analysis of existing experimental data from scientific literature.
• Case studies including Propionibacterium freudenreichii and Clostridium pasteurianum.

Main Results:

• Decreased cell biomass yields in fermentative electron-accepting species can be explained by EET energetics, indicating parasitism.
• The growth yield decrease in Propionibacterium freudenreichii (-14%) was fully explained by EET at -0.12 ± 0.01 V vs SHE.
• Biomass reduction in Clostridium pasteurianum (-33% to -38%) involved both EET energetics and biological regulations.

Conclusions:

• IET-mediated parasitism and electro-fermentation offer strategies to optimize carbon flux by reducing biomass production.
• Reduced bacterial biomass is coupled with increased production of reduced compounds.
• EET energetics provides a key framework for understanding these microbial interactions and optimizing industrial fermentation.