Anode-assisted electro-fermentation with Bacillus subtilis under oxygen-limited conditions

Area of Science:

• Microbiology
• Biotechnology
• Electrochemistry

Background:

• Bacillus subtilis is a facultative anaerobe, typically using oxygen as its primary electron acceptor.
• In oxygen-deprived conditions, B. subtilis can utilize nitrate or fermentation.
• Anodic electro-fermentation offers an alternative electron sink for microbial metabolism.

Purpose of the Study:

• To optimize industrial bioprocesses by exploring alternative electron acceptors for B. subtilis.
• To investigate the end-product spectrum of B. subtilis with various electron acceptors, including an anode.
• To assess the potential of anode-assisted electro-fermentation for enhanced metabolite production.

Main Methods:

• Cultivation of B. subtilis with oxygen, nitrate, and a poised anode (0.7 V vs. SHE) as sole electron acceptors.
• Anaerobic and limited aeration conditions were tested.
• Quantification of glucose consumption and end-product yields.

Main Results:

• Oxygen is essential for B. subtilis metabolic activity and biomass growth.
• Anaerobic use of nitrate or anode led to cell lysis and limited glucose consumption.
• Anode-assisted electro-fermentation with limited aeration yielded acetoin at 0.78 ± 0.04 mol/mol glucose, double the yield without a poised potential.

Conclusions:

• Oxygen availability critically influences B. subtilis growth, electron acceptor utilization, and metabolite profiles.
• Controlled oxygen limitation allows B. subtilis to direct electrons to nitrate or anode, steering product formation.
• Anode-assisted electro-fermentation demonstrates significant potential for enhancing acetoin production in industrial biotechnology.