Microbial Electrosynthesis for Organic Acids

 Introduction

Microbial electrosynthesis (MES) is an innovative biotechnological process that uses electrically active microbes to convert CO₂ or other carbon sources into value-added chemicals, using electrodes as electron donors or acceptors. One of the most promising applications of MES is the biosynthesis of organic acids, such as acetic acid, formic acid, succinic acid, and butyric acid, from renewable electricity and CO₂.

Unlike traditional fermentation, MES offers precise control over redox balance, the ability to integrate with renewable energy sources, and a carbon-negative pathway for producing platform chemicals. It combines bioelectrochemistry, synthetic biology, and microbial metabolism—making it a frontier technology in carbon capture and biomanufacturing.

What Products Are Produced?

• Acetic acid – Solvents, food preservatives, plastics
• Formic acid – Hydrogen storage, leather, rubber chemicals
• Succinic acid – Bioplastics (PBS), food additives
• Butyric acid – Pharmaceuticals, plastics, perfumes
• Propionic acid, caproic acid – Food preservation, plasticizers

Pathways and Production Methods

1. CO₂ Fixation via Wood–Ljungdahl Pathway

• CO₂ + 8H⁺ + 8e⁻ → Acetyl-CoA → Acetic acid
• Used by acetogens (Clostridium ljungdahlii, Sporomusa ovata)
• Electrons provided from cathode or H₂ mediated transfer

2. Reverse β-Oxidation Pathway

• Produces butyrate, caproate via chain elongation of acetate
• Mixed cultures with electron flow from cathode stimulate this pathway
• Used in co-electrosynthesis setups

3. CO₂ + Electrons → Formate via Electroactive Bacteria

• Shewanella or Geobacter used in direct extracellular electron transfer (DEET)
• Synthetic biology used to insert organic acid pathways

4. Syngas Integration in MES

• CO or H₂ used along with MES to boost yields
• Enables syngas-to-organic acids via electrobiocatalysis

Catalysts and Key Tools Used

 Electroactive Microbes:

• • Clostridium ljungdahlii, Sporomusa ovata, Geobacter sulfurreducens, Shewanella oneidensis

 Electron Delivery Systems:

• • Cathodes (graphite, carbon cloth, stainless steel mesh)
  • H₂-evolving surfaces for indirect electron mediation
  • Redox mediators (methyl viologen, neutral red)

 Synthetic Biology Enhancements:

• • Insertion of acid-producing operons
  • CRISPR-Cas systems for redox tuning
  • Promoter engineering for current-dependent gene expression

  Reactor Types:

• • Two-chamber MES reactors (anode/cathode separated)
  • Bioelectrochemical systems with inline pH and voltage control

Case Study: Acetate Production from CO₂ via MES by Sparacino-Watkins et al.

Highlights

• Used Sporomusa ovata with graphite cathode to convert CO₂ → acetate
• Achieved 90% faradaic efficiency for acetic acid production
• Demonstrated stable performance over 120+ days
• Biofilm formation key to electrochemical interface stability

Timeline

• 2013 – First demonstration of CO₂-to-acetate MES at lab scale
• 2016 – Continuous flow MES for acetate developed
• 2020 – Hybrid MES integrated with solar panels tested
• 2023 – MES acetate tested in bioplastic precursor applications

Global and Indian Startups Working in This Area

Global

• LanzaTech – Exploring MES for syngas and CO₂ valorization
• Twelve (USA) – Developing CO₂-to-chemicals via electro-biological platforms
• ENGIE & BioElectrochemistry consortium (EU) – Working on MES at scale
• VoltCarbon (Canada) – CO₂ to acetate and formate MES reactors

India

• IISc Bangalore – MES systems for acetic and butyric acid production
• IIT Madras – CO₂ electro-bioreactors with Geobacter spp.
• CSIR-IICT Hyderabad – Exploring hybrid MES-biorefinery systems
• Startups in BIRAC portfolio – Prototyping MES devices for organic acid production

Market and Demand

The global organic acids market is valued at USD 12.8 billion (2023) and is expected to grow to USD 18.2 billion by 2030, at a CAGR of ~5.1%. MES can play a disruptive role in the green segment, enabling carbon-neutral or negative manufacturing.

Major End-Use Segments:

• Food preservatives – Acetic, propionic, lactic acids
• Bioplastics and green solvents – Succinic and lactic acids
• Pharmaceuticals and cosmetics – Butyric, valeric acids
• Agrochemicals and tanning – Formic acid

Key Growth Drivers

• Need for low-carbon chemical manufacturing
• Surplus of CO₂ and renewable electricity in industrial settings
• Regulatory push for biobased acid production (EU, US)
• Integration with solar/wind for carbon utilization
• Development of stable electroactive microbial consortia

Challenges to Address

• Low production rates compared to traditional fermentation
• Electrode fouling and biofilm control
• Limited scalability and techno-economic validation
• Need for robust microbe-electrode interfaces
• In India: Cost barriers for high-performance bioelectrochemical setups

Progress Indicators

• 2012–2015 – Lab-scale acetate and formate MES demonstrations
• 2018 – Microbial pathways optimized with CRISPR tools
• 2021 – Acetate and succinate MES integrated with solar panels
• 2023 – Pilot MES systems for food-grade acetic acid begin
• 2024 – MES-acid integration in Indian biorefinery pilots initiated

MES for organic acids is at TRL 4–6 globally, with pilot and demo units operational in North America and Europe. In India, systems remain at TRL 3–4, with academic institutions and startups leading early development.

Conclusion

Microbial electrosynthesis (MES) offers a bold new approach to producing organic acids in a sustainable, electricity-driven bioprocess, using CO₂ as feedstock and electrons as energy. Though still emerging, it shows immense potential for decarbonizing chemical production, especially when integrated with renewable energy systems.

As India builds capabilities in bioelectrochemical platforms and synthetic biology, MES could become a core component of next-generation biorefineries, producing low-carbon organic acids for food, plastics, and fuels.

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