Technical Specifications
NASA Research & Development
NASA Laboratory Research Results
NASA Ames Research Center
Research conducted at NASA Ames has demonstrated Shewanella's viability in simulated space environments, including microgravity conditions and radiation exposure.
International Space Station
Preliminary experiments aboard the ISS have shown that microbial fuel cells can function effectively in space, opening possibilities for long-duration missions.
Mars Simulation Studies
NASA's Mars simulation chambers have tested Shewanella's performance under Martian atmospheric conditions, showing promising results for future Mars missions.
System Specifications
Working Principle: Shewanella bacteria utilize extracellular electron transfer, creating bioelectric circuits. They oxidize organic compounds and transfer electrons to external electrodes, generating direct current.
🔬 Detailed Working Mechanism
1. Substrate Input
Organic matter (lactate, acetate, formate) enters bacterial cell through membrane transporters
2. Metabolic Processing
Intracellular oxidation via quinone pool and cytochrome complexes generates electrons
3. Mtr Pathway
MtrA-MtrB-MtrC protein chain creates conductive bridge from cell to electrode
4. Electron Transfer
Direct contact + flavin shuttles transport electrons to anode surface
5. Current Flow
Electrons flow through external circuit while protons migrate through electrolyte
6. Cathode Reaction
O₂ + 4H⁺ + 4ē → 2H₂O completes the electrochemical circuit
Key Chemical Equation
CH₃CHOHCOO⁻ + 3H₂O → CH₃COO⁻ + HCO₃⁻ + 4H⁺ + 4ē
(Lactate oxidation at anode)
Bioelectrochemical Process
Biowaste to Electricity Conversion:
1. Hydrolysis: Complex organic matter breaks down into simple substrates (lactate, acetate, formate)
2. Oxidation at Anode: Substrates are oxidized, releasing electrons and protons
3. Electron Transport: Intracellular transfer via quinone pool and cytochromes
4. Extracellular Transfer: Mtr pathway proteins (MtrA, MtrB, MtrC) form conductive bridge to anode
5. Current Generation: Electrons flow through external circuit while protons migrate through electrolyte
Key Chemical Reactions:
• Lactate oxidation: CH₃CHOHCOO⁻ + 3H₂O → CH₃COO⁻ + HCO₃⁻ + 4H⁺ + 4ē
• Cathode reaction: O₂ + 4H⁺ + 4ē → 2H₂O
• Overall (acetate): CH₃COO⁻ + 2O₂ → 2CO₂ + H₂O + OH⁻
Performance Metrics:
• Voltage output: 0.5-0.8 V practical range
• Energy yield: ~500 Wh per kg COD at 30% efficiency
• Current density: 0.5-2 A/m² typical range
• Kinetics: Monod-type, influenced by substrate concentration and biomass density
Advanced Mechanisms
Dual-System Electron Transfer:
• Direct Contact Method: Specialized protein complexes form nanoscale biological wires, creating conductive pathways between bacterial cells and external surfaces
• Molecular Shuttle System: Secreted compounds like flavins act as electron taxis, transporting electrical charge from cells to distant acceptors
Environmental Adaptations:
Found ubiquitously in aquatic sediments, soil environments, and extreme habitats like deep-sea vents, these bacteria have evolved sophisticated mechanisms for surviving in oxygen-scarce conditions by "breathing" solid surfaces like metal oxides or electrodes.
Biogeochemical Impact:
Shewanella plays crucial roles in global biogeochemical cycles, transforming iron, manganese, and other metallic compounds in their environment, making them essential for Earth's elemental cycles.