Microbe discovery holds promise for sustainable biotechnology

“Chen et al. report the discovery of microorganisms that use energy derived from sulfide oxidation and iron-oxide reduction to drive carbon fixation (S.-C. Chen et al. Nature https://doi.org/g9zqq2; 2025).

 

In our view, these microbes (known as MISO organisms [1]) could be used for sustainable biotechnology.

 

Current bioprocessing systems rely on costly organic raw materials, such as sugars. But because of their unusual metabolisms, MISO organisms do not require such materials. They could make products such as biofuels, bioplastics and pharmaceuticals in a carbon-neutral way by fixing, rather than producing, carbon dioxide.

 

To harness MISO organisms for biotechnology, next steps should include developing efficient ways to manipulate the genes of these species, optimizing cultivation protocols for biotechnological applications and engineering enhanced metabolic capabilities for industrial-scale production (J. M. López et al. Nature Rev. Microbiol. 20, 35–48; 2022). Addressing these challenges requires collaboration between synthetic biologists, metabolic engineers and microbiologists. Success could lead to sustainable biotechnological platforms that simultaneously achieve waste repurposing, carbon neutrality and chemical production.” [2]

 

1. MISO bacteria (Microbial Iron-oxide reduction and Sulfide Oxidation) are a newly discovered group of microorganisms, including species like Desulfurivibrio alkaliphilus, that "breathe" iron(III) oxide minerals while oxidizing toxic sulfide to produce energy. Found in marine sediments and wetlands, they fix CO2 for growth, detoxify sulfide, and play a key role in global carbon and sulfur cycles. 

  

Key details about MISO bacteria: 

• Metabolism: These bacteria utilize a newly discovered metabolism that couples the reduction of solid iron(III) oxide with the oxidation of sulfide to sulfate, acting as a faster alternative to chemical reactions.
• Carbon Fixation: They are chemolithoautotrophs, using the energy from this redox reaction to fix inorganic carbon (CO2) into biomass.

 

• Environmental Impact: MISO bacteria are found in marine sediments and wetlands, where they help prevent the expansion of oxygen-free "dead zones" by removing toxic hydrogen sulfide.

 

• Significance: This metabolic pathway is linked to the reduction of iron, and studies suggest it is used by diverse prokaryotic phyla.
• Biotechnology: Due to their unique metabolic capabilities, these microorganisms hold promise for sustainable, carbon-neutral biotechnology. 

Desulfurivibrio alkaliphilus has been specifically identified as a bacterium capable of reducing ferrihydrite while oxidizing sulfide, using a pathway that involves multi-heme c-type cytochromes. 

How could production process be organised using MISO organisms? Compare the price of final product in contemporary biotech and MISO-based one.

 

Production processes using Microbial Iron-oxide reduction and Sulfide Oxidation (MISO) represent an emerging, eco-friendly biotechnology designed to remove toxic sulfides, treat wastewater, and potentially produce biochemicals by coupling sulfur oxidation with iron reduction. This process, pioneered by researchers studying organisms like Desulfurivibrio alkaliphilus, uses Fe(III) oxides ("rust") as electron acceptors to convert sulfide directly to sulfate. 

 

Organization of a MISO-Based Production Process 

 

A production process based on MISO can be designed as an engineered, high-efficiency, anaerobic or facultative anaerobic system. 

• Substrate Feedstock: The process requires a source of reduced sulfur compounds (e.g., hydrogen sulfide or FeS) and iron(III) oxides.

 

• Wastewater or sludge from industrial, sewage, or mining sources (acid mine drainage) can act as an inexpensive feedstock.

 

• Bioreactor Design:
• Solid-State/Column Reactor: Inoculated iron-oxide coated sand or solid media in packed-bed reactors can facilitate the growth of MISO bacteria.
• Packed-Bed or Upflow Anaerobic Sludge Blanket (UASB) Reactors: These are suitable for treating liquid waste streams containing dissolved sulfide, with iron oxides provided as solid particles.
• Key Microbial Agents: Desulfurivibrio alkaliphilus and similar microorganisms that use extracellular electron transfer (EET) to connect sulfur oxidation to iron reduction.
• Process Conditions: The reaction runs in anoxic conditions, often utilizing iron-oxide nanoparticles for faster sulfide oxidation.
• Key Operations:

1.                  Sulfide Control: The bacteria convert toxic sulfide to sulfate, reducing environmental contamination.

2.                  Iron Recycling: Reduced Fe(II) can be re-oxidized to Fe(III) (e.g., via chemical or biological aerobic processes) to enable a circular process.

3.                  Product Harvesting: Possible products include sulfate, sulfur, and potentially biomass or specific biochemicals created by the bacteria while fixing 𝐶𝑂2

. 

Comparison of Product Price: MISO-based vs. Contemporary Biotech 

Note: MISO is a newly discovered process (2025) and specific, large-scale industrial economic comparisons are not yet available in literature. The following is based on general industrial biotech trends. 

Feature	Contemporary Biotech	MISO-Based Biotech (Projected)
Feedstock Cost	High (e.g., glucose, specialized media)	Very Low (e.g., Waste sulfide, rust/iron oxide)
Energy Input	High (Aeration, agitation, heating)	Low (Often anaerobic, ambient temp)
Operational Costs	Moderate to High (Sterilization, complex media)	Lower (Simple, potentially continuous)
Capital Investment	High (Stainless steel tanks)	Moderate (Similar to, or slightly lower than, conventional reactors)
Waste Management	Costs for disposal	Potential for valorization

Price Analysis: 

• MISO Potential: MISO processes can significantly lower costs by using waste materials and reducing energy requirements. The ability to use Fe(III) oxides (rust) as a cheap electron acceptor could make this method more competitive for specialized chemical or waste-to-product manufacturing.
• Contemporary Biotech Cost Structure: Current processes, particularly those involving monoclonal antibodies or complex pharmaceuticals, are expensive, with costs heavily influenced by sterile conditions and high-cost media.
• Conclusion: MISO-based technology is expected to be more cost-effective for treating wastewater and producing bulk compounds, potentially offering a cheaper, sustainable alternative to conventional, energy-intensive fermentation. 

 

2. Microbe discovery holds promise for sustainable biotechnology. Nature 646, 288 (2025) By Jie Li, Shuwen Liu, Hao Song & Shiming Ding