Have you ever seen the tentacles of microorganisms that can conduct electricity? Do you want one?

Produced by: Science Popularization China

Author: Liu Qian, Ma Luyan (Institute of Microbiology, Chinese Academy of Sciences)

Producer: China Science Expo

We modern people cannot live without electricity at all times, such as the lights we use to illuminate the night, the computers we use at work, etc. Electricity also exists in nature, such as the strong discharge phenomenon in the sky - lightning, etc. What else can conduct electricity?

microorganism!

As early as 1910, British botanists discovered that the culture fluid of certain microorganisms could generate electricity and created the world's first microbial battery. Currently, scientists have discovered hundreds of microorganisms related to electricity and named them electrochemically active microorganisms.

In addition, scientists have discovered that some electrochemically active microorganisms have a magical "conductive tentacle" that can help these microorganisms transfer electrons over long distances. This "conductive tentacle" is the conductive nanowire of the microorganism.

You generate electricity with love, they conduct electricity with wires

In 2005, scientists first discovered this "conductive tentacle" that can transfer electrons from inside the cell to outside the cell in a microorganism called Geobacillus sulfurreducens, and named it conductive nanowires.

**Conductive nanowires are a type of linear structure synthesized by microorganisms with a diameter of nanometers. **With the continuous deepening of research, scientists have also found conductive nanowires in many microorganisms such as thermophilic fermentation bacteria, cyanobacteria, Rhodopseudomonas palustris, sulfate-reducing bacteria, and Acidithiobacillus ferrooxidans, which shows that conductive nanowires are widely present.

Microorganisms' 'conductive tentacles'

(Photo credit: Sibel Ebru Yalcin/eurekalert, translation: author)

Interestingly, scientists have found that the types and quantities of conductive nanowires in different types of microorganisms are different. For example, the conductive nanowires in Shewanella Oneida are composed of extensions of the cell outer membrane and the periplasmic space.

There are three types of conductive nanowires in Geobacter sulfurreducens, all of which are composed of proteins. Moreover, the conductivity of these three conductive nanowires is not the same. The conductivity of one conductive nanowire is 1,000 times stronger than that of another conductive nanowire.

Conductivity is not white

What role do conductive nanowires play in the life activities of microorganisms? Scientists have found through research that conductive nanowires have two main roles: participating in the physiological metabolism of microorganisms and mediating the symbiotic relationship between microorganisms.

Microbial nanowires

(Image credit: Sibel Ebru Yalcin/eurekalert)

Participate in the physiological metabolism of microorganisms: For example, the conductive nanowires of Geobacter sulfurreducens can transfer electrons in the cell to insoluble iron-containing minerals far away from it, reduce trivalent iron, thereby completing the respiration process and storing the energy needed for life activities. This process is also called iron respiration.

Mediating symbiotic relationships between microorganisms: Conductive nanowires can help microorganisms transfer electrons to other adjacent microorganisms. For example, Geobacter metalloreducing can transfer electrons produced by its own oxidation of ethanol to Geobacter sulfurreducing through conductive nanowires, and Geobacter sulfurreducing uses the obtained electrons to reduce fumaric acid, thereby achieving symbiosis of the two microorganisms in an environment rich in ethanol and fumaric acid.

Scientists have discovered that metal-reducing Geobacter can also transfer electrons produced by oxidizing ethanol to methanogens through conductive nanowires, while methanogens use the obtained electrons to reduce carbon dioxide to methane, thus achieving symbiosis between the two microorganisms.

The conductive tentacles of microorganisms come in handy

With the continuous research on conductive nanowires, scientists have discovered that it has high conductivity and stability, so it has great application potential in the fields of bio-new energy, biomaterials and environmental remediation.

Nanowire-producing bacteria

(Image credit: Sibel Ebru Yalcin/eurekalert)

1. New bioenergy

This is one of the most promising applications of conductive nanowires. Scientists have found that conductive nanowires can be used to develop microbial fuel cells and biobatteries.

Microbial fuel cells are devices that use microorganisms to directly convert chemical energy in organic matter into electrical energy. Scientists have designed a variety of devices that can generate electrical energy simply by cultivating electrochemically active microorganisms. At the same time, scientists have also found that by promoting the expression of conductive nanowires in certain microorganisms through genetic engineering, the power output of microbial fuel cells can be further increased.

In addition, some scientists have tried to collect and purify the conductive nanowires produced by microorganisms and prepare micro-biobatteries based on conductive nanowires. The current density of such batteries is even higher than that of solid metal batteries. This discovery further proves that conductive nanowires have great development potential in the field of new bioenergy.

2. Biomaterials

The conductive nanowires of Geobacillus sulfurreducens still have good electron transfer ability in solution and high-temperature environment, and have certain mechanical strength, making them suitable for constructing new green and pollution-free bioelectronic devices, such as batteries or circuit components in pacemakers. Scientists have also tried to make a composite material with the conductive nanowires of Geobacillus sulfurreducens and polyvinyl alcohol, and found that the composite material has higher thermal stability and a larger conductivity range.

3. Environmental remediation

Microbial conductive nanowires can transform and migrate toxic metals in the environment and have important application value in the remediation of heavy metal-contaminated soil. For example, the conductive nanowires of Geobacter sulfurreducens can reduce toxic soluble hexavalent uranium U (VI) to insoluble tetravalent uranium U (IV), and the reduced tetravalent uranium will adhere to the surface of the conductive nanowires, thereby achieving uranium enrichment and fixation; the conductive nanowires of Synechocystis (a type of cyanobacteria) can help deposit heavy metal arsenic, etc.

Conclusion

In recent years, scientists' increasingly in-depth research on conductive nanowires has not only broadened people's understanding of microorganisms, but also deepened their understanding of the interaction between microorganisms and the environment. At the same time, it has also laid a theoretical foundation for the application of microorganisms in bioremediation, bio-new energy and other fields.

Editor: Sun Chenyu