Bacteria are electrifying

Bacteria can also be a source of electricity - the energy produced from the bacterial metabolism can be directly transformed into an electric current, which can be used in products that need electricity in remote places that are not connected to the electricity grid

Archaeal bacteria (or archaeons) produce methane, which can be burned to produce electrical energy. We also know bacteria that emit molecular hydrogen, which can also be burned to produce electrical energy. There are bacteria that produce ethanol, which can also be used to produce energy.

It turns out that it is possible to extract energy from certain bacteria in more direct and efficient methods - the energy produced from the bacterial metabolism can be directly transformed into an electric current, which can be used in products that need electricity in remote places that are not connected to the electricity grid - such as sensors, flashlights and cordless phones.

The ability of bacteria to generate electricity has been known for almost a century; But only in recent years, as a result of the rise in oil prices and the search for alternative energy sources, from the development of understanding and knowledge regarding physiological mechanisms in which electrons are transferred as part of energy conversion processes, and from the development of fuel cell technology, have they begun to try to apply this ability in a practical way.

The bacterial fuel cells are not yet applied commercially, but their research and interest in them is expanding in recent years. There is an intention to use them, among other things, as a method of sewage treatment (when the organic substances in the sewage are used as the energy sources for bacteria) and as sources of electricity in remote and isolated areas.

The history of bacterial fuel cells began as early as 1911, when Michael Potter connected electrodes to a solution containing bacteria and to a sterile solution, and showed

Passage of an electric current between the solutions. An improvement in the bacterial fuel cells was achieved in 1931, when they added substances that carry electrons (potassium ferricyanide, benzoquinone) to the anode. Later it became clear that some bacteria do not need such carriers, this is because they have natural electron carriers in their membrane and sometimes even complex protein structures, which are located outside the bacterial cell and allow the efficient passage of electrons from the donor bacteria to other bacteria or to the electrode. These structures, which are originally pili of the bacteria, are called microbial nanowires.

Under laboratory conditions, when pure cultures of Geobacter sulfurreducens or Shewanella oneidensis bacteria were introduced into the anode, they were able to generate electricity and even follow the steps of the process. But when it comes to bacteria from external sources, for example those that come from the sewer, it turned out that bacteria of different species are integrated into the electricity production process and that they form biological membranes on the anode.

bacteria that produce electricity (electrigens)

The species Geobacter metallireducens was discovered in 1987 in the muddy bottom of the Potomac River in Washington, by the research group of Prof. Derek Lovely from the University of Massachusetts. Later, additional species in the genus Geobacter were found in additional terrestrial and aquatic sources. Currently, 13 species are defined in the genus.

Geobacter are anaerobic switches, using metal ions (instead of oxygen) as final electron acceptors in the respiration process. They can be used to purify water from metals and organic impurities.

Geobacter bacteria have special gates made of proteins, which allow the bacteria to donate electrons, both to other bacteria and to the electrode. The diameter of the capillaries is about 5-3 nanometers and their length is about 20 micrometers (10 times the length of the bacterium) - and they are covered by the protein that is the last electron carrier in the chain - which donates the electrons to the final electron acceptor. After being separated from large amounts of bacteria, it will be possible to use these capillaries for the electronic industry as tiny conductors (nanowires).

Bacteria in the genus Shewanella are also aerobic al-switches, which use metal ions as terminal electron acceptors, and use them to clean water from strontium and chromium impurities. But unlike the capillaries of Geobacter, several capillaries of Shewanella coil together and form conductors that are about 50 nanometers in diameter. Currently, 49 species are defined in the genus.

The technology of bacterial fuel cells is still in its infancy, but the combination of environmental cleaning and electricity generation by bacteria looks promising.

Dr. Dror Bar-Nir teaches microbiology and cell biology at the Open University. The article was published in "Galileo" magazine.