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Bioelectrogenesis is the generation of electricity by living organisms, a phenomenon that belongs to the science of electrophysiology. In biological cells, electrochemically active transmembrane ion channel and transporter proteins, such as the sodium-potassium pump, make electricity generation possible by maintaining a voltage imbalance from an electrical potential difference between the intracellular and extracellular space. The sodium-potassium pump simultaneously releases three sodium ions away from, and influxes two potassium ions towards, the intracellular space. This generates an electrical potential gradient from the uneven charge separation created. The process consumes metabolic energy in the form of ATP.

Taxonomic distribution

Bioelectrogenesis in the form of creating voltages across membranes is universal in living cells, as this is central to the way that cells provide themselves with usable energy, chemiosmosis, and has been since at least the time of the last universal common ancestor (LUCA). The capability is accordingly found in archaeans, bacteria, and eukaryotes including animals, plants, and fungi.

In fish

All fish, like other vertebrates, make use of electrical activity in their nerves and muscles. Some groups of fish have adapted this feature to provide additional capabilities, namely electroreception and the ability to stun prey. Electric fish include some Torpedinidae (electric rays) and Rajiformes (skates) of the class Chondrichthyes, and some Teleosts, in the Mormyriformes (elephant nose fish), Gymnotiformes (knifefish), Siluriformes (catfish), and the Uranoscopidae (stargazers). These fish produce electric currents through their electric organs, which are composed of electrocytes, modified muscle tissue which allows large concentrations of Na+ ions to pass through the cell membrane. The cumulative effect of this process is an electric discharge. These fish are also usually electroreceptive, like a much larger number of species which are weakly electric, mainly for electrolocation of prey. Electrogenesis may be utilized for electrolocation, self-defense, electrocommunication and sometimes the stunning of prey.</ref>

In microbes

The first examples of bioelectrogenic microbial life were identified in brewer's yeast (Saccharomyces cerevisiae) by M. C. Potter in 1911, using an early iteration of a microbial fuel cell (MFC). It was founded that chemical action in the breakdown of carbon such as fermentation and carbon decomposition in yeast is linked to the production of electricity.

Decomposition of organic or inorganic carbon by bacteria is paired with the release of electrons extracellularly towards electrodes, which generate electric currents. The microbe's released electrons are transferred by biocatalytic enzymes or redox-active compounds from the cell to the anode in the presence of a viable carbon source. This creates an electrical current as electrons move from anode to a physically separated cathode.

There are several mechanisms for extracellular electron transport. Some bacteria use nanowires in biofilm to transfer electrons towards the anode. The nanowires are made of pili that act as a conduit for the electrons to pass towards the anode.

Electron shuttles in the form of redox-active compounds like flavin, which is a cofactor, are also able to transport electrons. These cofactors are secreted by the microbe and reduced by redox participating enzymes such as Cytochrome C embedded on the microbe's cell surface. The reduced cofactors then transfer electrons to the anode and are oxidized.

In some cases, electron transfer is mediated by the cellular membrane embedded redox participating enzyme itself. Cytochrome C on the microbe's cell surface directly interacts with the anode to transfer electrons.

Electron hopping from one bacteria to another in biofilm towards an anode through their outer membrane cytochromes is also another electron transport mechanism.

These bacteria that transfer electrons in the microbe's exterior environment are called exoelectrogens.

Electrogenic bacteria are present in all ecosystems and environments. This includes environments under extreme conditions such as hydrothermal vents and highly acidic ecosystems, as well as common natural environments such as soil and lakes. These electrogenic microbes are observed through the identification of microbes that reside in electrochemically active biofilms formed on MFC electrodes such as Pseudomonas aeruginosa.

See also

• Bioelectromagnetism
• Electrocommunication
• Magnetoreception

References

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• Electrophysiology