Discovered a new living creature that feeds electrons

Perhaps such bacteria will survive on Mars

Scientists have installed carbon fiber electrodes (gray) as bait for microbes that absorb electricity (orange). These microbes grow incredibly slowly, so the electrodes are left underground for five months. Photo: Yamini Jangir and Moh El-Naggar

For long centuries, biologists believed that all life on Earth is divided into two types: phototrophs and chemotrophs. The first get electricity from sunlight, and the second - from energy-intensive substances in the environment, like people.

But recently it turned out that on Earth (perhaps on other planets) there is a third kind of life that is able to feed on pure electricity.

The scientists were stunned to realize how widespread such a life could be, which for a long time was hidden from people's eyes. After all, these microorganisms are able to live in huge quantities in mineral-rich veins deep beneath the earth's surface, in oceanic sediments under the seabed, etc.
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Last year, Japanese biologists studied the deep-water iron bacteria Acidithiobacillus ferrooxidans , which oxidize bivalent iron to ferric and live off their energy. Scientists have suggested that these bacteria do not necessarily need iron - and managed to feed them with pure electricity . But the Japanese did not manage to prove that the phenomenon of feeding living creatures with pure electricity exists in nature, although they were able to detect geoelectric current near hydrothermal sources.

American biophysics, too, have been studying the phenomenon of electrotrophs in wildlife for several years. For example, Professor Moh El-Naggar, along with graduate student Yamini Jangir, in search of such an exotic life, climbed to a depth of one and a half kilometers of an abandoned mine in the Black Hills mountain range, which is located in the southwestern part of South Dakota. . They found old rusty pipes left over from the miners - and pumped out some water for the experiment. Scientists have suggested that in this water there may be bacteria that feed on electricity, oxidizing iron in the same way as it was in the Japanese experiment.


Graduate student Yemini Jangir is drawing water from a pipe in an abandoned mine at a depth of one and a half kilometers. Photo: Connie A. Walter and Matt Kapust

Biophysicists placed electrodes in the extracted water sample and passed a current through them, leaving the sample for five months to allow germs to grow.

The results of their scientific work, scientists will publish in the near future. They will join numerous groups of biologists who are trying to find evidence of a natural phenomenon known as direct electron transfer .

In recent years, several discoveries have been made that confirm the theory that bacteria that eat electricity are common on Earth — they are much more numerous than anyone had imagined. Recent samples from the seabed off Catalina Island, near California, have revealed a wide variety of bacteria that produce electricity from metals and minerals.

Now scientists are trying to understand how the metabolism of bacteria that produce electricity directly from the environment. Japanese colleagues have shown that heme-containing proteins in the membrane are involved in electron transfer from the external environment. That is, the current passes directly through the membrane - a process that was previously considered impossible.



In the electricity itself is not surprising. People and all other living organisms eat electricity at the cellular level. As Nobel laureate Albert Sainte-György once said romantically about this fundamental principle of life, "life is just an electron seeking rest . " The question is how we extract it from the environment.

Professor El-Naggar and other groups of scientists are studying a new kind of organism called lithoautotrophs - organisms that use inorganic substances for energy and are able to synthesize all the components of their cells from carbon dioxide and other inorganic compounds. In other words, these bacteria extract energy from iron, sulfur, manganese and other inorganic compounds. Under certain conditions, they can live on clean electricity.

The ability of such bacteria to absorb electrons in a pure form - the so-called direct electron transfer - is a very interesting phenomenon, because it seems to violate the basic laws of biophysics. By law, the thick cell membrane works as an insulator; electrons should not pass through it. “No one wanted to believe that a bacterium could take an electron from inside the cell and move it out,” said geobiologist Kenneth Nealson in a lecture last year to members of the Society for Applied Microbiology in London.

But the detected microbes are capable of that.


Lecture by Kenneth Nilson

In 2006, biologists were the first to understand how this mechanism works with the help of three specialized proteins . They are located in the membrane and form a conductive bridge, through which electrons are transferred from the cell to the outside. However, scientists still continue to discuss specific details, but the fact of the existence of such a mechanism has been proven.

After that, biologists began to look for evidence that there is a reverse transfer of electrons from the external environment into the cell. In 2009, it was proved that the bacterium Methanococcus maripaludis is able to multiply on the electrode, but only last year the mechanism was discovered how it receives electricity - it turned out that for this bacterium uses a special enzyme that pairs an electron from a conductor with a proton from water, to create a hydrogen atom, a common food among bacteria.



Although this kind of "cheating", that is, not direct electron transfer, but some scientists believe that other bacteria still know how to directly remove electrons from the environment, that is, direct electron transfer still exists.

Biologists believe that the study of new types of bacteria is still in its infancy and promises many discoveries. Professor El-Naggar compares modern experiments with the first experiments in neuroscience, when scientists poked frogs with electrodes to make their muscles contract.

Scientific discoveries in this area can shed light on how life began on Earth. Moreover, these discoveries significantly expand the potential habitat of microorganisms on other planets, where life can hide under the surface of the planets.


Surface of mars

Such microbes can survive, for example, in the extreme conditions of Mars, because Mars has a lot of iron and there are underground reservoirs of water. If we have a system for extracting electrons from iron and access to water, then this is the most necessary for the metabolism of such bacteria.

So if during the next missions to Mars live microorganisms are found, it will not surprise biologists at all.