If, as a result of a global cataclysm, there is no oxygen left in the Earth's atmosphere, then one of the few surviving organisms will be Escherichia coli. Its main trump card is the ability to breathe anything and anywhere: on the surface, in the soil, in the human stomach, and not necessarily with oxygen. Together with E. coli, several hundred species of ancient creatures will remain on the planet, capable of breathing sulfur, iron, uranium and even arsenic.
Poisoned air
In 2010, Felisa Wolf-Simon, a researcher at NASA's Astrobiology Department, while studying the salty California Mono Lake, discovered unusual bacteria. They lived in water, where the concentration of alkalis exceeded 80 times the corresponding indicator in the ocean. Microbes used arsenic for respiration, a poison for most living organisms.
In the laboratory, the find, called the "strain GFAJ-1", was placed in a nutrient solution with a normal content of sugars and vitamins, but completely devoid of phosphates - compounds in which phosphorus comes from the environment. Instead, microorganisms were planted with arsenates (arsenic compounds).
It turned out that in a phosphorus-free environment, bacteria not only breathe arsenic, but also know how to incorporate it into DNA and RNA molecules instead of phosphorus. In terms of chemical properties, these elements are similar - enzymes in the cell may not distinguish phosphate from arsenate, and this happens quite often. True, such a substitution usually ends with the death and petrification of bacteria, but not in the case of the GFAJ-1 strain.
“Anaerobic microorganisms (those that do not need oxygen for life or are deadly. - Ed.) Are able to reduce arsenic, using it in respiration as an electron acceptor. Also, anaerobes are able to breathe sulfates, iron, manganese, uranium, selenium, nitrates. We are talking only about microbes that do not have a formalized nucleus - prokaryotes, including bacteria and archaea. There are fungi growing anaerobically, but this is rare, and among eukaryotes (organisms with a formed nucleus) this is the exception rather than the rule,”says Olga Karnachuk, head of the Department of Plant Physiology and Biotechnology at the Biological Institute of Tomsk State University, to RIA Novosti.
On the left - Felisa Wolf-Simon, who discovered microorganisms that use phosphorus as a building material for cells. On the right - bacteria strain GFAJ-1 in a nutrient solution containing vitamins, sugars and arsenates.
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Ancient and tenacious
More than three billion years ago, the first living organisms on Earth fed on hydrogen and sulfur molecules.
“The most ancient of anaerobic breaths is sulfuric breath. Sulfur, like molecular hydrogen, came from volcanoes. This type of metabolism was used when all life consisted only of bacteria and archaea,”says Olga Karnachuk.
With the appearance of cyanobacteria, whose metabolic product was oxygen, the composition of the earth's atmosphere began to gradually change. About 850-600 million years ago, there was already a lot of O2 in the air. For ancient microorganisms, this meant a disaster - oxygen is as toxic to them as chlorine gas is to humans. Therefore, some died out, others (the so-called obligate anaerobes) fled to anoxic places - for example, underground. There were also those who managed to adapt and learned to neutralize toxic gas.
Over time, some microorganisms "understood": oxygen is a strong electron acceptor and by oxidizing organic molecules with it, you can get a lot of energy necessary for life. This means that the size of the cell increases, therefore, more DNA is placed in it, and the structure becomes more complex - this is how there is a chance to become multicellular.
Animals that can not breathe
“Plants, animals, people - everyone breathes oxygen. This is the most effective way of obtaining energy, therefore, when aerobic respiration appeared, the prospect opened up for living organisms to form higher forms, including humans. Anaerobic microbes are also capable of evolving, but in a different direction. Many of them took the path of combining the two types of breathing. For example, E. coli (Escherichia coli) breathes oxygen, and when it enters the human body (in an anaerobic environment) - nitrates. If the conditions are completely bad, the bacterium is able not to breathe at all, it wanders - this is a completely different type of metabolism. There are practically no such opportunists among the higher forms,”the expert notes.
However, there is one exception - the naked mole rat. This mammal, living in underground burrows, costs for hours a very low level of oxygen, and completely without air will last as long as 18 minutes (for comparison: human brain death occurs on average after five minutes in an oxygen-free environment).
When there is little O2 in the air, the naked mole rat switches to anaerobic breakdown of fructose - due to the fact that GLUT5 channels, which are responsible for the release of fructose into the blood, are synthesized in different tissues. In other mammals, they are produced only in the intestines.
Naked mole rat - the only mammal capable of anaerobic breakdown of fructose.
To help a person
“There are many organisms on Earth that can do without oxygen, because anaerobic conditions are easily created - for example, in a flower pot, compost heap or coastal sediments, even in our own body,” the researcher continues.
While some anaerobes cause serious infection when shot or stabbed, most benefit humans. For example, scientists from the University of California at San Diego taught the bacteria Salmonella enterica to destroy cancer tumors: some salmonella synthesized a toxin that makes holes in the membranes of cancer cells, the second a special protein that activates the immune system, and still others produced a molecule that triggers a self-destruction program in cancer cells.
Methanogenic archaea are used in the production of biogas from ordinary household waste, and sulfate-reducing groups are able to purify wastewater from contamination.
“Today many mines are closed due to the high concentration of sulfate. When coal is mined, a large amount of wastewater is generated, which, after purification, flows into the rivers. If sulfates are not disposed of, fish and other aquatic biota may be killed in winter. We purify mine wastewater from these harmful compounds using microorganisms grown in our laboratory. We create conditions in mines so that sulfate respiration is possible there and all sulfate is removed with the help of bacteria. This technology is already being used in practice in the UK, USA, Germany. We are now just creating biotechnology that can work in the climatic conditions of Russia with low average annual temperatures,”the expert concludes.
Alfiya Enikeeva