We are fascinated by everything that is very different from us, such as organisms that grow in environments where it would be impossible for us to survive naturally. Environments where it was thought, until not long ago, that there could not even be life .
Extremophiles (the suffix “-phylum” comes from the Greek φιλíα , love) have “love” for extreme environments. They are, for the most part, microorganisms from the domains of bacteria and archaea , although there are also algae, fungi and small animals.
Among their powers, they can resist : high radiation ( radiophiles ), high pressure ( barophiles ), high or low pH ( alkaliphiles and acidophiles ), extreme heat ( thermophiles ), extreme cold ( psychrophiles ), extreme drought ( xerophiles ), and high concentrations of salt ( halophiles ).
Conditions that, for us, would be a real hell .
To cope with these “unfriendly” environments, extremophiles developed cellular components (such as enzymes and membranes) adapted to operate where few can.
Now yes, let’s get to know 5 of them more closely.
Tardigrades. offroad survivors
Tardigrades, popularly known as water bears , had to top this list, and occupy a special place in it. Their name alludes to their slow pace, as if they were sloths, but with eight legs instead of four.
These small invertebrates reach half a millimeter as adults, in the case of the largest specimens, and are found almost everywhere. They abound in both terrestrial (in mosses and lichens) and aquatic (freshwater and saltwater) habitats.
More than 1,200 species are known, and they can survive in very diverse environments, resisting more than one extreme condition . That is why they are considered polyextremophiles.
When the going gets tough (extreme cold and dryness, for example), they go into a state called cryptobiosis, in which their vital activity becomes almost undetectable . They reduce their metabolism , their growth ceases and they stop reproducing. They can stay that way for years, until things get better.
As if that were not enough, they resist enormous atmospheric pressures , high temperatures , ionizing radiation and even exposure to outer space , as was demonstrated in 2007. The experiment was carried out inside the Biopan-6 experimental platform of the European Space Agency , during the FOTON-M3 mission.
The vacuum (which imposes extreme dehydration) and cosmic radiation prevent most organisms from surviving in space. Tardigrades , who went on their little spacewalk, are one of the few exceptions.
Haloferax volcanii . To the top of salt!
Haloferax volcanii is an archaea belonging to the Euryarchaea phylum. It was isolated by Benjamin Volcani (hence its name) among the sediments of the Dead Sea , one of the saltiest lakes in the world, in 1970.
Its strong point is, of course, that it withstands salt wonderfully, which is why it is classified within the group of haloarchae.
And it is not only that it resists the great salt concentration, but that it needs it to live. Evolutionarily, it has adapted to saline environments by modifying its intracellular salt concentration . The optimum temperature at which it develops is 45 °C. So the recipe for your ideal home is: hot and very salty water. Kind of like living in a soup.
Pyrococcus furiosus . Hot Hot
This archaea loves heat . So much so that it belongs to the group of hyperthermophiles . Its optimum growth temperature is around 100 °C. It was isolated for the first time in the mud located next to the Porto di Levante beach, on the island of Vulcano (Italy).
Its scientific name, translated, would be something like this: “quick fireball” . Fast because it reproduces very quickly (in 37 minutes) and because it can move agilely thanks to its flagella; ball of fire, for its coconut shape and its love of high temperatures.
Thermococcus gammatolerans . Withstanding radiation
This is another extremophile that resists high temperatures, but its great strength is radioresistance. In addition to developing perfectly at around 90 °C , Thermococcus gammatolerans withstands ionizing radiation like no other (the most dangerous at high doses). It is capable of withstanding 10 times the amount of radiation that would kill a human being.
It was found in 2003 , in the underwater hydrothermal vents of the Guaymas Basin (Gulf of California) , at a depth of about 2,000 meters.
This archaea opens up an interesting field of research on the physiology of radioresistance, which is very useful for finding out how damaged chromosomes are repaired after exposure to radiation.
Helicobacter pylori . Extreme acidity is your home
As not all of them are going to be organisms from remote places, here we have a common neighbor of our guts, whose acidophilic powers bring us some dislike.
This gram-negative bacterium, which owes its name to its helical shape, lives in the extremely acidic environment of the stomach (with a pH around 3.5). To protect itself from hydrochloric acid in the stomach, it secretes an enzyme called urease.
It is estimated that two thirds of the world’s population are infected by the bacteria, although a large percentage show no symptoms.
Bacteria have been with us for thousands of years . It is the cause of inflammation of the gastric mucosa, which can lead to gastritis and ulcers, and predispose to certain types of cancer.
Extremophiles off our planet?
The discipline that is responsible for investigating the possibilities of extraterrestrial life, exobiology, benefits from the study of these microorganisms.
Could our terrestrial extremophiles survive on other planets and their satellites? Possibly. The halopsychrophiles (resistant to cold and salt concentration) that better tolerate high pressures could subsist on Titan, Ceres and Europa , which probably have saline oceans under their surface.
The clouds of Venus, with large variations in temperature, could allow the existence of thermoacidophilic or psychroacidophilic microorganisms (resistant to heat and acidity, and to cold and acidity, respectively).
We still have a lot to know about the possibilities of life outside our planet . But, of course, the extremophiles teach us that what is inhospitable for us, for other forms of life is suitable.
Perhaps the extreme is not so rare. After all, if we consider that the current conditions of the Earth (its average temperature, its oxygenated atmosphere, etc.) represent a short period of time since life has existed, we could conclude that the extremophilic life forms have been the dominant throughout evolution.
References:
Delgado Romero, J.A. (2021) ‘Extremophile Microorganisms. Microbial life beyond its optimal conditions’, University of Seville
Jolivet, E., et al. (2003) ‘Thermococcus gammatolerans sp. nov., a hyperthermophilic archaeon from a deep-sea hydrothermal vent that resists ionizing radiation’, International Journal of Systematic and Evolutionary Microbiology, 53(3), 847-851
Merino, N., et al. (2019) ‘Living at the extremes: extremophiles and the limits of life in a planetary context’, Frontiers in microbiology, 10, 780. DOI: 10.3389/fmicb.2019.00780
Sjomina, O. et al. (2018) ‘Epidemiology of Helicobacter pylori infection’, Helicobacter, 23, e12514. DOI: 10.1111/hel.12514C
Sohl, F. et al. (2010) ‘Subsurface water oceans on icy satellites: Chemical composition and exchange processes’, Space Science Reviews, 153(1), 485-510. DOI: 10.1007/s11214-010-9646-y
