Forum

Extremophiles are organisms that thrive in harsh environments where you would think nothing could live. When looking at extremophiles on Earth and the environments they live in it does make you wonder why organisms haven’t been found on other planets yet.

Extremophiles may have been the first life that existed on Earth. They don’t exist, they thrive in harsh environments and don’t do so well when taken out of the harsh environment that they love so much. Extremophiles are varieties of Archaea and bacteria and are classified according to the environment in which they live.

Just to show you how easy it would be for extremophiles to exist on other planets, moons, satellites, asteroids or comets I will run through a few types below.

Temperature Loving Extremophiles.

The lowest temperature for extremophiles is -18°C. The main problem with life and low temperatures is that the cold forms crystals of ice which can rupture the cells. Psycrophiles are the type of extremophiles that just love low temperatures. I am therefore by definition not a psycrophile.

They grow best at 4°C and do not like temperatures above 12°C for reproduction, very fussy! As mentioned before the main problem is ice freezing their cells and they get round this by making the membrane of the cell more fluid and therefore less likely to crack and rupture. They also use soluble compounds that lower the normal freezing point of water and in the case of glycerol they can survive down to -60°C.

Chlamydomonas Nivalis a Psycrophile

Hyperthermophiles love the heat. They can reproduce at temperatures greater than 80°C living in temperatures of 100°C or even more. There are more than 50 different types of Hyperthermophiles and the most resistant found to date grows on the walls of black smokers on seafloors. These Hyperthermophiles are called pyrolobus fumarii and reproduce at 105°C but below 90°C they don’t grow at all.

The temperature range of extremophiles means that they could exist on comets or asteroids, on some of the planets and on some of the satellites like Europa with its outer icy surface and possibly hot interior with possible hydrothermal vents.

Black Smoker Hydrothermal Vent

Extremophiles That Can Survive Radiation

The Sun can make us brown but it can also destroy DNA. We are lucky because we are protected by the atmosphere but other planets throughout the solar system don’t always have this luxury. Deinococcus radiodurans an extremophile that can survive the harshest of radiation environments. It is one of the toughest extremophiles and can withstand high ultraviolet and gamma radiation. It can do this because it is an excellent rebuilder and rebuilds its DNA from fragments that had been damaged by the radiation. This ability may be due to it being ring like which keeps fragments closer together and allows them to rebuild.

Radiation is a problem throughout the solar system and the other planets aren’t protected as well as ours. But radiation extremophiles gives us hope that life may exist in the most irradiated of environments.

Deinococcus Radiodurans

Acidic and Alkaline Extremophiles

There is a scale called the pH scale and life as we know it must live at the centre of the scale. This type of extremophiles can survive in all sorts of acidic and alkaline environments at either end of the pH scale. Acidophiles, as the name suggests, survive in acidic environments by keeping the acid out and maintaining neutrality inside their cells. This allows them to survive in geochemical environments such as hydrothermal vents and some hot springs.

Alkaphiles live within alkaline environments and survive in the same way as acidophiles by maintaining a neutral environment inside the cells. These can be found in soils with carbonates and soda lakes.

Lake Natron, a soda lake in Tanzania

Salinity Type of Extremophiles

These types of extremophiles require salt to live. We are not talking about the salt found in sea water but twice to nearly 5 times that. They are called Halophiles and can be found in the evaporation basins where the environment may also be alkaline as well.

Halophiles

Extremophiles Subjected to Desiccation

Desiccation is extreme dryness or extreme drying of the extremophile. This isn’t such a good thing because all living things on earth depend on water but the extremophile anhydrobiosis can do without moisture. Anhydrobiosis goes into a state of suspended animation where there is little transfer of water in the cell and no metabolic activity. The organism therefore looks dead when it has dried up but with the application of moisture it comes back to life. This happens in bacteria, yeast, fungi and in plants and animals where water is sporadic.

Tardigrade Extremophile, Dubbed Waterbear, Can Survive in Space Dessicated

Pressure Resisting Extremophiles

Piezophiles can resist under a large amount of pressure. They do this by making their membrane fluid and allowing the cells to pack together. There has been work on Piezophiles on the international space station. They have studied them in a weightless environment and are trying to work out how the weightlessness affects the cells and how they work.

When looking at other celestial bodies for life we were once quite restricted as we were looking for life that could exist within human limitations. Extremophiles give us a larger range of environments that may possibly support life. It may be possible that there is intelligent life existing in the weirdest places in the harshest of environments. This draws us to the conclusion that we should not just look for life in habitats that would suit humans but should continue the search in every nook and cranny in every possible environment.

Read original blog post