22: Extremophiles- creatures living on the edge

Earth only has a limited amount of space, and so not many creatures can live in the exact same parts of it. Creatures like foxes and badgers have managed to get themselves a pretty good deal, living mostly in areas that are not too hot or too cold, and where there is food and fresh air. However, as these areas are already taken, other creatures have been pushed to the margins a little and have been forced to survive in slightly less-nice environments, e.g. reindeer in the Arctic and Fennec foxes in the desert.

Some other creature have really really been forced to the edge, living in conditions that might seem almost impossible to survive in. These hardy creatures are called extremophiles (extremo=extreme, phile=lover), and they are the topic of this week’s plog. We’ll be looking at what they are, how they survive and how they have to potential to teach us about life in space!

The Milky Way Galaxy- extremophiles can teach us about life in space.


Air, or more specifically oxygen, is pretty important for survival, as you will know if you’ve ever tried to hold your breath for more than 30 seconds. The reason why it is so important is that oxygen plays a critical role in creating energy in the body. Without this energy things like legs and hearts and brains don’t survive very long. However, some creature have managed to adapt to life without oxygen, and these are called anaerobes. Most anaerobes are bacteria or small creatures called protozoa which are made up of only one cell. They live in places like deep sea hydrothermal vents (cracks in the sea floor where heat and gas from inside the earth’s crust is released) or at the bottom of really stagnant lakes where there isn’t any oxygen.

Instead of making energy with oxygen, anaerobes either use fermentation, or in the case of the creatures living on hydrothermal vents they have adapted to use other substances like the sulphur spewing out of the vent to make energy. There are only three species, all belonging to the group Loricifera, which are multicellular and can survive without oxygen. These Loricifera are smaller than 1 mm, live more than 3,000 meters below the surface of the very salty L’Atalante Basin lake in the Mediterranean, and spend their whole lives in the dark without oxygen. Doesn’t sound great but they seem to enjoy it.


Sticking with the deep sea hydrothermal vents, which are releasing sometimes literally boiling hot water, our next extreme creatures are hyperthermophiles which like it hot! They can survive in anything above 60 °C (140 °F) though are happiest above 80 °C (176 °F). Normally life struggles at high temperatures because proteins in the body start to lose their shape with the heat, meaning essential internal reactions can’t happen. Hyperthermophiles have adapted to change their protein structure by building extra little bridges in the proteins to make sure they hold together even in high heats.

The most heat tolerant hyperthermophile known is Strain 121, which can happily live in temperatures up to 121 °C, hence the name. They live at hydrothermal vents, but hyperthermophiles can also be found in places such as hot springs.

A deep sea hydrothermal vent, spewing out hot water and gases. It is so deep there is no natural light here (Picture: NERC/NSF Chesso consortium )


Of course this wouldn’t be an Arctic plog without exploring cold regions too. However, the creatures in cold places are often a lot bigger than other extremophiles. Creatures like musk oxen, polar bears and penguins live in some of the earth’s coldest conditions at the poles, often averaging -40°C (-40oF). Being big is an advantage in cold places, as it means you can have thick fur and fat layers for insulation, as well as having a smaller area to volume ratio meaning that there’s a smaller amount of body surface to lose heat from compared to your overall size. There are some behavioural adaptations too, to help with survival, like penguins huddling together to share body heat and polar bears hibernating through the harshest coldest parts of winter.

Not all cold weather extremophiles (called cryophiles) are big though. The Antarctic midge is 2-6 mm small, and survives by burrowing into the snow. It can’t actually survive in temperatures below -15oC (5oF, rookie…), but it is actually warmer in the snow than the surrounding air so they can survive there quite happily.

A musk ox, which survives the cold because its large body size, thick insulating fur and cosy fat layers (Picture: U.S. Fish and Wildlife Service/Public Domain)


The inhospitable environment created by salt has been used for centuries to preserve foods like meat, making sure that the things that the moulds and bacteria that usually would make it go off can’t survive there. We need some salt in life, but at high levels and especially in water it can become deadly over time.

Nature likes balance, so for example if you pour some fresh water into some salt water, the fresh water won’t just clump together but will spread out as evenly as possible to dilute the salty water in a process known as osmosis or diffusion. This happens, though much slower, in bodies. We have a lot of fresh water in our bodies, so if we go into salty water, the fresh water in our cells starts to very slowly leave us, as it tries to evenly dilute the salty water around us. This is okay for a few hours swimming in the sea, but over long periods of time for small organisms it can cause so much moisture to seep out of their cells that they dry out and can’t survive. Also this is why you shouldn’t drink sea water because lots of that actually can kill you…

Halophiles, which can survive in the salt, deal with this by filling their cells with compounds that attract water, replenishing their losses. Halophiles include things like yeasts, certain fungi and bacteria, and they can be found in places like the Dead Sea and the Great Salt Lake (Utah), surviving levels of saltiness 9 times greater than that found in the sea. Halophiles can be used in the fermentation of salty things like soy sauce, salted cod and saukraut.

It’s not just bacteria, a group of sheep in the Orkney Islands called North Ronaldsay Sheep have little access to fresh water for drinking, and seaweed is an important food source for them, so they have adapted to withstand salt levels that would kill other sheep breeds.

File:North Ronaldsay sheep near Westness - geograph.org.uk - 176595.jpg
North Ronaldsay Sheep in Orkney quite happily eat seaweed (Picture: Lis Burke / North Ronaldsay sheep near Westness / CC BY-SA 2.0)


There are many other extreme situations creatures can survive in, including extremely acidic, alkali, radioactive, high pressure, dry and high sugar. However, a lot of them are single-celled bacteria type things and this article would start to get a bit repetitive, so instead I thought we could have a quick look at one creature which is an extremophile in many ways. This is the tardigrade (also known as a water bears or moss piglets but these imply that it’s a lot cuter than it actually is…). It is a class of creature which are all 1 mm or smaller in size, who lay eggs and have 8 little legs with claws on the end. What makes them special is their ability to survive very cold and dry periods for a long time. If their environment isn’t very hospitable, they curl up into a lifeless ball called a tun, and basically go into a very deep sleep. They can survive in this state for decades, simply waiting for warmer, wetter conditions to return. Experiments have seen them survive temperatures as low as −272 °C (−458 °F) and as high as 149 °C (300 °F), happily waking up again afterwards. They can also survive in space, which leads us nicely on to why extremophiles can help us understand more about aliens…

File:Adult tardigrade.jpg
A microscopic tardigrade. Told you they weren’t cute… but they’re still pretty cool! (Picture: Goldstein Lab/ Wikimedia Commons/ CC BY-SA 2.0)


When we speak about ‘extreme’ environments, we’re actually just talking about environments that would be difficult for us humans to survive in. Life is adaptable, so to a hyperthermophile, sitting in boiling water isn’t extreme but just normal. When we look out to planets in space, they are very different from earth in terms of their temperature, pressure, the kinds of gases that they have in their atmosphere, and the amount of radiation they receive.

‘Alien’ just means a thing from another place, so e.g. a plant that isn’t native to an area or a person from another country (though maybe don’t run around calling your foreign pals aliens). From earth’s perspective an alien is anything not from earth, so if we want to understand what aliens are like, if they exist, we can use extremophiles to understand how life can survive in environments very different to our own. Looking at the general trend in extremophiles here, it seems like that if there is life out there it’s some kind of bacteria rather than a green guy with a bulging forehead, so sorry if that ruins the image a little.

Small or multicellular and complex, extremophiles show us just how adaptable and flexible life is when it is looking for a way to survive. Not bad for what are often microscopic blobs!

For more info:

Basic info on extremophiles: https://www.bbc.co.uk/bitesize/guides/z9pd6yc/revision/10

A quick National Geographic video on extremophiles: https://www.youtube.com/watch?v=MY1d5Saqrc4

Music: kongano.com

Cover photo: Steve Jurvetson/CC BY 2.0

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