Top 10 most unusual life forms

So a big puzzle in astrobiology is where exactly we might find life and what form it may take. Most scientists regard life as having a few prerequisites to exist in the first place; notably water, oxygen, carbon, a temperature between 0-50°C… It’s a fair assumption to make, given that we only really have the Earth as an example.

But with a sample size of one, we’re really in no place to be drawing up hard and fast rules. We really don’t know what conditions life could thrive in. We don’t even know for certain what life might be made of.

So here are my top 10 most unusual life forms. Extremophiles, or living things that are just plain unusual. Obviously, all of these things exist on Earth. If life like this can exist on Earth, it can exist elsewhere. If similar things can exist, then by probability alone, it’s no leap of faith to say that they probably will exist somewhere. The only question we need to ask is where.

1. Deinococcus Radiodurans

D. Radiodurans holds a place in the Guinness Book of Records as the “World’s toughest bacterium”. It can grow up to 3.5µm big, and likes to stick together in little groups of 4 (called tetrads). Radiodurans can survive a dose of 5000 Grays of radiation (10 Grays can kill a human being). Some of these guys can survive brief exposure to up to 15000 Grays. Now that’s impressive.

On top of that, it can survive extreme cold, dehydration, exposure to vacuum and acidic environments. That makes it a polyextremophile with such resilience that some have even conjectured that it could’ve come from space!

If any catastrophic event were to destroy most of planet Earth, these hardy little microbes would probably survive. Some scientists have even considered using the DNA in Radiodurans as a way of storing information that would survive a nuclear catastrophe.

2. Snottite

These delightfully named bacterial colonies really do look exactly as you’d expect. To look at, they appear to be stalactites made of mucus. Lovely.

They’re actually acidophile bacteria which live off volcanic sulfur compounds in the warm, wet mexican caves where they live. I’m just guessing here, but chances are fair that they actually metabolise that sulfur into sulfuric acid (chemosynthesis). As a result, they live in the kind of acidic conditions that would kill most other life forms. Bizarrely, they aren’t isolated to those mexican caves either. They’ve also been found in drained mines in Wales, of all places.

3. Strain 121

I’ll admit, this microbe sounds like something from a sci-fi novel…

Strain 121 is a hyperthermophile. It lives in places with excessive temperatures. In fact, it’s able to survive and reproduce at up to 121°C. They can survive temperatures of up to 130°C, resuming life as usual when the temperature drops back down again.

Nothing else (that we know of) can survive these temperatures. Before Strain 121 was discovered, it was believed that 15 minutes in an autoclave oven at 121°C (standard procedure for sterilising medical equipment) would kill all living organisms.

4. Desulfotomaculum

These are the first organisms ever discovered that live completely independently of the Sun!

Discovered almost 4km deep, down a South African gold mine, they glean all of their energy from radioactive metals (like uranium) in the rocks. They use this energy to reduce sulfate molecules into hydrogen sulfide. Effectively, “radiosynthesis” instead of “photosynthesis”!

Researchers found that it’s quite likely these bacteria have been living independently of Earth’s surface for 20 million years. It really makes you wonder what other niches on this planet have been colonised by life — without us even realising it yet.

5. Colwellia psychrerythraea

Thriving in the sub-freezing waters of the Arctic Ocean, Colwellia is a psychrophile. It thrives in freezing cold conditions. It can survive completely encased in tiny bubbles of saline water trapped within the ice. Temperatures of -20°C are fairly normal for these things.

Amazingly though, some studies have shown that these microbes can survive temperatures as low as liquid nitrogen (-163°C). Not just survive, but continue to metabolise! Things run very very slowly at these temperatures, of course, but seemingly they do keep going.

Life that can survive those sorts of temperatures gives a lot of hope that something might be living out there on Titan or Europa…

6. Mimivirus

Mimivirus (full name, Acanthamoeba polyphaga mimivirus), unlike the other microbes mentioned so far, isn’t a hardy survivor. Actually it lives in conditions not unlike those you or I would enjoy.

What’s amazing about mimivirus is that while, as it’s name would imply, it’s a virus, it’s actually bigger and more complex than some types of bacteria. While it still acts very much like a virus, in that it’s an obligate parasite, it has a large genome (around 1.2 million base pairs) and it posesses genes not normally found in viruses (such as genes for lipid and amino acid metabolism). It even contains genes that some bacteria lack. In fact, when it was first discovered, it was mistaken for a new form of bacteria!

Some have started wondering if mimivirus is our first hint at an entirely different form of life — non-cellular life. It could represent an entirely distinct domain of life (alongside bacteria, archaea and eukarya), possibly having evolved before cellular life took hold.

A few theories (such as Serial Endosymbiotic Theory and Viral Eukaryogenesis) postulate what role viruses may have played in the evolution of complex life itself. Regardless of one’s opinions on such theories, the fact remains that such “acellular” life may exist in more complex forms off this planet.

So far, I’ve been concentrating on microscopic organisms. It would be easy to assume that more complex forms of life prefer more typically “Earth-like” conditions. That assumption, it seems, is far from the truth!

7. Hesiocaeca methanicola

A number of “ice worms” live in glacial ice, hiding from sunlight and doing their best to stay cold as they feed on algae and plankton trapped within the ice. These creatures cannot actually survive high temperatures. They start to die a few degrees above 0°C. Around 5°C, their tissues actually liquify — they melt.

As if that wasn’t enough, hesiocaeca methanicola (the methane ice worm) actually lives on the ocean floor in an ecosystem based around methane clathyrate ice (that’s water ice containing trapped molecules of methane).

For obvious reasons, ice worms haven’t been studied in any great detail…

8. Triops

The triops is an interesting little animal. With a number of species found on every continent except antarctica, these creatures are specially adapted to survive long periods of drought.

Their eggs need to be dried out before they’ll hatch — entering a kind of suspended animation (known as diapause). They can lie dormant for over 50 years, withstanding drying out completely, extremes of temperature and even vacuum. On contact with water (in the wild, during rainy seasons), they hatch out and quickly colonise whatever puddle they might find themselves in — growing to their full size of several centimetres in just a couple of weeks.

This tactic has worked pretty well for the little creatures. They’re a good contender for the oldest living species on Earth, having been seen virtually unchanged in fossil records dating back 220 million years!

Incidentally, you can often buy triops eggs with little aquaria. They’re often sold to kids for school science projects, just like their close relatives the brine shrimp (sea monkeys). Actually, I used to keep some myself – this picture is of a former pet of mine!

9. Hydra

Hydras are a tiny pond-dwelling creature. Again, you find them in freshwater pools across the planet, where they catch other tiny water creatures with their tentacles.

Related to jellyfish, hydras are biologically immortal.
Yes, that’s right. They have the ability to regenerate any lost appendages and they don’t actually age. All their cells divide continually, diluting toxins and defects, meaning that if nothing kills a hydra (such as predators or bad conditions) they simply won’t die. Ever.

10. Tardigrade

Tardigrades are, quite simply, the hardiest multicellular animals in the world. They can survive 1000 times as much radioactivity as most other creatures, live for a decade without water, briefly survive temperatures lower than liquid nitrogen and hotter than boiling water.

A recent experiment actually involved exposing them to open space — hard vacuum, raw unfiltered sunlight, extreme heat and radiation all at the same time. Some of them survived even this. Practically indestructible.

Tardigrades, once again, live practically everywhere on Earth.

It seems, life is pretty tough. If life here on Earth can survive such outlandish conditions, who knows what life elsewhere might have adapted to. Perhaps we shouldn’t be too hasty to write off other planets in the solar system as “too cold” or “too acidic”…

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
This entry was posted in astrobiology, Imported from Livejournal and tagged , . Bookmark the permalink.

24 Responses to Top 10 most unusual life forms

  1. Pingback: Anomalocaris! | Supernova Condensate

  2. Anonymous says:

    This article was extremely interesting, especially since I was searching for thoughts on this subject last Thursday.

  3. Anonymous says:

    ‘radiosynthesis’ might be stretching it since they use the byproduct of radioactive decay (H2) to perform their sulfate reduction metabolism, whereas photoautotrophs use solar radiation directly to perform photosynthesis.
    nice site from what I’ve seen so far, the only thing I might suggest would be to look into/cite the primary literature a bit more. is your friend :)

  4. ryttu3k says:

    Oh, I meant my class personally hasn’t studied proteins XD
    *grin* That’s the general umbrella term I’m going for!

  5. invaderxan says:

    Oh I see… Guess I was being dense. :P

  6. invaderxan says:

    Well, people have studied some proteins a lot. It’s just that there are a lot of different proteins out there…
    Y’know, it sounds like you might find Planetary Science an interesting thing to study. It would have some amount of both Astrogeology and Astrobiology (as well as atmospheric science for good measure)…

  7. dr_psycho says:

    Tardigrades In Space (TARDIS) project.

  8. ryttu3k says:

    Isn’t it? XD I’ve seen it also written as ‘freaky radiation-proof berry’, but that’s not quite as technically correct XD
    Yeah, I know ^_^ Man, Enceladus is interesting… it’s tiny, it’s far from the sun, so what’s keeping those tiger stripes warm? I want to know! *hops impatiently*
    Ooh, right – we haven’t really studied proteins much :( I’d like to! We just haven’t done anything of it.
    Give us time XD (Well, I’m kinda wavering between astrobiology proper and… astrogeology, I guess? Mars rocks! :D)

  9. invaderxan says:

    Extremely useful… A classic example too, of life making use of that which is available to it! :)

  10. helen99 says:

    I liked the Desulfotomaculum’s ability to synthesize radiation rather than sunlight. What a very useful talent!

  11. invaderxan says:

    Marvellous berry that withstands radiation! That’s brilliant…
    As Desulfotomaculum goes, some theories go that smaller planets and other objects (Enceladus, for instance) might be kept warm by radioactive decay. It’s especially interesting that life can exist without needing the Sun!
    Methanicola, I think, is made out of proteins like anything else. Those proteins denature just above freezing. Technically, it’s disintegrating and not melting — though the end result is pretty much the same.
    Astrobiology certainly is cool. It’ll be even cooler when we actually do find life out there, though…

  12. invaderxan says:

    Yeah, their original name was german — kleiner Wasserbär. It means little water bear. :)

  13. invaderxan says:

    TARDIS project? You mean the Southampton Uni e-prints project? Or am I being dense here?
    Thanks for the references dude — and no, I hadn’t read that MNRAS paper. Hmmm…

  14. invaderxan says:

    If it makes you feel any better, I thought something similar, reading about Mimivirus…
    “400-800nm? Hey, that’s more or less the wavelengths of visible light!”

  15. invaderxan says:

    Yeah… Someone should make tardigrade plushies. I’d buy one!

  16. dr_psycho says:

    Love that TARDIS project, how awesome!! Almost on a par with the eagerly anticipated Cramer experiment into Retrocausality.
    As an addition can I throw the following beauties into the mix:
    – Bacillus anthracis (Spores – hard as a stale granite sandwich)
    ……….. Infact spore forming bacteria in general, just wanted to get Anthrax in there. You have probably read
    “Survival of bacteria and spores under extreme shock pressures”, (Monthly Notices of the Royal Astronomical Society, 2004, vol. 352,4,1273-1278) – Throwing evidence in the Panspermia direction.
    – Turritopsis nutricula (immortality)
    – Shewanella oneidensi (Dust living bacteria- See E.Coli)
    – E.Coli…. Yes that’s right, plain old ‘bog’ standard gut bacteria that can also survive up to 1680 megapascals!
    Microbial Activity at Gigapascal Pressures ,Science 22 2002:
    Vol. 295;5559:1514 – 1516

  17. davidnm says:

    It kind of shows how conditioned by specialist research I’m getting that my immediate reaction the size of Deinococcus Radiodurans was to think, ‘Oooh, it’s bigger then the K-band!’
    I need to get out more…

  18. underwr1tten says:

    I visited Harvard’s natural history museum about a year ago, and in the arthropod room, they had a picture of tardigrades a lot like the one above. I think they called it a microscopic teddy bear or something…I was rather distracted by their beautiful hymenoptera collections XD

  19. Tardigrades actually look surprisingly cute, almost like cuddly little stuffed animal monsters!

  20. ryttu3k says:

    Holy shit, I LOVE extremophiles! Although you didn’t mention my two favourite Deinococcus Radiodurans tidbits – its name literally translates as ‘marvellous berry that withstands radiation’, and its nickname is CONAN THE BACTERIUM. HEE XD
    Snottites are brilliant XD Caves + extremophiles + sulphuric acid! AWESOME.
    Desulfotomaculum is COOL. Hmm… it’s fairly common to have large bits of space rock flying around. They don’t exactly have solar sources, but some of them MUST contain radioactive material. Hmmm…
    Hesiocaeca methanicola sounds WAY cool. What’s their tissue made of? It must have a large proportion of water if it MELTS at just above freezing!
    And, of course, tardigrades are the BEST. EXTREMOPHILES. EVER. And so cute!
    Man, THIS is why I want to be an astrobiologist. It’s just about the coolest area of study ever!

  21. invaderxan says:

    Totally… it’s amazing how many ecosystems depend on tiny things like plankton!

  22. invaderxan says:

    Cool. :)
    I’m really glad you liked it!
    FYI, Triops hatch best in distilled water… There’s a website with a load of good advice on keeping them!

  23. Studying phytoplankton has given me a new appreciation for the interesting nature of some of the creatures that are here on earth. :)

  24. I really enjoyed reading this post, and have actually shared it with a few people who I thought could appreciate it. ^_^
    I actually have some Triops eggs, but I’ve had yet to hatch them.

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