Living Life On The Edge- Extremophiles

Humans, like most organisms on earth, are adjusted to certain conditions. We like our environment to be mild, kind of like Goldilocks – not too hot but not too cold. Sure, we can survive a bit of hot weather or some snow but we will need additional support like an air-conditioner or a coat. But imagine living in boiling water that is so acidic that it can eat through metal. Doesn’t sound very cozy does it? In fact, you might find it hard to believe that any organism can even survive that kind of extreme environment, let alone thrive in it. Yet mother nature astounds us all by the existence to extremophiles – organisms that live in “extreme” environments.

Now when I say extreme, I mean really extreme. They can be found in boiling conditions of near 100°C (thermophiles), highly acidic conditions of pH 2 or less (acidophiles), living under extreme pressure (piezophiles), living in conditions with a low availability of water (xerophiles) etc. These creatures are so well adapted to harsh environments that most of them won’t survive in what we consider to be normal conditions. For example, if you were to take a Pompeii worm (Alvinella pompejan) from its home – hydrothermal vents in the Pacific Ocean where temperatures are around 60 °C and pressure can reach up to 250 atmospheres – and place it in a freshwater lake, it will die immediately.

Pompeii worm – gets its name from the Roman city of Pompeii that was destroyed during an eruption of Mount Vesuvius in AD 79

So what makes these organisms so special and why are we interested in them? Well because they are so different from what we normally see, scientists have done a lot of research on them and realised that they can be very useful to us. For instance, Thermus aquaticus – a thermophile – has proved to be vital in the field of biology. They produce an enzyme called TAQ polymerase which can withstand high temperatures like 95 °C without getting denatured. This enzyme is used in PCR (Polymerase chain reaction) to synthesise new strands of DNA at around 72 °C. PCR allows scientists to replicate a piece of DNA billions of times over a span of a few hours, and without this process, nearly all work requiring DNA replication, from forensic science to genetic testing, wouldn’t be possible.

T. aquaticus – an important source of thermostable enzymes

Another field where extremophiles are a subject of interest is space. NASA is in fact studying an extremophile – Deinococcus radiodurans. They can survive cold, dehydration, vacuum, radiation and acid, and therefore, is considered to be a polyextremophile. These characteristics have allowed this bacterium to earn a place in The Guinness Book Of World Records as the world’s toughest known bacterium. The characteristic that NASA is specifically interested in is its extreme resistance to radiation. They can withstand doses of radiation 1500 times greater than what would kill a human. They do this by having multiple copies of its genome and has rapid DNA repair mechanisms. Understanding how D. radiodurans does this could allow scientists to bring dead cells back to life. For NASA, harnessing this DNA repair mechanism could offer clues for building better spacesuits and spacecrafts.

D. radiodurans – nicknamed Conan the Bacterium (like Conan the Barbarian), due to its sturdiness

While D. radiodurans is the most resilient bacterium, we have tardigrades, which are considered to be the most resilient animal in the world. These polyextremophiles, colloquially known as water bears, have been discovered 5546m up a mountain in the Himalayas, in Japanese hot springs, at the bottom of the ocean and in Antarctica. They can withstand huge amounts of radiation, being heated to 150 °C, and being frozen almost to absolute zero. They even managed to survive and breed in space! In 2007, thousands of tardigrades were attached to a satellite and sent into space. After the satellite had returned to Earth, scientists examined them and found that many of them still lived. Some of the females had laid eggs in space, and the newly-hatched ones were healthy. Hence, these micro-animals are an ideal subject for further research and we can possibly learn a thing or two from it about surviving in space.

Tardigrade – the name means “slow stepper” due to its very slow movement.

Space is known for its harsh conditions and all the planets that we know of are not exactly habitable. So if life exists outside of earth, they will most likely be adapted to extreme conditions – like our extremophiles. Astrobiologists rely heavily on extremophiles not only for investigating life on other planets, but also for trying to find answers about the origin of life. Clearly these organisms have been around since time immemorial and will continue to do so for a long time. Therefore, it is important that we continue to research them so that we get some insights on how to survive the harsh conditions that the future might have in store for us.

- written by Kartika Girish Nair