Life at the extreme
From volcanic ocean vents to the tops of the Himalayas, extremophiles have found ways conquer every corner of the planet
How some organisms can survive in the world’s most inhospitable environments
“AN EXTREMOPHILE IS ANY FORM OF LIFE THAT THRIVES OUTSIDE THE NARROW BAND OF CONDITIONS HUMANS CAN TOLERATE”
Although a few organisms with staggering survival skills have been known to us for centuries, the term ‘extremophile’ was first coined in 1974 by a scientist called R D Macelroy. It means ‘extreme-loving’ and refers to any form of life that thrives outside the narrow band of conditions humans can tolerate. Extremophiles have only been studied in detail for the last few decades, but they’ve already challenged many ideas we have about life and its limits. Most extremophiles belong to the domain Archaea. These organisms consist of a single cell without a nucleus, and they’re believed to be the oldest life forms on Earth, dating back billions of years. It’s little surprise that these ancient species are the most tolerant and adaptable, since the young planet would have been a volatile and extreme place enveloped by a toxic atmosphere. Today, extremophiles can be found all over the world in the most inhospitable environments; even the most desolate landscape is likely to be teeming with life invisible to the naked eye.
Thermophiles
In pools and springs hot enough to cause severe burns and even death to humans you’ll find thermophiles feeding on the sulphur and ammonia in the blistering water. These microbes often produce pigments and lend their bright colours to the edge of the water. Heat-loving organisms have fatty acid linings in their cell membranes to stop them disintegrating at high temperatures. At the bottom of the ocean, vents known as black smokers send out plumes of water and minerals reaching 400 degrees Celsius in temperature. The liquid doesn’t boil because of the immense pressure it’s under from the water above, but it still seems like the last place creatures would choose to live. Amazingly, it’s not just microorganisms that can bear to be around these cracks in the
Earth’s surface; busy ecosystems develop and flourish around them, sustained by the nutrients leaking out from the planet’s crust. Bacteria are the first to track down a new vent, followed by hardy bivalves like clams. Larger creatures like tubeworms and lobsters move in later, creating unusual communities that have amazed scientists since they were discovered in the 1970s.
Cryophiles
Frigid water, permafrost, mountain peaks and expanses of ice are havens for cryophiles. These organisms live in parts of the world that remain permanently cold and can withstand temperatures well below freezing, with some unicellular species still active at -25 degrees Celsius. Cryophiles, ranging from bacteria to deepwater fish, often produce antifreeze proteins to prevent ice crystals from forming in their bodily fluids. As well as the freezing temperatures, cryophiles must contend with other stresses like high pressure and low oxygen levels on the seabed and high salinity in sea ice. When times get really tough, some cold-dwellers shut down their bodies and enter a state of dormancy until conditions become more tolerable again.
Acidophiles And Alkaliphiles
While humans are best suited to a neutral ph between 6.5 and 7.5, acidophiles flourish in acidic environments where the ph is 5 or lower. Strong cell membranes keep them safe from the potentially damaging effects of acid, allowing them to live in sulphuric pools, polluted water and even human stomachs. Some aggregate for extra protection, forming slimy colonies called biofilms. Alkaline conditions, at the other end of the scale, can be just as challenging. Alkaliphiles like Spirochaeta americana – bacteria found “BUSY HYDROTHERMAL ECOSYSTEMS ARE SUSTAINED BY THE NUTRIENTS LEAKING OUT FROM THE PLANET’S CRUST”
in salty, mineral-rich mud deposits at Mono Lake in California – cannot survive at a ph lower than 8 and do not need oxygen to respire. By actively driving certain molecules out of their cells in exchange for others, they can produce an internal ph closer to neutral than their surroundings and avoid any damage to their structure.
methanogens
Methanogens are microorganisms that produce methane as a byproduct when their metabolic processes take place in low oxygen levels; living in oxygen-poor swamps and marshes, they’re responsible for the bubbling that can be seen at the surface. Most people know that cows produce levels of methane harmful to the environment, but it’s a lesser-known fact that the blame for this gas really lies with methanogens inhabiting the animals’ guts. Methane-emitting organisms have been found under kilometres of ice and in desert soil. The discovery of methanogens in arid environments is of particular interest to scientists; some believe that methane detected in the atmosphere around Mars could be a sign of microorganisms living on the Red Planet.
polyextremophiles
Few things in nature are simple or fit into neat categories, and there are extremophiles that require an even longer title than the others because they’re adapted to live with multiple stressors. Take Desulforudis audaxviator; this bacteria lives 2.8 kilometres underground in groundwater in a South African gold mine, where it survives on chemicals released by the decay of minerals
in the rock. The groundwater is old and highly alkaline, and temperatures in the mine can reach 60 degrees Celsius. D audaxviator is the only known species that doesn’t share its ecosystem with any other life form, and it’s among just a few organisms that survive in the complete absence of light and oxygen. The name ‘audaxviator’ is a nod to its isolated subterranean life – it’s part of an inscription found by the hero of Jules Verne’s novel Journey to the Center of the Earth and means ‘bold traveller’.
“THE WORLD’S TOUGHEST BACTERIUM MAY HELP US DEVELOP A TREATMENT FOR RADIATION EXPOSURE”
extremophiles And The future
One of the reasons extremophiles are so exciting is that we still know relatively little about them. Every study into the hardy organisms reveals something new about their biology or the potential applications they could have in our lives. One extremophile found in stagnant water in an American cave system showed potential to destroy breast cancer cells. Another, Deinococcus radiodurans, is listed in the Guinness Book of World Records as the world’s toughest bacterium; it’s radiation- and acid-resistant and can survive vacuums and extreme cold. Its resistance to radiation is due to a set of antioxidants that protect its proteins, and researchers hope this knowledge will lead to the development of a recovery pill for people who have been exposed to radiation. On top of this, it produces proteins that emit infrared light. Scientists believe these fluorescent proteins could be used to light up cells and organisms and allow them to watch the processes taking place inside them for longer than is possible with the jellyfish proteins currently used by medical researchers and biologists. Extremophiles were around when the planet was still forming and cooling, and they might hold some of the secrets to protecting it. Since they thrive in the most hostile parts of the planet, they have evolved to use whatever is around them. Organisms like those that rely on iron to digest food have the potential to remove harmful metals and industrial waste products from the environment. One microorganism discovered in Rotorua, New Zealand, in a geothermal field known as ‘Hell’s gate’ prefers acidic conditions and survives solely on a diet of methane. This species could one day be used to reduce gas emissions from landfill sites and thereby help in the fight against global warming. Given the rate at which they’re now being discovered and the variety of abilities they possess, tiny extremophiles could soon be taking a big step into the spotlight.