Extremophiles

Extremophiles

Extremophiles are organisms that live under conditions injurious to many forms of life. Mankind has used extreme environments for a long time to preserve food. We now know that this is because these techniques kill or suppress the bacteria that would otherwise cause spoilage. A few techniques are to heat (i.e. cook) the food, refrigerate it, salt it, or even irradiate it.

And we all know this works. We have refrigerators and freezers. We have been admonished to cook rare roast beef to an internal temperature of about 140F or as much as 180F for well done beef or all poultry. The reason is to both cook the meat – to convert it from something raw to something yummy – and to kill the bacteria living in the raw meat. 

There are other methods for preserving food that you have encountered in your local grocery store. There are dried vegetables, fruits, and meats, which have been starved of water, inhibiting bacterial growth. Nuts and other foods come vacuum packed to reduce the oxygen available in the package. Processing food by using high pressure can kill microbes. This is used for many products, including guacamole and orange juice.

Meat is cured by salting, as in the familiar bacon and ham. Alcohol is also used to preserve some fruits. This is usually done in conjunction with using sugar as a preservative.

Changing the acidity or alkalinity of the food is another way to lengthen its lifetime. Atmosphere modification is also a useful technique. Food, such as grains, can be put in a container and the air replaced with high-purity nitrogen or carbon dioxide. This removes the oxygen and destroys insects, microbes and other unwanted intruders.

The real point is that mankind has known about various ways to preserve food for millenia. Spoilage of food originates from undesirable creatures (typically microbes of some sort) “eating” the food and releasing wast products. Through some combination of the techniques mentioned above, we have learned to kill the undesirable bacteria that would otherwise ruin our food.

Our experience has led us to some understanding of the range of conditions under which Earth-like life can exist. However research revealed that life is actually hardier than we thought.

Life can be born in the most harsh conditions. Photo by Elena.

Biologists have given the name “extremophile” (meaning “lover of extreme conditions”) to organisms that thrive in environments that would kill familiar forms of life. While the study of extremophiles is still a fairly young science, we can discuss some of the range of conditions under which exotic life has been found.

At the bottom of the oceans, sometimes at extraordinary depths, there are spots where magma has worked its way from the interior of the Earth to the ocean floor. At these points, called hydrothermal vents, superheated water streams away from the magma. This water can be heated to well above the familiar boiling temperature of 212 F, but the huge pressure at the bottom of the ocean causes the water to stay in its liquid form. Water inside these hydrothermal vents can be nearly 700 F, certainly high enough to kill any form of ordinary life.

Only a few feet away from these vents, the temperature of ocean water can be very close to freezing, about 35 F. In this temperature gradient grows an unusual ecosystem.

Heat-resistant, sulfur-breathing life is not the only type that exists in extreme environments On the other end of the spectrum are the cold-loving cryophiles. Life-forms at the cold end of the spectru, have quite different problems compared with their thermophile cousins. If water freezes, it expands and can rupture cell membranes. Chemical adaptations are needed to mitigate the problems of the cold.

As of our current understanding, we know of no eukaryotic life that can exist at temperatures outside the range of 5 to 140 F. While the lower number is below the freezing point of ordinary water, water with high salinity can remain liquid at these temperatures. Microbial life has been observed over a temperature range of -22 to 250 F. An example of a cryophilic organism is Chlamydomonas nivalis, a form of algue that is responsible for the phenomenon of watermelon snow in which snow has the color and even the slight scent of watermelon.

Chemical considerations can give us insights into the ultimate constraints on the temperature of carbon-based life. Due to the bond strength involving carbon atoms, it's hard to imagine life at standard pressure much higher than 620 F; about as hot as the hottest your oven can bake. Of course, pressure can affect the rate at which molecules break apart and the decomposition of molecules can be slower at high pressure. It's probably safe to say that carbon-based life is not possible above about 1000 F at any pressure.

Water is critical to life, however it may be that there are extremophiles that don't need much of it. There are also forms of life that are halophiles (salt loving). In the Dead Sea region of the Middle East, most life couldn't survive. However, there are lichens and cellular life that have adapted their chemistry to maintain their inner environment in such a way as to thrive. Some of these forms of life actually need the high salt environment to live at all.

As with the other food-preserving extremes, life has been found in highly acidic and basic environments and even in the presence of radioactivity a thousand time higher than would kill the hardiest normal forms of life. These observations have certainly broadened scientists' expectations of the range of environments that life can successfully inhabit.

With the discovery of these extremophiles, scientists have intensified their search for the niches that life can occupy on Earth. We have pulled life out of well cores taken from a couple of miles under the surface of the Earth. Life has been found floating in the rarified air of the stratosphere. Microbes have been found as high as 10 miles above the ground. This environment is extremely harsh. The temperature and pressure is very low, the flux of ultraviolet light is very high, and there is nearly no water. Survival in this hostile environment inevitably raises questions of “panspermia”, which is the premise that life might have arrived on Earth from some other body... perhaps Mars. While this seems improbable, it is not ruled out. But life had to start somewhere, so the questions are still relevant, even if life started elsewhere. Of interest to us here is the understanding that some primitive forms of life can exist in an environment that would kill creatures that live closer to the Earth's surface. However, this primitive form of life wouldn't be an Alien. But it does give us some additional information on precisely how resilient Earth-based life, with our carbon and water-based biochemistry, can be.

(Source: Alien Universe, extraterrestrial Life in Our Minds and the Cosmos, by Don Lincoln).

Presence of water and oceans are one of the conditions which create life on the Earth. Photo by Elena.