Archaea

Life at the Extreme

Many archaeans thrive in conditions that would kill other creatures: boiling water, super-salty pools, sulfur-spewing volcanic vents, acidic water and deep in Antarctic ice. These types of archaea are often labeled "extremophiles," meaning creatures that love extreme conditions.

pyrodictium

Archaeans have been found that can live in temperatures above 212°F (100°C). In contrast, no known eukaryotes can survive over 140°F (60°C). Other archaeans have been found in an Antarctic lake with a surface that is permanently frozen.

How do these extremophiles do it? They make a variety of protective molecules and enzymes (en-zimes). For example, some archaeans live in highly acidic environments. If the acid got into the archaeal cells, it would destroy their DNA, so they have to keep it out. But the defensive molecules on their cellular surfaces do come into contact with the acid and are uniquely designed not to break apart in it. Archaeans that live in very salty water are able to keep all the fluid from dissolving out of their cells by producing or pulling in from the outside solutes such as potassium chloride that balance the inside of the cells with the salty water outside. Other enzymes allow other achaeans to tolerate extreme hot or cold.

Not all the archaea are extremophiles. Many live in more ordinary temperatures and conditions. For example, scientists can find archaeans alongside bacteria and algae floating about in the open ocean. Some archaeans even live in your guts.

 

Archaea

There are three main types of archaea: the crenarchaeota (kren-are-key-oh-ta), which are characterized by their ability to tolerate extremes in temperature and acidity. The euryarchaeota (you-ree-are-key-oh-ta), which include methane-producers and salt-lovers; and the korarchaeota (core-are-key-oh-ta), a catch-all group for archaeans about which very little is known. Among these three main types of archaea are some subtypes, which include:

archaeoglobus

Methanogens (meth-an-oh-jins) — archaeans that produce methane gas as a waste product of their "digestion," or process of making energy.

Halophiles (hal-oh-files) — those archaeans that live in salty environments.

Thermophiles (ther-mo-files) — the archaeans that live at extremely hot temperatures.

Psychrophiles (sigh-crow-files) — those that live at unusually cold temperatures.

 

pyrococcusArchaea look and act a lot like bacteria. So much so that until the late 1970s, scientists assumed they were a kind of “weird” bacteria.

Then microbiologist Carl Woese devised an ingenious method of comparing genetic information showing that they could not rightly be called bacteria at all. Their genetic recipe is too different.

So different Woese decided they deserved their own special branch on the great family tree of life, a branch he dubbed the Archaea.

The Extremists

ice

gsaltlake

vent

lonestar

 

 

 

 

sulfur

Archaea can be found in many"extreme environments": highly sulfurous lakes (right); ice (top left); Utah‘s Great Salt Lake (above middle); and hot geysers like the Lonestar (above middle); and in undersea hydrothermal vents (above right).

In addition to superheated waters, archaea have been found in acid-laden streams around old mines, in frigid Antarctic ice and in the super-salty waters of the Dead Sea. A number of other extreme-living bacterial species also enjoy these conditions, too, such as the community of cyanobacteria and bacteria shown above.

 

  • Thermophiles like unusually hot temperatures. A few species have been found to survive even above 110 degrees Celsius (water boils at 100 degrees Celsius).

  • Psychrophiles like extremely cold temperatures (even down to -10 degrees Celsius).

  • Halophiles thrive in unusually salty habitats. Some can thrive in water that’s 9% salt; sea water contains only 0.9% salt.
  • Acidophiles prefer acidic conditions; Alkaliphiles prefer very alkaline environs.

Archaea that populate extreme environments (along with some of their bacterial cousins) have developed some clever tricks and tools to do so. For example, they produce special enzymes that help keep all the parts of their cells intact even in conditions that would have our human skin falling apart.

Repair DNA

Developing tricks and tools to keep their enzymes in order is one way thermophiles survive. They also use techniques to keep their DNA from falling apart under intense heat. Like proteins, the parts of the long, spiral ladder-shaped DNA molecule start to unravel and break apart under high heat. One way thermophiles keep that from happening is with a helper enzyme called "reverse DNA gyrase" <jeye-race>. This enzyme makes DNA coil up and twist upon itself in a certain way that makes the DNA more stable in high heat. (If you’ve ever seen a telephone handset cord that gets twisted and bunched up on itself, then you know what DNA coiling is like, only coiled up DNA is thousands of times more tightly twisted and bunched.) Microbes that live at normal temperatures have regular "DNA gyrase" instead, which also makes their DNA coil up, but in a different, looser way.

Thermophiles also have lots of DNA binding proteins. These binding proteins do just what their name suggests, running around gluing the pieces and parts of the DNA molecule back together when they start to come undone, much like the chaperonin proteins discussed above.

Holding it All Together

Thermotoga

Of course, tools that keep the enzymes, DNA and other inside parts of the cell from breaking up will do no good if the outside or surface of the cell is falling apart. So these heat-loving creatures have cell membranes—the rubbery lining just inside the cell wall that surrounds the cell fluid—that are formed differently than those of microbes living at normal temperatures. Normal temperature microbes have membranes that are formed by two layers of molecules called lipids which join together to create what’s called a bilayer (for a picture of what a lipid bilayer looks like, see this page). In thermophiles, the parts of each lipid layer that point inward are chemically glued together so that instead of a bilayer that could be pulled apart in intense heat, thermophiles have a thick single or monolayer.

There’s a lot that scientists still are learning about how these amazing heat-loving microbes live happily at such high temperatures. They may well have other tools and tricks that we don’t know about yet. The more we learn, the better for us because some of these techniques and tools could become useful products for us. For example, an extremozyme called Taq <tack> from one thermophilic bacterium is what makes DNA testing and DNA fingerprinting possible. Thanks in part to Taq, scientists have been able to sequence the entire human genome—everything on the whole humongous human DNA molecule—and the genomes of lots of microbes and other living things, too.

Types of Archaea

There are three main types of archaea: the crenarchaeota (kren-are-key-oh-ta), which are characterized by their ability to tolerate extremes in temperature and acidity. The euryarchaeota (you-ree-are-key-oh-ta), which include methane-producers and salt-lovers; and the korarchaeota (core-are-key-oh-ta), a catch-all group for archaeans about which very little is known. Among these three main types of archaea are some subtypes, which include:

archaeoglobus

Methanogens (meth-an-oh-jins) — archaeans that produce methane gas as a waste product of their "digestion," or process of making energy.

Halophiles (hal-oh-files) — those archaeans that live in salty environments.

Thermophiles (ther-mo-files) — the archaeans that live at extremely hot temperatures.

Psychrophiles (sigh-crow-files) — those that live at unusually cold temperatures.

pyrococcus

Archaea look and act a lot like bacteria. So much so that until the late 1970s, scientists assumed they were a kind of “weird” bacteria.

Then microbiologist Carl Woese devised an ingenious method of comparing genetic information showing that they could not rightly be called bacteria at all. Their genetic recipe is too different.

So different Woese decided they deserved their own special branch on the great family tree of life, a branch he dubbed the Archaea.

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