The invisible world
Microbes have great adaptability. Take extremophiles. Extremo - because they live in extreme conditions and -phile after the Greek philos meaning "lover of". They may be the oldest organisms on Earth. And with their incredible survival skills they push the limits of life. Not only in our search for extraterrestrial life, but also in the field of biotechnological solutions for a more sustainable future.
Our planet is about 4.5 billion years old. Life originated about 3.6 billion years ago. For the first 2 billion years, life was unicellular, and often extremophile. The current conditions on Earth, which are habitable and “normal” to us, used to be very different. The young Earth was a lot more extreme. We would never survive there, but extremophiles could. For much of Earth’s history, extremophiles have probably been the most common forms of life.
Due to their “extreme” diversity, microbes inhabit a much larger part of the earth’s surface than humans. Deep underground, on the sea bed, under the Antarctic ice and even inside volcanoes. Every place is unique, but there is always an extremophile who has made it home. There are extremophiles that live at high temperatures (thermophiles), low temperatures (psychrophiles), high pressure (barophiles), low acidity (acidophiles), high acidity (alkaliphiles) and high salinity (halophiles). They are often adapted to several extremes at the same time. This is called polyextremophile. Think, for example, of microbes that live on the deep seabed where there is a high pressure and a low temperature at the same time.
The thermophilic archaea (Methanopyrus kandleri) are onecellular organisms that seek out extremes. It lives in hydrothermal deep-sea vents at temperatures up to 122 ° C. We live at sea level with about 1 bar of pressure, but the barophilic archaea Thermococcus piezophilus survives a pressure of almost 1300 bar under experimental conditions. This is higher than the pressure at the deepest point in the ocean, the Mariana Trough (1100 bar). Without a doubt the most extreme extremophile is the bacterium Deinococcus radiodurans. It survives gamma rays up to 50,000 Gy (Gray). Humans can’t even survive 5 Gy.
Extremophiles often have the most unique biological solutions. For example, special DNA repair mechanisms or extra DNA copies to protect against harmful radiation. Psychrophilic microbes have a lot of unsaturated fats on their cell membranes. These fats remain liquid at low temperatures, which keeps the cell membrane flexible. Halophilic organisms live in a world where the high salt concentration normally draws the moisture out of their cells. But with special substances in their cells, they counter this osmosis. In some cases, even the structure of their DNA is different. The DNA of thermophiles has extra hydrogen bonds between the two strands so that the DNA does not disintegrate at high temperatures.
Biotechnology uses many enzymes from extremophiles. Enzymes are very picky. Ours work best at 37°C and a neutral pH. But those of the archaea Pyrococcus furiosus, which naturally lives at 70°C, work best around that temperature and won’t survive 37°C. In the food industry, thermophilic enzymes play an important role in the many baking processes. Low temperatures are also sometimes desirable. For example, lactase (an enzyme that breaks down lactose) from psychrophilic organisms is used in making lactose-free milk. This enzyme still does its job while the milk is in the refrigerator. Detergents, very basic (high acidity) products, are also full of extremophilic enzymes. The enzymes of alkaliphiles break down the dirt on clothes even at a high pH.
One of the major applications of extremophilic enzymes can be found in the laboratory. Namely in PCR, or “polymerase chain reaction”. PCR is widely used to propagate DNA and is crucial for genetic laboratory research, diagnostic testing in medical science, and even identifying criminals. PCR depends on the enzyme polymerase that copies the pieces of DNA. This process takes place at high temperatures. And so a polymerase is needed that can withstand this. The most famous is called Taq polymerase, named after the thermophile Thermus aquaticus from which it originates.
