We cannot enter the "forbidden zone of life", but they live tenaciously here

In nature, there are some environments where ordinary organisms cannot survive, such as high temperature, low temperature, high acid, high alkali, high salt, high pressure, high radiation, etc.

However, even in these extreme environments that are generally considered to be forbidden zones for life, there are still some microorganisms that live tenaciously. We call these microorganisms extreme environment microorganisms or simply extreme microorganisms.

Today, let us get to know these tenacious little guys.

01

Psychrophilic bacteria

There are some psychrophilic microorganisms living in the Earth's Arctic and Antarctic regions, icehouses, high mountains covered with snow all year round, deep seas and frozen areas. Obligate psychrophiles are adapted to living in an environment below 20℃ and will die if the temperature is above 20℃.

Antarctic iceberg. Copyright image, no permission to reprint

There is a type of obligate psychrophile that stops synthesizing proteins when the temperature exceeds 22°C.

The cell membrane of obligate psychrophiles contains a large amount of unsaturated fatty acids, and the amount increases as the temperature decreases, thus ensuring the fluidity of the membrane at low temperatures. In this way, the cells can continuously absorb nutrients from the external environment at low temperatures.

Facultative psychrophilic bacteria have a wide temperature range of growth and can survive at temperatures as high as 30°C. Psychrophilic microorganisms are the root cause of the spoilage of low-temperature stored foods.

02

Thermophiles

Thermophiles are commonly known as high-temperature bacteria and are widely distributed in hot springs, compost, geothermal soil, volcanic areas, and submarine volcanic areas. The most suitable growth temperature for facultative thermophiles is between 50 and 65°C, while the most suitable growth temperature for obligate thermophiles is between 65 and 70°C.

In Iceland, there is a thermophilic bacterium that can grow in hot springs at 98°C. In the sulfur-containing hot springs of Yellowstone National Park in the United States, a thermophilic facultative autotrophic bacterium, Sulfolobus acidocaldarius, was isolated. They can grow at temperatures above 90°C. In recent years, this bacterium has received widespread attention and can be used for bacterial leaching of minerals, desulfurization of petroleum and coal.

Geothermal area. Copyright image, no permission to reprint

In some sludge, hot springs and deep-sea geothermal water, there live thermophilic bacteria that can produce methane. The environment they live in has high temperature, high salt concentration and very high pressure, making them difficult to isolate and culture in the laboratory.

Thermophilic fungi are often found in hot environments such as compost piles, haystacks and woodchip piles , where they help degrade some organic matter.

In the fermentation industry, thermophilic bacteria can be used to produce a variety of enzyme preparations, such as cellulase, protease, amylase, lipase, inulinase, etc. The enzyme preparations produced by these microorganisms have good thermal stability, high catalytic reaction rate, and are easy to store at room temperature.

In recent years, one of the most striking achievements in the study of thermophiles is the use of the heat-resistant Taq DNA polymerase from Thermus aquaticus in genetic research and genetic engineering research as well as the wide application of genetic technology.

03

Acidophilus

Acidophiles are distributed in acidic mineral water, acidic hot springs, etc. Among them, Acidithiobacillus is a bacterium that can grow chemoautotrophically and chemoheterotrophically, and its optimal growth environment is a pH value between 3.0 and 3.5.

For example, Thiobacillus thiooxidans can survive in an environment with a pH value below 0.5, and the obligate autotrophic acidophilic Thiobacillus ferrooxidans can oxidize sulfur and iron and produce sulfuric acid. Both of these bacteria are extreme acidophiles.

Iceland hot springs. Copyright image, no permission to reprint

In an acidic environment, there are also some acidophilic and thermophilic acidophilic acidithiobacillus, which grow at the maximum rate at 60-65℃ and pH 3-4. This bacterium can use carbohydrates or amino acids as a nutrient source.

There is another microorganism that also grows and reproduces in acidic and hot environments. It is called acidophilic thermoplasma. Its optimal growth temperature is 59°C and its optimal pH is around 2. It has no cell walls and its nutritional requirements are quite complex. It must use yeast paste as a nutrient matrix and must have natural organic nutrients to grow.

In addition, there are many acidophilic eukaryotic microorganisms living in acidic environments, such as elliptical yeast, red yeast, etc. There is a kind of cephalosporium that needs to grow in sulfuric acid with a concentration of more than 10% and requires the culture medium to contain 4% copper sulfate. It is the most acid-resistant microorganism discovered so far.

For many years, acidophilic bacteria have been widely used in bacterial leaching of metals such as copper. In addition, people are also trying to use Thiobacillus to decompose phosphate rock powder and increase its fertilizer effect by increasing its solubility.

04

Alkaliphilic bacteria

In alkaline lakes and some alkaline environments, and even in some neutral environments, alkaliphilic microorganisms can be isolated. Alkaliphilic microorganisms can grow under conditions of pH 11-12, but cannot grow under neutral pH conditions. For example, this is the case with bacteria such as Bacillus pasteurianus and Bacillus alkaliphilus.

Alkali Beach. Copyrighted image, unauthorized reproduction

A yellow bacterium was isolated from a high-pH alkaline spring that grows well at pH 11.4.

In the eutrophic waters of Lime Lake, many cyanobacteria are also alkaliphiles, and their optimal growth pH is between 9 and 10. One type of algae can even grow under strong alkaline conditions of pH 13, which is the microorganism with the highest alkalinity resistance discovered so far.

In recent years, people have also discovered alkaliphilic bacteria that can perform photosynthesis. In the fermentation industry, alkaliphilic bacteria can be used as production bacteria for many enzyme preparations. For example, the elastase produced by alkaliphilic Bacillus is suitable for acting on elastin, and the activity of cleaving this protein can be greatly improved under high pH conditions.

Proteases produced by alkaliphilic bacteria have the advantages of high catalytic activity and strong thermal stability under alkaline conditions, and are often used as additives in detergents.

There is also xylanase produced by alkalophilic Bacillus that can hydrolyze xylan to produce xylose and oligosaccharides, so it can be used to treat artificial fiber waste, while the oligosaccharides produced by alkaline β-mannanase degrading mannan can be used as an additive for health products.

05

Halophiles

Halophiles are usually found in salt fields, salt lakes, pickled products and the world-famous Dead Sea. Halophiles can grow in environments with a salt concentration of 15% to 20%, and some can even grow in 32% salt water.

Extreme halophiles include Halobacterium and Halococcus, which belong to the archaea. Halobacterium cells contain red pigments, so when they grow in large numbers in salt lakes and the Dead Sea, they make these environments appear red.

Some halophilic bacteria have purple membranes in their cells that contain a protein called bacteriorhodopsin, which absorbs energy from sunlight.

Salt marsh. Copyright image, no permission to reprint

Halophilic bacteria can cause food spoilage and food poisoning. Vibrio parahaemolyticus is a widely distributed marine bacterium and one of the main bacteria that cause food poisoning. It causes disease by contaminating seafood, pickles, roast goose, etc.

But they have actually made contributions in many fields - halophilic bacteria can be used to produce extracellular polysaccharides, polyhydroxybutyric acid (PHB), edible proteins, seasonings, health food enhancers, enzyme protectants, computer memory, etc. They can also be used for seawater desalination, saline-alkali land transformation and utilization, and energy development.

06

Barophiles

There are also some barotropic microorganisms distributed in the deep sea and deep oil wells. The pressure in their living environment reaches more than one thousand atmospheres, but they cannot survive under normal pressure. Someone once isolated barotropic bacteria at a depth of 10,897 meters on the seabed near the Philippines in the Pacific Ocean.

Barophiles that are resistant to high temperatures and anaerobic growth are expected to be used to increase gas pressure in oil wells and reduce crude oil viscosity, thereby improving recovery rates.

Copyright image, no permission to reprint

It’s incredible, right? In those barren lands where no grass grows, there actually live these microorganisms that are invisible to the naked eye.

Not only that, maybe one day, with the ingenuity of scientific researchers, these strong little guys can become our little helpers!

Produced by | Science Popularization China

Author｜Guanshiruwei Team

Producer｜China Science Expo

Submitted by: Computer Information Network Center, Chinese Academy of Sciences

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