Life in high temperature media

1990/03/01 Urdanpilleta Iraola, Maxux Iturria: Elhuyar aldizkaria

• Biologia

If the medium is special, that is, too hot, too humid or too salty, we know that most living beings disappear. However, the information available about these environments is scarce.

However, in these unique environments we can find a few living beings:

• Salt water lakes
• In blind heads with hot mineral waters
• In deep seas
• High atmosphere
• In the snow that never disappear

Undoubtedly, the most unique are the high temperature zones.

Influence of temperature

Temperature is the parameter that most influences cell activity.

Although the temperature along the planet is moderate, we always find high temperature areas near volcanoes. Only bacteria survive more than 60ºC. Most plants and animals disappear above 37ºC. Some researchers found it interesting to know how much temperature each being can last. In this sense, Cohn conducted comprehensive studies and the most important conclusion he obtained was:

As the temperature increases, the entire taxonomic groups disappear.

From a phylogenetic point of view, living beings can be of two types:

• Eukaryotes Rule
• Prokaryotes What have no nucleus, whose only example are bacteria.

We cannot find multicircular living beings that exceed 50ºC.

Living beings that can exceed 60ºC are known as thermophiles and prokaryotes, that is, only bacteria develop at these temperatures.

But among the prokaryotes we can only find some in biotopes above 60ºC. In addition, some bacteria that live at high temperatures are not only thermophiles but also acidophiles, that is, they can live at low pH.

The most thermophilic bacterial species was isolated in 1982, giving it the name Pyrodictium. This bacteria can develop at 11ºC. Until recently it was thought that living beings could only resist until 100ºC.

Although research carried out in recent years has resulted in environments of 350ºC, it is considered that the highest temperature that living beings can withstand is between 110 and 250ºC.

Study of the best known geothermal biotopes

Natural geothermal means are an ideal means to study the ecology of microorganisms.

The pH of temperate springs in which microbial ecology has been studied is very low. This acidity is due to the formation of H ₂ SO ₄ produced by oxidation of sulphides such as H ₂ S and pyrite (FeS 2).

The sulphides are very abundant in the vicinity of the volcanoes. These sulphides oxidize rapidly in the presence of oxygen. This oxidation may be due to spontaneously oxidizing bacteria or S (sulfur). Among the bacteria that oxidize sulfur, the most common is the so-called SULFOBULUS. These sulfobulus can be found in acidic or hot media. In these areas there are few fish, but we can find some small animals.

Some thermophilic bacteria that live in geothermal media are important biochemical agents, as they participate in the cycle of elements of nature such as sulfur.

Thermostability. Internet Problem

For an organism to survive at high temperatures, the most important thing is the thermostability of the cell membrane.

Most mesophilous organisms have membranes that dissolve rapidly by increasing temperature. In the case of thermophilic organisms, they can be heated at high temperatures without the membrane losing its integrity.

The bases of membrane thermostability are listed below. The membrane of eukaryotic cells and eubacteria is formed by two layers.

In this layer the lipids are incorporated. These lipids have two aspects: one is hydrophobic and the other is hydrophilic.

The hydrophilic part is oriented out of the cell by touching the water. The hydrophobe inward, with a relatively poor indoor environment in water.

When this layer formed by lipids is heated, the hydrophobic parts become mobile, beginning to separate.

From a critical temperature, the molecules are completely separated by dividing the membrane.

However, thermophilic bacteria behave differently in increasing temperature.

It is known that the sensitivity to membrane temperature is conditioned by the proportion of lipids in fatty acids.

Unsaturated fatty acids in the membrane are much freer. Therefore these are much more sensitive to temperature.

Higher proportion of saturated fatty acids, higher membrane melting temperature.

Therefore, it is observed that in thermophilic bacteria the proportion of saturated fatty acids is much higher.

The cell is not only composed of biological membranes, but also of other macromolecular components. These ingredients are proteins and nucleic acids. Protein and nucleic acid have a specific configuration to maintain if they have activity. The structure of these macromolecules depends on the interactions that occur inside each molecule.

These interactions are relatively weak and easily broken by temperature. This is the case of classical organisms (i.e. proteins and nucleic acids).

The latest studies suggest that the electrostatic interactions that occur inside the molecule of thermophilic cases make the thermal stability of proteins high. In the case of nucleic acids, their forming is maintained through low energy interactions. Its stability is very temperature dependent.

The DNA molecule consists of two auxiliary chains, both chained. Each nucleotide present in each chain interacts with the nucleotide of the chain that precedes it by forming H (hydrogen) bridges.

These joints are broken by heat, separating the chains. Thus, the DNA molecule loses its functionality.

In thermophiles, however, due to the formation of additional joints, their integrity is not broken due to temperature.

Industrial future of thermophiles

Thermophilic organisms interest Biotechnology for two reasons:

• Because they can grow and survive in special conditions.
• Because the stability of its molecular components is very important.

Thermophilic organisms have created great curiosity because they are able to produce enzymes that can work at high temperatures. These thermophilic enzymes are more stable than conventional enzymes at moderate temperatures. If an industrial process consists of thermophilic enzymes, its development will be faster the higher the ambient temperature.

Use of thermophiles

They are widely used in anaerobic planks of debuggers. They are used for the production of the following compounds:

• Ethanol
• Alcoholic fuels
• Acetic acid
• Antibiotics

In addition to microorganisms, the enzymes they produce are very important in the industry, as they significantly reduce process costs.