How do certain microorganisms survive in extreme environments? - medical - 2023



Living at more than 100 ° C, in the waters of the Dead Sea, at the bottom of the Mariana Trench, in space, under radiation 3,000 times higher than those that are fatal to humans ... When it comes to withstanding extreme conditions, no animal or plant comes close to bacteria.

And it is that although it is true that humans are the most intelligent living beings and we have been able to develop incredible technologies, from the physical point of view, we are organisms very sensitive to environmental disturbances.

We need very specific oxygen concentrations to be able to breathe, at which temperatures rise slightly and we avoid going outside, when we submerge a few meters in a pool, our ears already hurt due to the pressure effect, radiation kills us if it is in high doses… Bacteria resist these and many other conditions, even to extreme limits.

But how do seemingly simple organisms like bacteria not only survive in extreme environments, but also develop and reproduce without problems, establishing that hostile place as their "home"? This is what we will discuss in today's article.

What are Extremophilic Bacteria?

As its name indicates, Extremophilic bacteria are those capable of surviving, growing and reproducing under extreme conditionsIn other words, they can colonize environments in which there are one (or more) physical or chemical parameters at limits that make it impossible for other life forms to develop.

There are many different extremophilic species and they are adapted to life-challenging conditions. But it is that bacteria were the first inhabitants of the Earth, so they have had plenty of time to adapt to any imaginable environment.

And it is that bacteria have been on Earth for more than 3,000 million years. Much longer than the time that plants (530 million years) or mammals (220 million years) have; not to mention the human species (250,000 years). Bacteria have had much longer for evolution to act on them and allow them to adapt to any condition.

Extremophilic bacteria are those that live in environments in which, before their discovery, it was believed that life was absolutely impossible, since no known animal or plant is able to withstand these conditions for long without dying. And bacteria not only don't die, they grow and reproduce without problems.

This adaptation is possible since over millions of years, evolution has made some species develop mechanisms and strategies to cope with these conditions so inhospitable. Because bacteria are the simplest forms of life, but this simplicity is precisely what allows them to endure so much.

How do bacteria adapt to extreme environments?

There is no place on Earth that cannot be colonized by at least one kind of bacteria. It does not matter if there is no light or oxygen, the temperatures are extremely high or low, the pressure is very high, there are practically no nutrients, there is a lot of radiation, there is a lot of acidity ... There will always be a bacterial species capable of growing there.

  • We recommend you read: "The 7 most resistant species of bacteria in the world"

To achieve this, bacteria, which are single-celled organisms, have developed some strategies to reduce the impact that these extreme conditions have on their integrity. Below we see these adaptations.

1. Synthesis of thermostable proteins

In the realm of biology, proteins are everything. They are involved in all the physiological processes that occur in our body. And this is so in all forms of life, from animals to plants, including bacteria. And one of the main reasons why living beings are so sensitive to high temperatures is because, after 50 ° C, proteins begin to denature.

This denaturation process consists in that, due to high temperatures, proteins lose their structure and, therefore, their functionality. And without functional proteins, cells inevitably begin to die.

And this happens so in all living beings except some species of bacteria such as "Pyrococcus furiosus", a microorganism whose preferred growth temperature is the boiling temperature of water, that is, 100 ° C. And it is in fact capable of surviving up to 120 ° C, much more than any other living being.

This is possible because this bacterium has adapted to synthesize thermostable proteins, molecules with a different structure from the proteins that other organisms produce and that do not "break" due to the action of high temperatures. These proteins last much longer without being denatured, and therefore the bacteria remain functional even at such high temperatures.

2. Very resistant cell membranes

The cell membrane is a structure that covers all cells, delimiting them and protecting their internal structures, that is, molecules, genetic material, proteins, lipids ... Everything. Any cell of a living being is covered by a membrane, which is quite resistant. But it has a limit.

There are many conditions that can break this membrane. And if this happens, the cell dies. High pressures and high acidity are two of the situations that have the greatest impact on the integrity of the cell membrane..

This explains why acidic substances burn us and we die if we are subjected to very high pressures, such as those found in the depths of the sea. However, some species of bacteria have been able to develop a cell membrane with a composition different from that of other living beings.

They have a very specific amount of lipids and membrane proteins that make it much more difficult to break. For this reason, there are microorganisms such as "Helicobacter pylori", capable of growing in our stomach, an incredibly acidic environment. Another example is "Shewanella benthica", a bacterium found at the bottom of the Mariana Trench, the deepest point in the ocean (11 km away), with a pressure 1,000 times greater than that at sea level.

3. Avoid crystallization of cell structures

Living beings usually die of cold when it reaches the freezing temperatures of water since crystals are formed in cell structures. We freeze because our cells do. And this happens in all organisms, except some bacteria.

There are bacteria capable of surviving and developing without problems below 0 ° C, since they have cellular mechanisms that prevent intracellular water crystallization. And the fact is that the cells are more than 70% water, so in theory, at these temperatures, it should turn into ice.

Bacteria such as "Polaromonas vacuolata" are capable of synthesizing proteins that initiate thermal and physiological processes that prevent the water inside from freezing, keeping the integrity of the cellular structures intact even at such low temperatures. This allows it to survive and colonize environments such as the waters of Antarctica. It has been seen that it can withstand temperatures of -12 ° C.

4. Increase water retention

All living things need water to survive. And bacteria are no exception. Even the toughest ones need water. Therefore, many food preservation mechanisms are based on depriving these bacteria of the water necessary to grow. Salt, for example, causes cells to lose water, so they become dehydrated and die.

Most bacteria are very sensitive to saline environments as they lead to their death. But, obviously, there are some species that the presence of salt does not affect them at all. They have mechanisms to retain water inside and prevent dehydration.

An example of this is "Haloferax volcanii", capable of surviving in perhaps one of the most extremely salty environments in the world: the Dead Sea. No other form of life can grow in it. However, this microorganism has cellular mechanisms that prevent water from being lost through osmosis (the phenomenon that explains that cells lose water if there is a lot of salt in the environment), so they do not dehydrate. So what they do is inhibit the osmosis process.

5. Mechanisms for correcting genetic damage

We say that radiation (if it is in high doses) is deadly because it is carcinogenic. And it is carcinogenic because it increases mutations in our cells, that is, alterations in their genetic material. All living beings are sensitive to radiation since they do not have strategies to "repair" this damage in the genes so quickly, so the affected cells end up dying or developing cancer.

But evidently there are bacteria capable of withstanding radiation, even at doses that would kill us in a matter of seconds. The clearest example is “Deinococcus radiodurans”, a bacterium that won the Guinness Record for “most resistant bacteria in the world”, as it is capable of surviving radiation doses 3,000 times higher than that which is fatal to other living beings.

This is possible since this bacterium has much more efficient repair mechanisms for the genetic material than those of other organisms, so although radiation damages its DNA, there are molecules that correct errors before cell viability is seen engaged. In addition, this bacterium stores several copies of its genetic material so that, in case at some point it cannot reverse the damage, it has another "saved" copy.

Bibliographic references

  • Jha, P. (2014) "Microbes Thriving in Extreme Environments: How Do They Do It?". International Journal of Applied Sciences and Biotechnology.
  • Gómez, F. (2016) “Specific work guide on Life in extreme environments”. Investigate R + D + I.
  • Goswami, S., Das, M. (2016) “Extremophiles: a Clue to Origin of Life and Biology of Other Planets”. Everyman's Science.