Living at more than 100 ° C, in the waters of the Dead Sea, at the bottom of the Mariana Trench, in space, under radiation 3000 times higher than those that are fatal to humans … When it comes to coping with conditions extreme, no animals or plants come close to bacteria .
And is that although it is true that humans are the most intelligent living beings and we have been able to develop extraordinary technologies, from a physical point of view, we are very sensitive organisms to environmental disturbances.
We need very specific concentrations of oxygen to be able to breathe, in which temperatures rise slightly and we avoid going outside, when we dive a few meters into a pool, our ears already hurt us due to the effect of pressure, radiation kills us if it is in high doses ret Bacteria resist these and many other conditions, even at extreme limits.
But how seemingly simple organisms like bacteria not only survive in extreme environments, but also develop and reproduce smoothly, making that hostile place their “home”? This is what we will discuss in today’s article.
What are extremophilic bacteria?
As its name suggests, Extremophilic Bacteria are those capable of surviving, growing, and multiplying in extreme conditions . In other words, they can colonize environments in which there is one (or more) physical or chemical parameters at the boundaries that make it impossible for other forms of life to develop.
There are many different types of extremophiles and they are adapted to life-threatening conditions. But bacteria were the first inhabitants of the Earth, so they had plenty of time to adapt to any environment imaginable.
And it’s that bacteria have been on Earth for over 3,000 million years. Much longer than the time plants (530 million years) or mammals (220 million years) have; not to mention 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, life was believed to be absolutely impossible, as no known animal or plant is able to withstand these conditions for a long time without dying. And bacteria not only do not die, but grow and reproduce without problems.
This adaptation has been possible for millions of years, evolution has led some species to develop mechanisms and strategies to cope with these unfavorable conditions. Because bacteria are the simplest forms of life, but that simplicity is exactly what allows them to be so resistant.
How do bacteria adapt to extreme environments?
There is no place on Earth that can not be colonized by at least one type 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 is 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.
To achieve this, bacteria, which are unicellular organisms, have developed several strategies to reduce the impact that these extreme conditions have on their integrity. We see these adaptations below.
1. Synthesis of thermostable proteins
In the field of biology, proteins are everything. They are involved in all the physiological processes that take place in our body. And so it is in all forms of life, from animals to plants, including bacteria. And one of the main reasons why living things are so sensitive to high temperatures is because, after 50 ° C, proteins begin to become unnatural.
This process of denaturation consists in the fact that, due to high temperatures, proteins lose their structure and, consequently, their functionality. And without functional proteins, cells inevitably begin to die.
And this is the case for all living beings except some species of bacteria like “Pyrococcus furiosus”, a microorganism whose preferred growth temperature is that of boiling water, namely 100 ° C. And in fact it is capable of survive up to 120 ° C , far more than any other living thing.
This is possible because this bacterium is adapted to synthesize thermostable proteins, molecules with a different structure from that of proteins produced by other organisms and which do not “break down” due to the action of high temperatures. These proteins last much longer without being unnatural, and that is why bacteria remain functional even at such high temperatures.
2. Highly resistant cell membrane
The cell membrane is a structure that covers all cells, limiting them and protecting their internal structures, namely molecules, genetic material, proteins, lipids … Everything. Every cell of a living being is covered by a membrane, which is quite resistant. But there is a limit.
There are many conditions that can damage this membrane. And if that happens, the cell dies. High pressures and high acidity are two of the situations that have the greatest impact on cell membrane integrity. .
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 managed to develop a cell membrane with a different composition from that of other living beings.
They have a very specific amount of membrane lipids and proteins that make it much harder to break down. For this reason, there are microorganisms such as “Helicobacter pylori”, capable of growing in our stomach, an extremely 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 things usually die from the cold when they reach freezing temperatures as crystals form in cell structures. We freeze because our cells do. And it happens in all organisms except a few bacteria.
There are bacteria capable of surviving and growing smoothly below 0 ° C , as they have cellular mechanisms that prevent the crystallization of intracellular water. And the fact is that the cells are more than 70% water, so in theory, at these temperatures, it should turn to ice.
Bacteria such as “Polaromonas vacuolata” are able to synthesize proteins that initiate thermal and physiological processes that prevent water freezing inside, keeping the integrity of 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 most difficult ones need water. Therefore, many food storage mechanisms are based on depriving these bacteria of the water they need to grow. Salt, for example, causes cells to lose water, so they dehydrate 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 at all. They have mechanisms to keep 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 loss through osmosis (a phenomenon that explains that cells lose water if there is too much salt in the environment), so they do not become dehydrated. So what they do is hinder 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, namely changes in their genetic material. All living things are sensitive to radiation as they have no strategy to “repair” this damage to the genes so quickly, so the affected cells end up dying or developing cancer.
But there are definitely bacteria capable of withstanding radiation even in doses that would kill us within seconds. The clearest example is “Deinococcus radiodurans”, a bacterium that won the Guinness World Record for “the most resistant bacteria in the world”, as it is capable of surviving radiation doses 3,000 times higher than what is fatal to other living beings.
This is possible because this bacterium has much more efficient mechanisms for repairing genetic material than those of other organisms, so although radiation damages its DNA, there are molecules that correct errors before cell stability is involved. Moreover, this bacterium stores several copies of its genetic material so that, in the event that at one point it cannot reverse the damage, it has another “stored” copy.