What is the most stable and strong life form in our world? Cockroaches are famous for their vitality - many people are convinced that they could even survive a nuclear apocalypse. Tardigrades, or water bears, are even more resilient. They can even survive in space. There is one algae living in the boiling sour springs of Yellowstone National Park. Around it is caustic water, flavored with arsenic and heavy metals. To stay alive in this deadly place, she used an unexpected trick.
What's her secret? Theft. She steals genes for survival from other life forms. And this tactic is far more common than one might think.
Most living things that live in extreme places are unicellular organisms - bacteria or archaea. These simple and ancient life forms do not have complex animal biology, but their simplicity is an advantage: they cope much better with extreme conditions.
For billions of years, they hid in the most inhospitable places - deep underground, at the bottom of the ocean, in permafrost or in boiling hot springs. They have come a long way, evolving their genes over millions or billions of years, and now they help them cope with just about anything.
But what if other, more complex creatures could just come along and steal those genes? They would have accomplished an evolutionary feat. In one fell swoop, they would have acquired the genetics that allowed them to survive in extreme places. They would get there without going through the millions of years of tedious and arduous evolution that is usually required to develop these abilities.
This is exactly what the red alga Galdieria sulphuraria did. It can be found in hot sulfur springs in Italy, Russia, Yellowstone Park in the United States and Iceland.
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Temperatures in these hot springs rise to 56 degrees Celsius. While some bacteria can live in pools at around 100 degrees, and some can cope with temperatures around 110 degrees, close to deep-sea springs, it is quite remarkable that eukaryotes are a group of more complex life forms that include animals and plants (red algae - this plant) - can live at a temperature of 56 degrees.
Most plants and animals would not be able to handle these temperatures, and for good reason. Heat leads to the destruction of chemical bonds within proteins, which leads to their collapse. This has a catastrophic effect on enzymes that catalyze the body's chemical reactions. The membranes surrounding the cell begin to leak. Upon reaching a certain temperature, the membrane collapses and the cell disintegrates.
Even more impressive, however, is the ability of algae to tolerate an acidic environment. Some hot springs have pH values between 0 and 1. Positively charged hydrogen ions, also known as protons, make a substance acidic. These charged protons interfere with proteins and enzymes inside cells, disrupting chemical reactions vital to life.
Temperatures in these hot springs rise to 56 degrees Celsius. While some bacteria can live in pools at around 100 degrees, and some can cope with temperatures around 110 degrees, close to deep-sea springs, it is quite remarkable that eukaryotes are a group of more complex life forms that include animals and plants (red algae - this plant) - can live at a temperature of 56 degrees.
Most plants and animals would not be able to handle these temperatures, and for good reason. Heat leads to the destruction of chemical bonds within proteins, which leads to their collapse. This has a catastrophic effect on enzymes that catalyze the body's chemical reactions. The membranes surrounding the cell begin to leak. Upon reaching a certain temperature, the membrane collapses and the cell disintegrates.
Even more impressive, however, is the ability of algae to tolerate an acidic environment. Some hot springs have pH values between 0 and 1. Positively charged hydrogen ions, also known as protons, make a substance acidic. These charged protons interfere with proteins and enzymes inside cells, disrupting chemical reactions vital to life.
This gene transfer phenomenon is known as "horizontal gene transfer". Typically, lifeform genes are inherited from parents. In humans, this is exactly the case: you can trace your characteristics along the branches of your family tree to the very first people.
Nevertheless, it turns out that both now and then "alien" genes of completely different species can be included in the DNA. This process is common in bacteria. Some argue that this occurs even in humans, although it is disputed.
When someone else's DNA acquires a new owner, it doesn't have to sit idly by. Instead, she can start working on the biology of the host, encouraging her to create new proteins. This can give the owner new skills and allow him to survive in new situations. The host organism can set off on a completely new evolutionary path.
In total, Schoinknecht identified 75 stolen genes from the seaweed, which it borrowed from bacteria or archaea. Not all genes give algae a clear evolutionary advantage, and the exact function of many genes is unknown. But many of them help Galdieria survive in extreme environments.
Its ability to deal with toxic chemicals like mercury and arsenic comes from genes borrowed from bacteria.
One of these genes is responsible for the "arsenic pump" that allows algae to effectively remove arsenic from cells. Other stolen genes, among other things, allow the algae to release toxic metals while extracting important metals from the environment. Other stolen genes control enzymes that allow algae to detoxify metals like mercury.
The algae have also stolen the genes that allow them to withstand high salt concentrations. Under normal circumstances, a saline environment will suck water out of the cell and kill it. But by synthesizing compounds inside the cell to equalize the "osmotic pressure", Galdieria avoids this fate.
Galdieria's ability to tolerate extremely acidic hot springs is believed to be due to its impermeability to protons. In other words, she may simply prevent acid from entering her cells. To do this, it simply includes fewer genes that code for channels in the cell membrane through which protons normally pass. These channels usually allow positively charged particles, like potassium, to pass through, which cells need, but they also allow protons to pass through.
"The adaptation to low pH appears to have been accomplished by removing any membrane transport protein from the plasma membrane that would allow protons to enter the cell," says Scheunknecht. “Most eukaryotes have multiple potassium channels in their plasma membranes, but Galdieria has only one gene that encodes a potassium channel. A narrower channel allows you to cope with high acidity."
However, these potassium channels do important work, they take up potassium or maintain a potential difference between the cell and its environment. How the algae remains healthy without potassium channels is not yet clear.
Also, no one knows how the algae copes with high heat. Scientists have been unable to identify genes that would explain this particular feature of her biology.
Bacteria and archaea, which can live at very high temperatures, have completely different proteins and membranes, but the algae has gone through more subtle changes, says Scheunknecht. He suspects that it changes the metabolism of membrane lipids at different temperature increases, but does not yet know exactly how this happens and how it allows it to adapt to heat.
It is clear that copying genes gives Galdieria a huge evolutionary advantage. While most of the unicellular red algae related to G. sulphuraria live in volcanic areas and cope with moderate heat and acids, few of its relatives can withstand as much heat, acid and toxicity as G. sulphuraria. In fact, in some places, this species accounts for up to 80-90% of life - this indicates how difficult it is for someone else to call the house of G. sulphuraria theirs.
There remains one more obvious and interesting question: how did the algae steal so many genes?
This alga lives in an environment that contains a lot of bacteria and archaea, so in a sense, it has the ability to steal genes. But scientists don't know exactly how DNA jumped from bacteria to such a different organism. To successfully get to the host, DNA must first get into the cell, and then into the nucleus - and only then incorporate itself into the host's genome.
“The best guesses at this time are that viruses could transfer genetic material from bacteria and archaea to algae. But this is pure speculation,”says Scheinknecht. “Maybe getting into a cage is the hardest step. Once inside a cell, getting into the nucleus and integrating into the genome may not be that difficult.
Horizontal gene transfer often occurs in bacteria. This is why we are having problems with antibiotic resistance. Once a resistant gene appears, it spreads rapidly among bacteria. However, it was believed that gene exchange occurs less frequently in more advanced organisms than in eukaryotes. It was believed that bacteria have special systems that allow them to accept nucleic acids, such as eukaryotes do not.
However, other examples of advanced creatures that steal genes to survive in extreme conditions have already been found. The snow algae Chloromonas brevispina, which lives in the snow and ice of Antarctica, carries genes that were probably taken from bacteria, archaea, or even fungi.
Sharp ice crystals can pierce and perforate cell membranes, so creatures living in cold climates must find a way to combat this. One way is to produce ice-binding proteins (IBPs), which are secreted in a cell that clings to ice, stopping the growth of ice crystals.
James Raymond of the University of Nevada at Las Vegas mapped the snow alga genome and found that the genes for ice-binding proteins were remarkably similar in bacteria, archaea, and fungi, suggesting that they all exchanged the ability to survive in cold conditions during the horizontal gene transfer.
“These genes are essential for survival, as they have been found in every cold-adapted algae and none in warm conditions,” says Raymond.
There are several other examples of horizontal gene transfer in eukaryotes. The tiny crustaceans living in Antarctic sea ice seem to have acquired this skill too. These Stephos longipes can live in liquid salt channels in ice.
"Field measurements have shown that C. longipes live in supercooled brines on a surface layer of ice," says Rainer Kiko, a scientist at the Institute for Polar Ecology at the University of Kiel in Germany. "Subcooled means that the temperature of this liquid is below freezing and depends on salinity."
To survive and prevent itself from freezing, molecules are present in the blood of S. longipes and other body fluids that lower the freezing point to match the water around. At the same time, crustaceans produce non-freezing proteins that prevent ice crystals from forming in the blood.
It is assumed that this protein was also obtained through horizontal gene transfer.
The beautiful monarch butterfly may also have stolen genes, but this time from a parasitic wasp.
The lustrous wasp from the Braconid family is known for introducing an egg along with a virus into a host insect. The virus's DNA hacks into the host's brain, turning it into a zombie, which then acts as an incubator for the wasp's egg. Scientists have discovered the genes of draconids in butterflies, even if these butterflies have never met wasps. They are believed to make butterflies more resistant to disease.
Eukaryotes don't just steal individual genes. Sometimes thefts are massive.
The bright green marine inhabitant Elysia chlorotica is believed to have acquired the ability to photosynthesize by eating algae. This sea slug ingests chloroplasts - organelles that carry out photosynthesis - whole and stores them in the digestive glands. When pressed and there is no algae to eat, the sea slug can survive by using the energy of sunlight to convert carbon dioxide and water into food.
One study shows that sea slugs also take genes from algae. Scientists insert fluorescent DNA markers into the algal genome to see exactly where the genes were. After feeding on algae, the sea slug acquired a gene for chloroplast regeneration.
At the same time, the cells in our body contain tiny energy-producing structures, mitochondria, that are different from the rest of our cellular structures. Mitochondria even have their own DNA.
There is a theory that mitochondria existed as independent life forms billions of years ago, but then somehow they began to be included in the cells of the first eukaryotes - perhaps the mitochondria were swallowed, but not digested. This event is believed to have occurred about 1.5 billion years ago and was a key milestone in the evolution of all higher life forms, plants and animals.
Genetic stealing may be a common evolutionary tactic. After all, she lets others do all the hard work for you while you reap the benefits. Alternatively, horizontal gene transfer can accelerate an evolutionary process that has already begun.
“An organism that has not adapted to heat or acid is unlikely to suddenly populate volcanic pools simply because it has the genes it needs,” says Scheunknecht. "But evolution is almost always a step-by-step process, and horizontal gene transfer allows for big leaps forward."
ILYA KHEL
