Extreme ecosystems are those in which living conditions are such that they pose a challenge to most organisms. They cover environments with very high or low temperatures, low humidity or nutrients and high pressure, irradiation, pH or salts, among others. Although for a long time it was thought that life in these environments was not possible, today we know that life is making its way with an unsuspected momentum and that the sterile environments on our planet are a very rare exception. Despite the imaginative resources developed by the organisms that live in these ecosystems to adapt to them, the environmental pressures to which they are subjected as a consequence of global change are leading them to a compromised position, getting closer and closer to the limit of their survival.
Yellowstone’s Great Prismatic Spring: Thermophilic Organisms
Thermophilic organisms are those that are capable of surviving in ecosystems subjected to very high temperatures. In my opinion, the most iconic example of these ecosystems is the great prismatic spring of Yellowstone. Surely you have ever seen a photo of her! It is this smoky circular lake with rings of concentric colors that go from deep blue in the center to red at the outer edge, and it stinks of hard-boiled eggs, although that detail is not conveyed by the photos.
I was very surprised when I found out that both the large prismatic fountain and the more than 10,000 fumaroles and geysers found in the park are the visible face of the caldera of a very shallow volcano located at ground level that occupies much of the park. Two things are necessary to create these hydrothermal formations: heat, which comes from volcanic magma, and a lot of water, which percolates into the subsoil through cracks in the permeable rocks, and which comes from rain or snow from the Yellowstone Plateau. As the water gets closer to the magma, it gets hotter and hotter, until there comes a time when it exceeds the boiling point, but instead of going into a gaseous state, it remains in a liquid state due to the enormous pressure at which it is subjected This super-hot water is very thin and rises to the surface while cooler water sinks, creating convection currents that form the natural pumping system of the park’s hydrothermal vents.
And one would think: well, that water at those temperatures must be sterilized. What organism could live in those conditions? Until the 1960s it was thought that none, but in 1964 a microbiologist named Thomas Brock identified cyanobacteria in these steaming waters, and this changed the prevailing idea of the time that microorganisms cannot live in extreme environments and life began to be found in conditions extremes of pH, cold, heat and aridity. Returning to the prismatic source, it is precisely microbial populations adapted to different temperatures that create such impressively colored concentric circles, and not mineral deposits, as originally thought.
The main threat to these areas is the overexploitation of resources such as oil, gas or subsoil water that involves drilling on the surface. Fortunately, decades ago the pertinent authorities identified this risk and since 1994 the development of these areas has been limited. This protection has allowed hundreds of investigations to be carried out on heat-resistant microorganisms in the park’s thermal areas, leading to key medical, forensic and commercial advances for our society today. Without going any further, it was in these thermophilic microorganisms that the enzyme TAQ polymerase was originally found, which makes it possible to carry out the famous PCR that has been vital in our fight against the coronavirus. That’s how important environmental conservation is and that’s how important scientific research is.
The salt flats of Alicante and the Dead Sea: Halophilic organisms
Halophilic organisms are capable of living in highly saline environments. Organisms that are not adapted to these conditions cannot survive in these environments because they die of dehydration, since the difference in the concentration of salts between the inside and outside of their cells causes the water inside the cells to tend to come out, for what they dehydrate and die. However, in halophilic organisms this does not occur thanks to various morphological or physiological adaptations that we will review below.
Taking into account that the salinity of seas and oceans is around 3%, isn’t it amazing to know that some archaea have been found in the Alicante salt flats that can tolerate a salinity of up to 34%? And how do they do it? Well, halophilic microorganisms accumulate inside a solute compatible with cell function as ions or organic compounds and also store it in special structures such as vacuoles. In this way, its concentration inside is higher than outside and this makes the water remain inside the cells avoiding dehydration.
Plants are also capable of adapting to these extreme environments: A halophyte plant can maintain an internal salt concentration compatible with life through three main mechanisms: the first is by excreting excess salt through structures such as salt glands or trichomes, the second is by concentrating the salts in the tissues of its leaves that later die and fall, and the third is by diluting the concentration of salts in the water retained in a special tissue called aquiferous parenchyma.
The most iconic example that comes to mind of this type of environment is the Dead Sea, between Israel and Jordan, whose salinity level varies between 28 and 32%, depending on the depth. This is precisely the characteristic that gives rise to its name, since it was thought that no organism could live in that environment. And although it is true that there is not a single species of fish or amphibian in its waters, there is a specially adapted species of crustacean that is brine shrimp and certain species of pelicans and storks that feed on them, as well as bacteria, archaea and halophilic viruses.
And the million dollar question is: why is the Dead Sea so salty? Well, the first thing I have to point out is that it is not a sea, but a lake. But not just any lake, but an endorheic lake, which means that several rivers and streams flow into it, but none drain out, so the minerals that reach the lake stay there forever. Other factors such as the fact that it is located more than 400 meters below sea level and that the hot desert climate favors the evaporation of its waters, converge to make the Dead Sea what it is. In this way, the salinity of the lake increases each year as minerals accumulate, so much so that the density of its waters is so high that it does not allow the human body to sink.
Due to the increase in temperature due to climate change and the extraction of water for irrigation, the water level of the Dead Sea is reduced by one meter per year. In addition, several Israeli and Jordanian companies extract the minerals from their waters for the development of an important economic activity, and for that it is also necessary to artificially evaporate the water. All these factors reduce the level of the waters of the Dead Sea every year and threaten its stability, so hypersaline ecosystems will also need our protection to overcome the changes that the near future brings.
Rio Tinto: Acidophilus organisms
The Tinto River (Huelva) is located in an area rich in a mineral composed of iron and sulfur that has been exploited in these mines for more than 5,000 years: pyrite. The Tinto River presents particularly inhospitable waters to harbor life since it has a high concentration of heavy metals, iron and sulfur compounds, and a pH as acidic as the inside of our stomach. However, and contrary to all logic, these river waters teem with life.
Although some eukaryotic microorganisms such as algae and fungi survive in these conditions, the organisms that really proliferate in this hostile environment and the protagonists of this story are a type of unicellular organisms without a defined nucleus called chemolithoautotrophs, which could be translated as eating organisms. of stones. And they have such a curious name because they do not need any organic substrate for their nutrition, but instead obtain their energy from the oxidation of inorganic compounds, mainly pyrite.
An aside to this story: I don’t know what explanation they gave you when you asked why the waters of this river were reddish, but they told me it was due to the iron content of the minerals in the mine. Well, it seems that the minerals per se are not responsible for the coloration of the river, but rather the chemolithoautotrophs are the ones that, by metabolizing the pyrite, produce as a secondary component the ferric ion that gives that reddish color to the waters, in addition to protons and sulfate that acidify the water to a pH of 2. The fact that a biological process is behind the acidity of the water is what keeps the pH stable and is not diluted by rainy season precipitation or concentrate with the summer drought.
Therefore, it is these extraordinary organisms that have made the Tinto River an iconic enclave, determining both its acidity and its colouring. But the thing does not stop there, but, in addition, these microorganisms are resistant to ultraviolet radiation and can live without oxygen in the river sediments, which would allow them to survive on a planet without an ozone layer. This characteristic, added to the fact that they incredibly do not need organic matter to live, has drawn the attention of NASA to study the origins of life on earth when our planet was very different from how we know it today. To add even more interest to the subject, it turns out that NASA’s opportunity probe found in the soil of Mars a mineral produced by chemolithoautotrophs when they carry out metabolism in acidic waters. Therefore, and in the absence of further evidence, this mineral could be considered an indicator of a biological process outside the earth.
One would think that an ecosystem so limited in space, singular, and valuable from the scientific, economic, environmental and tourist point of view, surely it is duly pampered and protected. Well, not for those. It turns out that Ecologists in Action has spent years denouncing the different points of contamination of the river by water spills. From a dye factory located on the river bank that changes the color of its waters, to leaks from the Nerva toxic landfill, passing through untreated fecal water from the municipalities through which the river passes. The documentary “Tinto” by the Triángulo Obtuso collective collects these complaints. For me in particular, the fact that there is so little political will to solve such a local problem gives me little hope that we can meet the challenges of global change, but there is nothing left but to hope and take small individual steps. that promote environmental protection.
*****
This article is sent to us Lourdes Morillas: PhD in ecology from the Pablo de Olavide University of Seville, currently working as a researcher at the University of Lisbon. In recent years she has specialized in the study of soil processes in Mediterranean ecosystems in a context of global change. On her website mednchange.weebly.com she writes about the course of her current project, Med-N-Change. You can also follow her on Twitter: @Morillas_L the en @MedNChange.
If you have an interesting article and you want us to publish it in Naukas as a guest contributor, you can contact us.