The thermophiles They are a subtype of Extremophilic organisms that are characterized by tolerating high temperatures, between 50 ° C and 75 ° C, either because these temperature values are maintained in these extreme environments, or because they are frequently reached.
Thermophilic organisms are generally bacteria or archaea, however, there are metazoans (eukaryotic organisms that are heterotrophic and tissue), which also develop in hot places.
Marine organisms are also known that, associated in symbiosis with thermophilic bacteria, can adapt to these high temperatures and that have also developed biochemical mechanisms such as modified hemoglobin, high blood volume, among others, that allow them to tolerate the toxicity of sulfides and compounds. sulfur.
It is believed that thermophilic prokaryotes were the first simple cells in the evolution of life and that they inhabited places with volcanic activity and geysers in the oceans.
Examples of this type of thermophilic organisms are those that live in the vicinity of hydrothermal vents or vents at the bottom of the oceans, such as methanogenic (methane-producing) bacteria and annelid Riftia pachyptila.
The main habitats where thermophiles can be found are:
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Temperature is one of the key environmental factors that determines the growth and survival of living things. Each species has a range of temperatures between which it can survive, however, it has optimal growth and development at specific temperatures..
The growth rate of each organism versus the temperature can be graphically expressed, obtaining the values corresponding to the important critical temperatures (minimum, optimum and maximum)..
At the minimum growth temperatures of an organism, a decrease in the fluidity of the cell membrane occurs and the processes of transport and exchange of materials, such as the entry of nutrients and the exit of toxic substances, can be stopped..
Between the minimum temperature and the optimum temperature, the growth rate of microorganisms increases.
At the optimal temperature, metabolic reactions occur with the highest possible efficiency.
Above the optimal temperature, a decrease in growth rate occurs to the maximum temperature that each organism can tolerate.
At these high temperatures, structural and functional proteins such as enzymes are denatured and inactivated, as they lose their geometric configuration and particular spatial configuration, the cytoplasmic membrane breaks and thermal lysis or rupture occurs due to the effect of heat..
Each microorganism has its minimum, optimal and maximum operating and development temperatures. Thermophiles have exceptionally high values at these three temperatures.
Thermophilic organisms can be divided into three broad categories:
Hydrothermal sites are surprisingly common and widely distributed. They can be broadly divided into those that are associated with volcanic areas and those that are not..
Hydrothermal environments with the highest temperatures are generally associated with volcanic features (calderas, faults, plate tectonic boundaries, back arc basins), which allow magma to rise to a depth where it can directly interact with groundwater deep.
Hot spots are also often accompanied by other characteristics that make life difficult to develop, such as extreme pH values, organic matter, chemical composition and salinity..
Inhabitants of terrestrial hydrothermal environments, therefore, survive in the presence of various extreme conditions. These organisms are known as polyextremophiles..
Organisms belonging to all three domains (eukaryotes, bacterial, and archaea) have been identified in terrestrial hydrothermal environments. The diversity of these organisms is determined mainly by temperature.
While a diverse range of bacterial species inhabit moderately thermophilic environments, photoautotrophs can come to dominate the microbial community and form macroscopic “mat” or “carpet”-like structures..
These “photosynthetic mats” are present on the surface of most neutral and alkaline hot springs (pH greater than 7.0) at temperatures between 40-71 ° C, with cyanobacteria established as the main dominant producers..
Above 55 ° C, photosynthetic mats are predominantly inhabited by single-celled cyanobacteria such as Synechococcus sp.
Photosynthetic microbial mats can also be predominantly inhabited by bacteria of the genera Chloroflexus Y Roseiflexus, both members of the order Chloroflexales.
When associated with cyanobacteria, the species of Chloreflexus Y Roseiflexus grow optimally under photoheterotrophic conditions.
If the pH is acidic, the genera are common Acidiosphaera, Acidiphilium, Desulfotomaculum, Hydrogenobaculum, Methylokorus, Sulfobacillus Thermoanaerobacter, Thermodesulfobium Y Thermodesulfator.
In hyperthermophilic sources (between 72-98 ° C) it is known that photosynthesis does not occur, which allows the predominance of chemolytoautotrophic bacteria.
These organisms belong to the phylum Aquificae and are cosmopolitan; can oxidize hydrogen or molecular sulfur with oxygen as an electron acceptor and fix carbon via the reducing tricarboxylic acid (rTCA) pathway.
Most of the cultivated and uncultivated archaea identified in neutral and alkaline thermal environments belong to the phylum Crenarchaeota..
Species like Thermofilum pendens, Thermosphaera aggregans or Stetteria hydrogenophila Nitrosocaldus yellowstonii, proliferate below 77 ° C and Thermoproteus neutrophilus, Vulcanisaeta distributa, Thermofilum pendens, Aeropyruni pernix, Desulfurococcus mobilis and Ignisphaera aggregans, in sources with temperatures higher than 80 ° C.
In acidic environments, archaea of the genera are found: Sulfolobus, Sulfurococcus, Metallosphaera, Acidianus, Sulfurisphaera, Picrophilus, Thermoplasma, Thennocladium Y Galdivirga.
Among the eukaryotes from neutral and alkaline sources, we can cite Thermomyces lanuginosus, Scytalidium thermophilum, Echinamoeba thermarum, Marinamoeba thermophilia Y Oramoeba funiarolia.
In acidic sources you can find the genera: Pinnularia, Cyanidioschyzon, Cyanidium or Galdieria.
With temperatures ranging from 2 ° C to over 400 ° C, pressures in excess of several thousand pounds per square inch (psi), and high concentrations of toxic hydrogen sulfide (pH of 2.8), deep-sea hydrothermal vents are possibly the most extreme environments on our planet.
In this ecosystem, microbes serve as the bottom link in the food chain, deriving their energy from geothermal heat and chemicals found deep within the Earth's interior..
The fauna associated with these sources or vents is very varied, and the relationships between the different taxa are not yet fully understood..
Among the species that have been isolated are both bacteria and archaea. For example, archaea of the genus have been isolated Methanococcus, Methanopyus and thermophilic anaerobic bacteria of the genus Caminibacter.
Bacteria thrive in biofilms on which multiple organisms such as amphipods, copepods, snails, crab shrimp, tubeworms, fish, and octopus feed..
A common panorama is constituted by mussel accumulations, Bathymodiolus thermophilus, over 10 cm in length, crowding into cracks in the basaltic lava. These are usually accompanied by numerous galateid crabs (Munidopsis subsquamosa).
One of the most unusual organisms found is the tubeworm Riftia pachyptila, which can be grouped in large quantities and reach sizes close to 2 meters.
These tube worms do not have a mouth, stomach, or anus (that is, they do not have a digestive system); they are a completely closed bag, without any opening to the external environment.
The bright red color of the pen at the tip is due to the presence of extracellular hemoglobin. Hydrogen sulfide is transported through the cell membrane associated with the filaments of this plume, and through extracellular hemoglobin reaches a specialized "tissue" called a trophosome, composed entirely of symbiotic chemosynthetic bacteria..
It can be said that these worms have an internal “garden” of bacteria that feed on hydrogen sulfide and provide the “food” for the worm, an extraordinary adaptation.
Hot deserts cover 14-20% of the Earth's surface, roughly 19-25 million km.
The hottest deserts, such as the Sahara of North Africa and the deserts of the southwestern US, Mexico and Australia, are found throughout the tropics in both the northern and southern hemispheres (between approximately 10 ° and 30- 40 ° latitude).
A defining characteristic of a hot desert is aridity. According to the Koppen-Geiger climate classification, deserts are regions with an annual rainfall of less than 250 mm.
However, annual precipitation can be a misleading index, as water loss is a decisive factor in the water budget..
Thus, the United Nations Environmental Program definition of desert is an annual moisture deficit under normal climatic conditions, where potential evapotranspiration (PET) is five times greater than actual precipitation (P)..
High PET is prevalent in hot deserts because, due to lack of cloud cover, solar radiation approaches the maximum in arid regions.
Deserts can be divided into two types according to their level of aridity:
Deserts are distinguished from arid semi-arid lands (P / PET 0.2-0.5) and from dry sub-humid lands (0.5-0.65).
Deserts have other important characteristics, such as their strong temperature variations and the high salinity of their soils..
On the other hand, a desert is usually associated with dunes and sand, however, this image only corresponds to 15-20% of all of them; rocky and mountainous landscapes are the most frequent desert environments.
The inhabitants of the deserts, which are thermophiles, have a series of adaptations to face the adversities that arise from the lack of rain, high temperatures, winds, salinity, among others.
Xerophytic plants have developed strategies to avoid perspiration and store as much water as possible. The succulence or thickening of stems and leaves is one of the most used strategies.
It is evident in the Cactaceae family, where the leaves have also been modified in the form of spines, both to avoid evapotranspiration and to repel herbivores..
The gender Lithops or stone plants, native to the Namibian desert, also develop succulence, but in this case the plant grows flush with the ground, camouflaging with the surrounding stones.
On the other hand, animals that live in these extreme habitats develop all kinds of adaptations, from physiological to ethological. For example, the so-called kangaroo rats present low-volume urination in a small number, making these animals very efficient in their water-scarce environment..
Another mechanism to reduce water loss is an increase in body temperature; for example, the body temperature of resting camels can increase in the summer from about 34 ° C to over 40 ° C.
Temperature variations are of great importance in water conservation, due to the following:
Another example is the sand rat (Psammomys obesus), which has developed a digestive mechanism that allows them to feed only on desert plants of the Chenopodiaceae family, which contain large amounts of salts in the leaves.
The ethological (behavioral) adaptations of desert animals are numerous, but perhaps the most obvious implies that the activity-rest cycle is reversed.
In this way, these animals become active at sunset (nocturnal activity) and cease to be active at dawn (daytime rest), thus their active life does not coincide with the hottest hours..
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