The Extremophiles They are organisms that live in extreme environments, that is, those that are far from the conditions in which most of the organisms known to humans live.
The terms "extreme" and "extremophile" are relatively anthropocentric, because humans evaluate habitats and their inhabitants, based on what would be considered extreme for our own existence.
Due to the aforementioned, what characterizes an extreme environment is that it presents intolerable conditions for human beings regarding its temperature, humidity, salinity, light, pH, oxygen availability, toxicity levels, among others..
From a non-anthropocentric perspective, human beings could be extremophiles, depending on the organism that evaluated them. For example, from the point of view of a strict anaerobic organism, for which oxygen is toxic, aerobic beings (like humans) would be extremophiles. For the human being, on the contrary, anaerobic organisms, are extremophiles.
Article index
Currently we define as “extreme” numerous environments inside and outside the planet Earth and we constantly discover organisms capable, not only of surviving, but also of widely thriving in many of them.
In 1974, R. D. Macelroy proposed the term "Extremophiles" to define these organisms that exhibit optimal growth and development under extreme conditions, as opposed to mesophilic organisms, which grow in environments with intermediate conditions..
According to Macelroy:
"Extremophile is a descriptive for organisms capable of populating environments hostile to mesophiles, or organisms that only grow in intermediate environments".
There are two basic degrees of extremism in organisms: those that can tolerate an extreme environmental condition and becoming dominant over others; and those that grow and develop optimally under extreme conditions.
The denomination of an environment as "extreme" responds to an anthropogenic construction, based on the consideration of the distant extremes of the baseline of a certain environmental condition (temperature, salinity, radiation, among others), which allows human survival.
However, this name must be based on certain characteristics of an environment, from the perspective of the organism that inhabits it (rather than the human perspective)..
These characteristics include: biomass, productivity, biodiversity (number of species and representation of higher taxa), diversity of processes in ecosystems and specific adaptations to the environment of the organism in question..
The sum total of all these characteristics denotes the extreme condition of an environment. For example, an extreme environment is one that generally presents:
The term Extremophilic frequently refers to prokaryotes, such as bacteria, and is sometimes used interchangeably with Archaea..
However, there is a wide variety of Extremophilic organisms and our knowledge of phylogenetic diversity in extreme habitats is increasing almost daily..
We know for example that all hyperthermophiles (heat lovers) are members of Archaea and Bacteria. Eukaryotes are common among psychrophiles (lovers of cold), acidophiles (lovers of low pH), alkalophiles (lovers of high pH), xerophiles (lovers of dry environments) and halophiles (lovers of salt).
Multicellular organisms, such as invertebrate and vertebrate animals, can also be extremophiles.
For example, some psychrophiles include a small number of frogs, turtles and a snake, which during the winter avoid intracellular freezing in their tissues, accumulating osmolytes in the cell cytoplasm and allowing the freezing of only extracellular water (external to the cells)..
Another example is the case of the Antarctic nematode Panagrolaimus davidi, which can survive intracellular freezing (freezing of water within its cells), being able to grow and reproduce after thawing.
Also the fish of the Channichthyidae family, inhabitants of the cold waters of Antarctica and the south of the American continent, use antifreeze proteins to protect their cells against their complete freezing..
Poly-Extremophiles are organisms that can survive more than one extreme condition at the same time, thus being common in all extreme environments..
For example, desert plants that survive extreme heat, limited water availability, and often high salinity.
Another example would be the animals that inhabit the seabed, which are capable of withstanding very high pressures, such as lack of light and lack of nutrients, among others..
Environmental extremes are traditionally defined based on abiotic factors, such as:
Extremophiles are similarly described on the basis of the extreme conditions they endure..
The most important extreme environments that we can recognize according to their abiotic conditions are:
Extremely cold environments are those that frequently persist or fall for periods (short or long) of temperatures below 5 ° C. These include the Earth's poles, mountainous regions, and some deep ocean habitats. Even some very hot deserts during the day have very low temperatures at night..
There are other organisms that live in the cryosphere (where water is in a solid state). For example, organisms that live in ice matrices, permafrost, under permanent or periodic snow covers, must tolerate multiple extremes, including cold, desiccation, and high levels of radiation..
Extremely hot habitats are those that remain or periodically reach temperatures above 40 ° C. For example, hot deserts, geothermal sites, and deep-sea hydrothermal vents.
They are often associated with extreme high temperatures, environments where available water is very limited (persistently or for regular periods of time), such as hot and cold deserts, and some endolithic habitats (located within rocks).
Other environments are subject to high hydrostatic pressure, such as the benthic zones of oceans and deep lakes. At these depths, its inhabitants must withstand pressures greater than 1000 atmospheres.
Alternatively, there are hypobaric extremes (of low atmospheric pressure), in mountains and in other elevated regions of the world.
In general, extremely acidic environments are those that maintain or regularly reach values below pH 5.
Low pH, in particular, increases the “extreme” condition of an environment, since it increases the solubility of the metals present and the organisms that live in them must be adapted to face multiple abiotic extremes..
Conversely, extremely alkaline environments are those that remain or regularly register pH values above 9.
Examples of extreme pH environments include lakes, groundwater, and highly acidic or alkaline soils.
Hypersaline environments are defined as those with salt concentrations greater than those of seawater, which has 35 parts per thousand. These environments include hypersaline and saline lakes.
With "saline" we do not refer only to salinity due to sodium chloride, as there may be saline environments where the predominant salt is something else..
Habitats with limited free oxygen (hypoxic) or no oxygen present (anoxic), either persistently or at regular intervals, are also considered extreme. For example, environments with these characteristics would be the anoxic basins in oceans and lakes, and the deeper sediment strata..
Ultraviolet (UV) or infrared (IR) radiation can also impose extreme conditions on organisms. Extreme radiation environments are those exposed to abnormally high radiation or radiation outside the normal range. For example, polar and high altitude environments (terrestrial and aquatic).
Some species have elusive mechanisms of high UV or IR radiation. For example, the Antarctic seaweed Phaeocystis pouchetii produces water-soluble “sunscreens”, which strongly absorb UV-B wavelengths (280-320nm) and protect your cells from extremely high levels of UV-B in the upper 10 m of the water column (after sea ice break).
Other organisms are very tolerant of ionizing radiation. For example, the bacteria Deinococcus radiodurans can preserve your genetic integrity by compensating for extensive DNA damage after exposure to ionizing radiation.
This bacterium uses intercellular mechanisms to limit degradation and restrict the diffusion of DNA fragments. In addition, it has highly efficient DNA repair proteins.
Even in apparently low or no radiation environments, Extremophilic organisms are adapted to respond to changes in radiation levels..
For example, Astyanax hubbsi, a Mexican blind cave-dwelling fish does not have superficially perceptible ocular structures, yet it can distinguish small differences in ambient light. Use extraocular photoreceptors to detect and respond to moving visual stimuli.
We currently live in an environment where extreme environmental conditions are imposed, artificially generated as an effect of human activities..
So-called anthropogenic impact environments are extremely varied, global in scope, and can no longer be ignored when defining certain extreme environments.
For example, environments affected by pollution (atmospheric, water and soil) -such as climate change and acid rain-, extraction of natural resources, physical disturbance and overexploitation.
In addition to the extreme environments mentioned above, terrestrial ecologists have always been aware of the special nature of transition zones between two or more diverse communities or environments, such as the tree line in mountains or the boundary between forests and grasslands. . These are called tension belts or ecotones..
Ecotones also exist in the marine environment, for example, the transition between ice and water represented by the edge of the sea ice. These transition zones typically exhibit greater species diversity and biomass density than the flanking communities, in large part because the organisms that live in them can take advantage of the resources of the adjacent environments, which can give them an advantage..
However, ecotones are continuously changing and dynamic regions, often showing a wider range of variation in abiotic and biotic conditions over an annual period than adjacent environments..
This could reasonably be considered “extreme”, because it requires organisms to continuously adapt their behavior, phenology (seasonal time) and interactions with other species..
Species that live on both sides of the ecotone are often more tolerant of dynamics, while species whose range is limited to one side experience the other side as extreme..
In general, these transition zones are also often the first to be affected by changes in climate and / or disturbances, both natural and anthropogenic..
Not only are environments dynamic, and may or may not be extreme, but organisms are also dynamic and have life cycles with different stages, adapted to particular environmental conditions..
It may happen that the environment that supports one of the stages of the life cycle of an organism is extreme for another of the stages.
For example, the coconut (Cocos nucifera), presents a seed adapted for transport by sea, but the mature tree grows on land.
In vascular spore-bearing plants, such as ferns and different types of mosses, the gametophyte may be devoid of photosynthetic pigments, have no roots, and depend on environmental humidity..
While sporophytes have rhizomes, roots and shoots that withstand hot and dry conditions in full sunlight. The difference between sporophytes and gametophytes is in the same order as the differences between taxa.
A very close example is constituted by the juvenile stages of many species, which are generally intolerant to the environment that usually surrounds the adult, so they usually require protection and care during the period during which they acquire the skills and strengths that allow them. allow dealing with these environments.
Yet No Comments