ACIDOPHILES: CHARACTERISTICS, EXAMPLES OF MICROORGANISMS, APPLICATIONS - BIOLOGY - 2024

Acidophilic organisms are a type of microorganism (prokaryotic or eukaryotic) capable of reproducing and living in environments whose pH values ​​are less than 3. In fact, the term acidophilus comes from the Greek and means "acid lover".

These environments can come from volcanic activities with the release of sulfurous gases or a mixture of metallic oxides from iron mines. In addition, they can be the product of the activity or metabolism of the organisms themselves, which acidify their own environment in order to survive.

The acidic waters of the Rio Tinto serve as a habitat for a great variety of acid-phile microorganisms that give it its characteristic color. By Antonio de Mijas, Spain, from Wikimedia Commons.

Organisms classified within this category also belong to the large group of Extremophilic organisms, since they grow in environments whose pH is very acidic. Where most cells are unable to survive.

Additionally, it is important to highlight that this group of organisms are of great importance from the ecological and economic point of view.

General characteristics

Competition, predation, mutualism and synergy

Most acidophilic organisms grow and live in the presence of oxygen. However, there is evidence of acidophilus that can develop both in the absence and in the presence of oxygen.

Additionally, these organisms establish different types of interactions with other organisms such as competition, predation, mutualism and synergy. An example, are the mixed cultures of acidophilus which present a higher growth and efficiency in the oxidation of sulfur minerals than the individual cultures.

Heartburn, a problem to solve

Acidophiles appear to share distinctive structural and functional characteristics that allow them to neutralize acidity. These include highly impermeable cell membranes, a high internal regulatory capacity, and unique transport systems.

Because acidophiles live in an environment where the concentration of protons is high, they have developed pump systems responsible for expelling protons to the outside. This strategy achieves that the interior of the bacteria has a pH very close to neutral.

Acidophilic organisms have developed a system of proton pumps that allow them to pump protons outward and keep intracellular pH close to neutral. By PhilMacD, from Wikimedia Commons.

However, in mines with a high content of sulfuric acid, microorganisms without a cell wall have been found, indicating that even without this protection they are subjected to high concentrations of protons.

On the other hand, due to the extreme conditions to which these types of microorganisms are subjected, they must guarantee that all their proteins are functional and not denatured.

For this, the synthesized proteins are of high molecular weight, so that there are a greater number of bonds between the amino acids that constitute them. In this way, it becomes more difficult for the breaking of the bonds to occur and greater stability is given to the protein structure.

High membrane impermeability

Once the protons enter the cytoplasm, acidophilic organisms need to implement methods that allow them to alleviate the effects of a reduced internal pH.

To help maintain pH, acidophiles have an impermeable cell membrane that limits the entry of protons into the cytoplasm. This is due to the fact that the membrane of archaea acidophiles is composed of other types of lipids than those found in bacteria and eukaryotic cell membranes.

In archaea, phospholipids have a hydrophobic (isopenoid) region and a polar region made up of the glycerol backbone and the phosphate group. In any case, the union is due to an ether bond, which generates greater resistance, especially at high temperatures.

In addition, in some cases archaea do not have bilayers, but rather the product of the union of two hydrophobic chains, they form a monolayer where the only molecule of two polar groups gives them greater resistance.

On the other hand, despite the fact that the phospholipids that make up the membranes of bacteria and eukaryotes retain the same structure (a hydrophobic and a polar region), the bonds are ester type and form a lipid bilayer.

Importance of

Acidophilic organisms are of potential importance in evolution because the low pH and metal-rich conditions in which they grow may have been similar to the undersea volcanic conditions in early earth.

Thus, acidophilic organisms could represent primordial relics from which more complex life evolved.

Additionally, because the metabolic processes could have originated on the surface of the sulfide minerals, possibly the DNA structuring of these organisms could have taken place at acidic pH.

Regulation in acidophilic organisms

The regulation of pH is essential for all organisms, for this reason acidophiles need to have an intracellular pH close to neutral.

However, acidophilic organisms are able to tolerate pH gradients of several orders of magnitude, compared to organisms that only grow at pHs close to neutral. An example is Thermoplasma acidophilum which is capable of living at pH 1.4 while maintaining its internal pH at 6.4.

The interesting thing about acidophilic organisms is that they take advantage of this pH gradient to produce energy through a proton motive force.

Examples of acidophilic microorganisms

Acidophilic organisms are predominantly distributed in bacteria and archaea and contribute to numerous biogeochemical cycles, which include the iron and sulfur cycles.

Among the first we have Ferroplasma acidarmanus, which is an archa capable of growing in environments with a pH close to zero. Other prokaryotes are Picrophilus oshimae and Picrophilus torridus, which are also thermophilic and grow in Japanese volcanic craters.

We also have some acidophilic eukaryotes such as Cyanidyum caldariuym, which is capable of living at a pH close to zero, keeping the interior of the cell at an almost neutral level.

Acontium cylatium, Cephalosporium sp. and Trichosporon cerebriae, are three eukaryotes from the Fungi Kingdom. Others equally interesting are Picrophilus oshimae and Picrophilus torridus.

Applications

Leaching

An important role of acidophilic microorganisms involves their biotechnological application, specifically in the extraction of metals from minerals, which considerably reduces the contaminants that are generated by traditional chemical methods (leaching).

This process is especially useful in copper mining, where, for example, Thobacillus sulfolobus can act as a catalyst and accelerate the rate of oxidation of the copper sulfate that forms during oxidation, helping the solubilization of the metal.

Food industry

Acidophilic organisms have enzymes of industrial interest, being a source of acid-stable enzymes with applications as lubricants.

Additionally, in the food industry the production of amylases and glucoamylases are used for the processing of starch, the bakery, the processing of fruit juices.

In addition, they are widely used in the production of proteases and cellulases that are used as animal feed components and in the manufacture of pharmaceutical products.

References

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