Have of adaptation, including: An acidophile’s release

Have you ever heard of a microbial organism called an acidophile? Continue this lesson to learn about this fascinating microorganisms, their relationship to acidity, and their importance to our ecosystem.

Definition of Acidophiles

On Earth, we have the opportunity to explore places that are naturally cold and, of course, very hot. We know of areas where rain is constant and humidity makes us sweat. But, can you imagine visiting a place where plants do not thrive and most living organisms can’t survive due to high acidity levels? This environment surely exists, and it just so happens our friend the acidophile resides there.Acidophiles are microorganisms that thrive in acidic environments where the pH level is less than 3. Think of an acidophile as a microbe that is an acid lover.

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These organisms are tough guys who feel right at home in nasty, typically unlivable places. In fact, these organisms belong to a larger family called extremophiles, which is a group that thrives in extreme environments normally inhospitable to other organisms. Acidophiles belong to all three domains: Eukaryote, Bacteria, and Archaea. Examples of acidophiles include Thiobacillus acidophilus (a type of bacteria), Vorticella (a type of eukaryote), and Crenarchaeota (a type of archaea).

Scientists have identified several areas, natural and manmade, that are acidic enough for acidophiles to thrive in. An example of a natural acidic environment are certain hot springs (containing sulfurous gas) at Yellowstone National Park. Other environments include volcanic sites, debris that remains from coal mining activities, and our own stomachs!

How Acidophiles Survive

Of course, you may be wondering how a microorganism can survive in such extreme conditions.

The versatile nature of an acidophile can answer that question: acidophiles have developed a way to adapt to these surroundings. If we dust off our biology book, we will see that inside the cell of an organism is a cytoplasm, a solution that surrounds the nucleus of a cell. Scientists first believed that the cytoplasm inside an acidophile must be acidic in order to thrive in such conditions. Later research findings revealed that this was false. The cytoplasm of an acidophile was comparable to a normal cell, as it had a neutral pH (i.e., a pH of 7) rather than an acidic one.

Scientists also discovered other methods of adaptation, including:

  • An acidophile’s release of protective coatings on the outside of its cell to protect it from damage to the acidic environment
  • Efficient cellular mechanisms within the cytoplasm that combat or buffer extreme changes in pH (within the cell)

Each of these characteristics, along with others, support an acidophile’s ability to adapt to an extreme environment and thrive.

Acidic Environments

Although it is important to understand what an acidophile is and where it lives, it is equally important to understand how these acidic environments are formed. Naturally formed and created from human activities, such environments have a common factor: the presence of sulfur.

You can see the equation representing this process:


Naturally acidic environments are created when inorganic sulfur rises to the surface and becomes oxidized to form sulfuric acid. Oxidization is the ability to chemically combine a compound (or element) with oxygen. When sulfur rises to the surface, it interacts with oxygen in the air and water to produce sulfuric acid.Sulfuric acid is a very strong acid. Strong acids are known to completely dissociate (break apart) in solution. The standard pH level of sulfuric acid is 2.

1. However, acidic environments can have pH levels less than 2.1. In fact, scientists have found environments so extreme that the pH levels were recorded as 0. Now that is what we call acidic! But, what is the connection between variability in pH for an acidic environment and the presence of sulfuric acid?As a strong acid, sulfuric acid dissociates into hydrogen ions in solution. The concentration of hydrogen ions directly affects pH. Thus, if a large volume of sulfur rises to the surface and is oxidized the concentration of sulfuric acid will be high.

The greater the number of hydrogen ions (from the dissociation of sulfuric acid) present in this environment, the lower the pH level will be. This explains why some acidic environments may have a pH level of 3, and others have a pH of 1. Just remember the pH level is dependent on:

  1. The concentration of sulfur oxidized to sulfuric acid
  2. The number of hydrogen ions in solution

Besides natural processes, sulfur can also be released from sulfur containing minerals during a manmade event called acid mine drainage. This release of sulfur undergoes the same chemical process of oxidation to form sulfuric acid.

Acidophile Example

As we discussed, some of Yellowstone National Park’s hot springs are acidic enough for acidophiles to survive.

Perhaps the most well-known acidophile, Thermus aquaticus, lives in these springs. When it was discovered here in the 1960s, its presence was a surprise–researchers didn’t believe that any organism could survive in the springs’ temperatures, which reached beyond 130 degrees Fahrenheit. However, Thermus aquaticus thrived here due to a special variant enzyme that allowed it to function in high temperatures. That same enzyme is now used in the polymerase chain reaction method that allows us to conduct DNA fingerprinting.

Lesson Summary

Acidophiles, whose name literally means ‘acid lover,’ are microorganisms that thrive in acidic environments where the pH level is less than 3. They are also classified as extremophiles, which is a group that thrives in extreme environments normally inhospitable to other organisms.

Acidophiles are part of the Eukaryote, Archaea, and Bacteria domains. Biologically, these microorganisms thrive due to various cellular adaptations (though not with their cytoplasm, a solution that surrounds the nucleus of a cell, as scientists originally believed).Examples of places where these organisms thrive range from natural sources such as hot springs and volcanic sites to manmade sources such as acid mine drainage activity. These acidic environments are formed when sulfur oxidizes (when a compound chemically combines with oxygen) to produce sulfuric acid.

As a strong acid which are known to completely dissociate (break apart) in solution, the concentration of hydrogen ions in solution directly influences the pH level of the acidic environment.


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