Acidophiles: Overview, Examples and Environments

Anne Kamiya, Danielle Reid
  • Author
    Anne Kamiya

    Anne has experience in science research and writing. She has a graduate degree in nutrition (gut microbiome & nutritional microbiology) and undergraduate degrees in microbiology (immunology & medical microbiology) and English (myth & folklore). She has also worked as an ocean & Earth science educator.

  • Instructor
    Danielle Reid

    Danielle has taught middle school science and has a doctorate degree in Environmental Health

Explore acidophiles. Learn the definition of an acidophile and understand how it adapts to its environment. Discover where acidophiles live and see examples. Updated: 02/24/2022

What are Acidophiles?

Ecosystems in nature range from moderate to extreme. Humans live in moderate areas with distinct fluctuations in temperature and humidity. Although the environments inhabited by humans can vary considerably, none of these environments are considered extreme. Examples of extreme environments are hydrothermal vents, active volcanoes, the snow-topped peaks of the highest mountains and the deepest depths of the ocean. The abyss of space is also an extreme environment. Extreme environments are places with extraordinary extremes in temperature, oxygen levels, hydration, pressure, radiation, pH, or salinity.

Extreme environments are incompatible with most life, but some organisms thrive in these seemingly inhospitable places. Living and thriving in extreme environments requires specialized adaptations. Organisms that live in extreme environments are called extremophiles. Most extremophiles are microscopic organisms and belong to the domain archaea, but many extremophile bacteria and eukaryotes also exist.

Some extremophile categories include:

  • Acidophiles: lives in very acidic environments
  • Alkaliphiles: lives in very alkaline environments
  • Barophiles: lives in very high-pressure environments
  • Halophile: lives in very high-salt environments
  • Psychrophile: lives in extremely cold environments
  • Hyperthermophiles: lives in extremely hot environments
  • Radiophiles: lives in radioactive environments

Examples of extremophile eukaryotes are fungi, brine shrimp, tardigrades (they can survive in almost any environment), and the naked mole-rat, a mammal that subsists in extremely low-oxygen environments.


The naked mole-rat is a rare mammal extremophile. These creatures live in large colonies in low oxygen environments and can adapt and survive when other mammals would quickly suffocate and die from the lack of oxygen.

The naked mole-rat is a multicellular eukaryote, a mammal and and an extremophile.


Acidophiles are a type of extremophile that thrives in strong acid environments. The root word -phile means to love or adore, so extremophile translates to a lover of extremes, while acidophile translates to a lover of acid. Most extremophiles in this category are archaea or acidophilic bacteria.

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. 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!

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Where Do Acidophiles Live?

Acidophiles live in places with extremely low pH levels (0-3), including naturally occurring solfataric fields (sulfuric volcanic fields), geysers, sulfuric acid pools, and human-created environments like acid mine drainages from coal and metal mining waste.


The Excelsior Geyser Crater in Yellowstone National Park. This geyser is an example of a place where extremophiles live.

Steam rising from the Excelsior Geyser Crater in Yellowstone National Park.


Acidic Environments

The pH scale is a chemical scale ranking how acidic or alkaline (basic) something is and ranges from 0-14, with 0 being the most acidic and 14 being the most alkaline. Because 7 is in the middle, a pH of 7 is neutral.

In the human body, blood stays within a very narrow pH range, between 7.35-7.45. Human beings are extremely sensitive to blood pH changes, and several biological processes work tirelessly to keep this narrow range in perpetual balance. If blood pH goes above or below those values, severe illness and death occur. The pH of human blood is close to neutral.

The pH scale measurement of acidity versus alkalinity is determined by how many free hydrogen ions (H+) are in something. More free hydrogen ions (H+) mean something is more acidic. The fewer hydrogen ions something has, the more free hydroxyl ions (OH-) it has, and the more alkaline (or basic) it is. Acidity begins when the pH goes below 7, and strong acids generally have a pH of 3 or less. Alkalinity begins when the pH goes above 7, and a strong base generally has a pH of 11 or more. Each number on the scale is logarithmic, which means each number represents an increase or decrease by a factor of 10 in acidity or alkalinity. So, this means that something with a pH of 1.0 is 10 times more acidic than something with a pH of 2.0 and one million times more acidic than something with a pH of 7.0.


Image of the pH scale showing lowest acidic range of 0 to highest alkaline range of 14.

A standard scale of pH showing ranges from highly acidic to highly basic.


Extremes of pH, like sulfuric acid, which frequently has a pH of 1 or less, are extremely corrosive, and exposure will cause tissue destruction and death in human beings and the majority of life forms on Earth. Acidophiles, on the other hand, thrive in sulfuric acid, which is a common environment for them.

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:

sulfur

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?

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Video Transcript

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. 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:

sulfur

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?

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Frequently Asked Questions

Which organisms are acidophiles?

Acidophiles primarily consist of bacteria and archaea. Sulfolobus acidocaldarius, Ferroplasma acidarmanus and Acidithiobacillus caldus are three examples of microscopic acidophiles.

What does "acidophilic organism" mean?

An acidophilic organism is a life form that can survive in extremely acidic environments, like geysers and sulfuric acid pools, that would be fatal to regular life forms. "Acidophilic" means "acid-loving."

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