Acidophiles or acidophilic organisms are those that thrive under highly acidic conditions (usually at pH 5.0 or below). These organisms can be found in different branches of the

tree of life The tree of life is a fundamental archetype in many of the world's mythological, religious, and philosophical traditions. It is closely related to the concept of the sacred tree.Giovino, Mariana (2007). ''The Assyrian Sacred Tree: A History ...

, including

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

,Becker, A.
Types of Bacteria Living in Acidic pH"
Retrieved 10 May 2017. and

Eukarya Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

Examples

A list of these organisms includes:

Archaea

Sulfolobales In taxonomy, the Sulfolobales are an order of the Thermoprotei. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) ...

, an order in the

Thermoproteota The Thermoproteota (also known as crenarchaea) are archaea that have been classified as a phylum of the Archaea domain. Initially, the Thermoproteota were thought to be sulfur-dependent extremophiles but recent studies have identified characteris ...

branch of

Thermoplasmatales In alpha taxonomy, taxonomy, the Thermoplasmatales are an order (biology), order of the Thermoplasmata. All are acidophiles, growing optimally at pH below 2. ''Picrophilus'' is currently the most acidophile, acidophilic of all known organisms, b ...

, an order in the

Euryarchaeota Euryarchaeota (from Ancient Greek ''εὐρύς'' eurús, "broad, wide") is a phylum of archaea. Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines, halobacteria, which survive extre ...

branch of Archaea :* ARMAN, in the Euryarchaeota branch of Archaea :* ''

Acidianus In taxonomy, ''Acidianus'' is a genus of the Sulfolobaceae.See the NCBIbr>webpage on Acidianus Data extracted from the See also * List of bacterial genera named after mythological figures Several bacterial species are named after Greek or Ro ...

brierleyi, A. infernus'', facultatively anaerobic thermoacidophilic archaebacteria :* '' Halarchaeum acidiphilum'', acidophilic member of the Halobacteriacaeae :* ''

Metallosphaera In taxonomy, ''Metallosphaera'' is a genus of the Sulfolobaceae.See the NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of He ...

sedula'', thermoacidophilic

Bacteria

Acidobacteriota Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture. Description Members of this phylum are physiologically diverse, and can be ...

, a phylum of

Acidithiobacillales The Acidithiobacillales are an order of bacteria within the class ''Acidithiobacillia'' and comprises the genera ''Acidithiobacillus'' and ''Thermithiobacillus''. Originally, both were included in the genus ''Thiobacillus'', but they are not rela ...

, an order of

Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. The ...

e.g. ''A. ferrooxidans, A. thiooxidans'' :*''

Thiobacillus ''Thiobacillus'' is a genus of Gram-negative Betaproteobacteria. ''Thiobacillus thioparus'' is the type species of the genus, and the type strain thereof is the StarkeyT strain, isolated by Robert Starkey in the 1930s from a field at Rutgers Un ...

prosperus, T. acidophilus, T. organovorus, T. cuprinus'' :*''

Acetobacter ''Acetobacter'' is a genus of acetic acid bacteria. Acetic acid bacteria are characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. Of these, the genus ''Acetobacter'' is distinguished by the ability to oxidize ...

aceti'', a bacterium that produces

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

(vinegar) from the oxidation of ethanol. :*''

Alicyclobacillus ''Alicyclobacillus'' is a genus of Gram-variable, rod-shaped, spore-forming bacteria. The bacteria are able to grow in acidic conditions, while the spores are able to survive typical pasteurization procedures. Overview ''Alicyclobacilli'' ar ...

'', a genus of bacteria that can contaminate fruit juices.

Eukarya

:* ''

Mucor racemosus ''Mucor racemosus'' is a rapidly growing, weedy mould belonging to the division Mucoromycota. It is one of the earliest fungi to be grown in pure culture and was first isolated in 1886. It has a worldwide distribution and colonizes many habitats ...

'' :* ''Urotricha'' :* ''Dunaliella acidophila'' :* Members of the algal class

Cyanidiophyceae Cyanidiophyceae is a class of unicellular red algae within subdivision Cyanidiophytina, and contain a single plastid, one to three mitochondria, a nucleus, a vacuole and floridean starch. Most are extremophiles inhabiting acid hot springs. The ...

, including ''

Cyanidioschyzon merolae ''Cyanidioschyzon merolae'' is a small (2μm), club-shaped, unicellular haploid red alga adapted to high sulfur acidic hot spring environments (pH 1.5, 45 °C). The cellular architecture of ''C. merolae'' is extremely simple, containing only ...

Mechanisms of adaptation to acidic environments

Most acidophile organisms have evolved extremely efficient mechanisms to pump protons out of the

intracellular space Intracellular space is the interior space of the plasma membrane. It contains about two-thirds of TBW. Cellular rupture may occur if the intracellular space becomes dehydrated, or if the opposite happens, where it becomes too bloated. Thus it i ...

in order to keep the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

at or near neutral pH. Therefore, intracellular proteins do not need to develop acid stability through evolution. However, other acidophiles, such as ''

aceti'', have an acidified cytoplasm which forces nearly all proteins in the genome to evolve acid stability. For this reason, ''Acetobacter aceti'' has become a valuable resource for understanding the mechanisms by which proteins can attain acid stability. Studies of proteins adapted to low pH have revealed a few general mechanisms by which proteins can achieve acid stability. In most acid stable proteins (such as pepsin and the soxF

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

from ''Sulfolobus acidocaldarius''), there is an overabundance of acidic residues which minimizes low pH destabilization induced by a buildup of positive charge. Other mechanisms include minimization of solvent accessibility of acidic residues or binding of metal cofactors. In a specialized case of acid stability, the NAPase protein from ''Nocardiopsis alba'' was shown to have relocated acid-sensitive salt bridges away from regions that play an important role in the unfolding process. In this case of kinetic acid stability, protein longevity is accomplished across a wide range of pH, both acidic and basic.

Examples

Archaea

Bacteria

Eukarya

Mechanisms of adaptation to acidic environments

See also

References

Further reading