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 Hist ...

, 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 Archaeba ...

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 am ...

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

Examples

A list of these organisms includes:

Archaea

:* Sulfolobales, 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, 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 extr ...

branch of Archaea :*

ARMAN Arman (November 17, 1928 – October 22, 2005) was a French-born American artist. Born Armand Fernandez in Nice, France, Arman was a painter who moved from using objects for the ink or paint traces they leave (''cachets'', ''allures d'objet'') to ...

, in the Euryarchaeota branch of Archaea :* ''

Acidianus In taxonomy, ''Acidianus'' 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 Health ( ...

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

e.g. ''A. ferrooxidans, A. thiooxidans'' :*'' Thiobacillus prosperus, T. acidophilus, T. organovorus, T. cuprinus'' :*'' Acetobacter 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 componen ...

(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'' are s ...

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

Eukarya

:* '' Mucor racemosus'' :* ''Urotricha'' :* ''Dunaliella acidophila'' :* Members of the algal class Cyanidiophyceae, 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 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. ...

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

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