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, 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,
[Becker, A.]
Types of Bacteria Living in Acidic pH"
Retrieved 10 May 2017. and
Eukarya.
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 branch
of
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 ...
:*
Thermoplasmatales, an order in the
Euryarchaeota 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 brierleyi,
A. infernus'', facultatively anaerobic thermoacidophilic archaebacteria
:* ''
Halarchaeum acidiphilum
In taxonomy, the Halobacteriaceae are a family of the Halobacteriales in the domain Archaea.See the NCBIbr>webpage on Halobacteriaceae Data extracted from the ''Halobacteriaceae'' represent a large part of halophilic Archaea, along with members ...
'', acidophilic member of the
Halobacteriacaeae
:* ''
Metallosphaera sedula'', thermoacidophilic
Bacteria
:*
Acidobacteriota, a phylum of
Bacteria
:*
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. The ...
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 component ...
(vinegar) from the oxidation of ethanol.
:*''
Alicyclobacillus'', a genus of bacteria that can contaminate fruit juices.
Eukarya
:* ''
Mucor racemosus''
:* ''Urotricha''
:* ''Dunaliella acidophila''
:* Members of the algal class
Cyanidiophyceae, including ''
Cyanidioschyzon merolae''
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 at or near neutral pH. Therefore, intracellular proteins do not need to develop acid stability through evolution. However, other acidophiles, such as ''
Acetobacter aceti
''Acetobacter aceti'' is a Gram-negative bacterium that moves using its peritrichous flagella. Louis Pasteur proved it to be the cause of conversion of ethanol to acetic acid in 1864. It is a benign microorganism which is present everywhere in ...
'', 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 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.
See also
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Acidophiles in acid mine drainage
*
Acidophobe
*
Neutrophile
*
Acidophile (histology)
References
Further reading
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{{DEFAULTSORT:Acidophile (Organisms)
Physiology