Actinobacteria
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The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all
gram-positive bacteria In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
. They can be terrestrial or aquatic. They are of great economic importance to humans because
agriculture Agriculture or farming is the practice of cultivating Plant, plants and livestock. Agriculture was the key development in the rise of Sedentism, sedentary human civilization, whereby farming of Domestication, domesticated species created food ...
and
forest A forest is an area of land dominated by tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, usually supporting branches and leaves. In some usages, the definition of a tree may ...
s depend on their contributions to
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organism In biology, an organism () is any life, living system that functions as an individual entity. All organi ...
systems. In soil they help to
decompose Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...
the
organic matter Organic matter, organic material, or natural organic matter refers to the large source of Carbon compounds, carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic comp ...
of dead organisms so the molecules can be taken up anew by
plant Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...
s. While this role is also played by
fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
, ''Actinomycetota'' are much smaller and likely do not occupy the same
ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources a ...
. In this role the
colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the ''metropole, metropolit ...
often grow extensive
mycelia Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...
, like a fungus would, and the name of an important order of the phylum, ''
Actinomycetales The Actinomycetales is an order of Actinomycetota The ''Actinomycetota'' (synonym ''Actinobacteria'') are a phylum of mostly Gram-positive bacteria. They can be terrestrial animal, terrestrial or aquatic animal, aquatic. They are of great eco ...
'' (the actinomycetes), reflects that they were long believed to be fungi. Some soil actinomycetota (such as ''
Frankia ''Frankia'' is a genus of Nitrogen fixation, nitrogen-fixing Filamentation, bacteria that live in symbiosis with actinorhizal plants, similar to the ''Rhizobium'' bacteria found in the root nodules of legumes in the family Fabaceae. ''Frankia'' ...
'') live symbiotically with the plants whose
root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often b ...
s pervade the soil,
fixing nitrogen Nitrogen fixation is a chemical process by which molecular nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of pnictogen, group 15 of the perio ...
for the plants in exchange for access to some of the plant's
saccharide In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or may ...
s. Other species, such as many members of the genus ''
Mycobacterium ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (''Mycobacterium tuberculos ...
'', are important
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ ...
s. Beyond the great interest in ''Actinomycetota'' for their soil role, much is yet to be learned about them. Although currently understood primarily as soil bacteria, they might be more abundant in fresh waters. ''Actinomycetota'' is one of the dominant bacterial phyla and contains one of the largest of bacterial genera, ''
Streptomyces ''Streptomyces'' is the largest genus of Actinomycetota and the type genus of the family Streptomycetaceae. Over 500 species of ''Streptomyces'' bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positi ...
''. ''Streptomyces'' and other actinomycetota are major contributors to biological buffering of soils. They are also the source of many
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
s. The ''Actinomycetota'' genus ''
Bifidobacterium ''Bifidobacterium'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of bi ...
'' is the most common bacteria in the
microbiome A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably well ...
of human infants. Although adults have fewer bifidobacteria, intestinal bifidobacteria help maintain the mucosal barrier and reduce
lipopolysaccharide Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the Bacterial ...
in the intestine. Although some of the largest and most complex bacterial cells belong to the ''Actinomycetota'', the group of marine Actinomarinales has been described as possessing the smallest free-living
prokaryotic A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek language, Greek wikt:πρό#Ancient Greek, πρό (, 'before') a ...
cells. Some
Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive region, geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a ...
n or
Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar regions of Earth, polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kergu ...
''Actinomycetota'' is said to be the oldest living organism on Earth, frozen in permafrost at around half a million years ago. The symptoms of life were detected by release from permafrost samples 640 kya or younger.


General

Most ''Actinomycetota'' of medical or economic significance are in class
Actinomycetia The Actinomycetia are a class of bacteria. Taxonomy The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). * Acidothermales Sen et ...
, and belong to the order
Actinomycetales The Actinomycetales is an order of Actinomycetota The ''Actinomycetota'' (synonym ''Actinobacteria'') are a phylum of mostly Gram-positive bacteria. They can be terrestrial animal, terrestrial or aquatic animal, aquatic. They are of great eco ...
. While many of these cause disease in humans, ''Streptomyces'' is notable as a source of
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
. Of those ''Actinomycetota'' not in the Actinomycetales, '' Gardnerella'' is one of the most researched. Classification of ''Gardnerella'' is controversial, and
MeSH A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a spider web, web or a Net (textile), net in that it has many attached or woven strands. Types * A plastic mesh may ...
catalogues it as both a Gram-positive and
Gram-negative Gram-negative bacteria are bacteria that do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidogly ...
organism. ''Actinomycetota'', especially ''Streptomyces'' spp., are recognized as the producers of many bioactive metabolites that are useful to humans in medicine, such as antibacterials, antifungals, antivirals, antithrombotics, immunomodifiers, antitumor drugs, and enzyme inhibitors; and in agriculture, including insecticides, herbicides, fungicides, and growth-promoting substances for plants and animals. ''Actinomycetota''-derived antibiotics that are important in medicine include aminoglycosides, anthracyclines, chloramphenicol, macrolide, tetracyclines, etc. ''Actinomycetota'' have high guanine and cytosine content in their DNA. The G+C content of ''Actinomycetota'' can be as high as 70%, though some may have a low G+C content. Analysis of
glutamine synthetase Glutamine synthetase (GS) () is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine: Glutamate + Adenosine triphosphate, ATP + NH3 → Glutamine + Ad ...
sequence has been suggested for phylogenetic analysis of the ''Actinomycetota''.


Phylogeny


Taxonomy

The currently accepted taxonomy is based on the
List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the naming Naming is assigning a name to something. Naming may refer to: * Naming (parliamentary procedure), a procedure in cert ...
(LPSN) and
National Center for Biotechnology Information 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 (NIH). It is approved and funded by the government of the United States. The ...
(NCBI). * Class ?" Syntrophaliphaticia" corrig. Liu et al. 2020 * Class " Aquicultoria" Jiao et al. 2021 * Class " Geothermincolia" Jiao et al. 2021 * Class " Humimicrobiia" Jiao et al. 2021 * Class Acidimicrobiia Norris 2013 * Class
Actinomycetia The Actinomycetia are a class of bacteria. Taxonomy The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). * Acidothermales Sen et ...
(Stackebrandt et al. 1997) Salam et al. 2020 ( Nitriliruptoria Ludwig et al. 2013) ** Subclass Actinobacteridae Stackebrandt, Rainey & Ward-Rainey 1997 ** Subclass Nitriliruptoridae Kurahashi et al. 2010 * Class Coriobacteriia König 2013 * Class Rubrobacteria Suzuki 2013 * Class Thermoleophilia Suzuki and Whitman 2013


See also

*
List of bacteria genera This article lists the genus, genera of the bacteria. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). However many taxonomic nam ...
*
List of bacterial orders This article lists the order (biology), orders of the Bacteria. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) and the phylogen ...
* List of bacterial vaginosis microbiota


References


Further reading

* * *


External links


Actinomycetes genome database
{{Taxonbar, from1=Q130914, from2=Q62573436 Gram-positive bacteria Bacteria phyla Bacterial vaginosis