TheActinomycetota (orActinobacteria) are a diverse phylum ofGram-positive bacteria with highGC content.[4] They can beterrestrial oraquatic.[5] They are of great importance to landflora because of their contributions tosoil systems. In soil they help todecompose theorganic matter of dead organisms so the molecules can be taken up anew byplants. While this role is also played byfungi, Actinomycetota are much smaller and likely do not occupy the sameecological niche. In this role thecolonies often grow extensivemycelia, as fungi do, and the name of an important order of the phylum,Actinomycetales (the actinomycetes), reflects that they were long believed to be fungi. Some soil actinomycetota (such asFrankia) livesymbiotically with the plants whoseroots pervade the soil,fixing nitrogen for the plants in exchange for access to some of the plant'ssaccharides. Other species, such as many members of the genusMycobacterium, are importantpathogens.
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.[6] Actinomycetota is one of the dominant bacterial phyla and contains one of the largest of bacterial genera,Streptomyces.[7]Streptomyces and other actinomycetota are major contributors to biologicalbuffering of soils.[8] They are also the source of manyantibiotics.[9][10]
The Actinomycetota genusBifidobacterium is the most common bacteria in themicrobiome of human infants.[11] Although adults have fewer bifidobacteria, intestinal bifidobacteria help maintain the mucosal barrier and reducelipopolysaccharide in the intestine.[12]
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-livingprokaryotic cells.[13]
SomeSiberian orAntarctic Actinomycetota are said to be the oldest living organism on Earth, frozen in permafrost at around half a million years ago.[14][15] The symptoms of life were detected by CO2 release from permafrost samples 640 kya or younger.[16]
Most Actinomycetota of medical or economic significance are in classActinomycetia, and belong to the orderActinomycetales. While many of these cause disease in humans,Streptomyces is notable as a source ofantibiotics.[10]
Of those Actinomycetota not in the Actinomycetales,Gardnerella is one of the most researched. Classification ofGardnerella is controversial, andMeSH catalogues it as both a Gram-positive andGram-negative organism.[17]
Actinomycetota, especiallyStreptomyces spp., are recognized as the producers of many bioactive metabolites that are useful to humans in medicine, such as antibacterials,[18] antifungals,[19] antivirals, antithrombotics, immunomodifiers, antitumor drugs, and enzyme inhibitors; and in agriculture, including insecticides, herbicides, fungicides, and growth-promoting substances for plants and animals.[20] Actinomycetota-derived antibiotics that are important in medicine include aminoglycosides, anthracyclines, chloramphenicol, macrolide, tetracyclines, etc.[citation needed]
Actinomycetota have highguanine and cytosine content in theirDNA.[21] The G+C content of Actinomycetota can be as high as 70%, though some may have a low G+C content.[22]
Analysis ofglutamine synthetase sequence has been suggested for phylogenetic analysis of the Actinomycetota.[23]
^Goodfellow M (2012). "Phylum XXVI.Actinobacteria phyl. nov.". In Goodfellow M, Kämpfer P, Trujillo ME, Suzuki K, Ludwig W, Whitman WB (eds.).Bergey's Manual of Systematic Bacteriology. Vol. 5 (2nd ed.). New York, NY: Springer. pp. 33–34.
^Hogan CM (2010)."Bacteria". In Draggan S, Cleveland CJ (eds.).Encyclopedia of Earth. Washington DC: National Council for Science and the Environment. Archived fromthe original on 2011-05-11.
^Ningthoujam DS, Sanasam S, Tamreihao K, Nimaichand S (November 2009). "Antagonistic activities of local actinomycete isolates against rice fungal pathogens".African Journal of Microbiology Research.3 (11):737–742.
^Bressan W (2003). "Biological control of maize seed pathogenic fungi by use of actinomycetes".Biocontrol.48 (2):233–240.doi:10.1023/a:1022673226324.S2CID29320215.
