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Actinomyces israelii.jpg
Scanning electron micrograph of Actinomyces israelii.
Scientific classification e
Domain: Bacteria
(unranked): Terrabacteria
Phylum: Actinobacteria
Goodfellow, 2012
  • Actinobacteraeota Oren et al. 2015
  • Actinobacteria Stackebrandt, Rainey & Ward-Rainey 1997
  • Actinomycetes Krasil'nikov 1949

The Actinobacteria are a phylum of Gram-positive bacteria. They can be terrestrial or aquatic.[1] They are of great economic importance to humans because agriculture and forests depend on their contributions to soil systems. In soil they help to decompose the organic matter of dead organisms so the molecules can be taken up anew by plants. While this role is also played by fungi, Actinobacteria are much smaller and likely do not occupy the same ecological niche. In this role the colonies often grow extensive mycelia, like a fungus would, and the name of an important order of the phylum, Actinomycetales (the actinomycetes), reflects that they were long believed to be fungi. Some soil actinobacteria (such as Frankia) live symbiotically with the plants whose roots pervade the soil, fixing nitrogen for the plants in exchange for access to some of the plant's saccharides. Other species, such as many members of the genus Mycobacterium, are important pathogens.

Beyond the great interest in Actinobacteria 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.[2] Actinobacteria is one of the dominant bacterial phyla and contains one of the largest of bacterial genera, Streptomyces.[3] Streptomyces and other actinobacteria are major contributors to biological buffering of soils.[4] They are also the source of many antibiotics.

Although some of the largest and most complex bacterial cells belong to the Actinobacteria, the group of marine Actinomarinales has been described as possessing the smallest free-living prokaryotic cells.[5]

Some Siberian or Antarctic Actinobacteria is said to be the oldest living organism on Earth, frozen in permafrost at around half a million years ago.[6][7] The symptoms of life were detected by CO
release from permafrost samples 640 kya or younger. [8]


Most Actinobacteria of medical or economic significance are in subclass Actinobacteridae, and belong to the order Actinomycetales. While many of these cause disease in humans, Streptomyces is notable as a source of antibiotics.

Of those Actinobacteria not in the Actinomycetales, Gardnerella is one of the most researched. Classification of Gardnerella is controversial, and MeSH catalogues it as both a Gram-positive and Gram-negative organism.[9]

Actinobacteria, especially Streptomyces spp., are recognized as the producers of many bioactive metabolites that are useful to humans in medicine, such as antibacterials,[10] antifungals,[11] antivirals, antithrombotics, immunomodifiers, antitumor drugs, and enzyme inhibitors; and in agriculture, including insecticides, herbicides, fungicides, and growth-promoting substances for plants and animals.[12][13] Actinobacteria-derived antibiotics that are important in medicine include aminoglycosides, anthracyclines, chloramphenicol, macrolide, tetracyclines, etc.

Actinobacteria have high guanine and cytosine content in their DNA.[14] The G+C content of Actinobacteria can be as high as 70%, though some may have a low G+C content.[15]

Analysis of glutamine synthetase sequence has been suggested for phylogenetic analysis of the Actinobacteria.[16]


The phylogeny is based on 16S rRNA-based LTP release 123 by 'The All-Species Living Tree' Project.[17]

Rubrobacter Suzuki et al. 1989


Gaiella occulta Albuquerque et al. 2012

Thermoleophilum Zarilla and Perry 1986





Euzebya tangerina Kurahashi et al. 2010

Nitriliruptor alkaliphilus Sorokin et al. 2009


Acidothermus cellulolyticus Mohagheghi et al. 1986


Motilibacter peucedani Lee 2012

Streptomyces Waksman and Henrici 1943 emend. Witt and Stackebrandt 1991 [incl. Kitasatospora & Streptacidiphilus]




Kineococcus Yokota et al. 1993


Angustibacter luteus Tamura et al. 2010

Micrococcineae [incl. Actinomycetaceae & Bifidobacteriaceae]


Nocardioidaceae 2

Thermobispora bispora (Henssen 1957) Wang et al. 1996



Pseudonocardiaceae [incl. Actinopolyspora]




Actinocatenispora Thawai et al. 2006 emend. Seo and Lee 2009

Phytomonospora endophytica Li et al. 2011



The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[18] and National Center for Biotechnology Information (NCBI).[19]

♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LSPN)

See also[edit]


  1. ^ Servin JA, Herbold CW, Skophammer RG, Lake JA (January 2008). "Evidence excluding the root of the tree of life from the actinobacteria". Mol. Biol. Evol. 25 (1): 1–4. doi:10.1093/molbev/msm249. PMID 18003601.
  2. ^ Ghai R, Rodriguez-Valera F, McMahon KD, et al. (2011). Lopez-Garcia P (ed.). "Metagenomics of the water column in the pristine upper course of the Amazon river". PLOS ONE. 6 (8): e23785. Bibcode:2011PLoSO...623785G. doi:10.1371/journal.pone.0023785. PMC 3158796. PMID 21915244.
  3. ^ C.Michael Hogan.. 2010. Bacteria. Encyclopedia of Earth. eds. Sidney Draggan and C.J.Cleveland, National Council for Science and the Environment, Washington DC Archived 2011-05-11 at the Wayback Machine
  4. ^ Ningthoujam, Debananda S.; Sanasam, Suchitra; Tamreihao, K; Nimaichand, Salam (November 2009). "Antagonistic activities of local actinomycete isolates against rice fungal pathogens". African Journal of Microbiology Research. 3 (11): 737–742.
  5. ^ Ghai R, Mizuno CM, Picazo A, Camacho A, Rodriguez-Valera F (2013). "Metagenomics uncovers a new group of low GC and ultra-small marine Actinobacteria". Scientific Reports. 3: 2471. Bibcode:2013NatSR...3E2471G. doi:10.1038/srep02471. PMC 3747508. PMID 23959135.
  6. ^ Sussman: Oldest Plants, The Guardian, 2 May 2010
  7. ^ "It's Okay to be Smart • the oldest living thing in the world: These". Archived from the original on 2018-07-13. Retrieved 2018-07-13.
  8. ^ Johnson, S. S.; Hebsgaard, M. B.; Christensen, T. R.; Mastepanov, M.; Nielsen, R.; Munch, K.; Brand, T.; Gilbert, M. T. P.; Zuber, M. T.; Bunce, M.; Ronn, R.; Gilichinsky, D.; Froese, D.; Willerslev, E. (2007). "Ancient bacteria show evidence of DNA repair". Proceedings of the National Academy of Sciences. 104 (36): 14401–14405. Bibcode:2007PNAS..10414401J. doi:10.1073/pnas.0706787104. PMC 1958816. PMID 17728401.
  9. ^ Gardnerella at the US National Library of Medicine Medical Subject Headings (MeSH)
  10. ^ Mahajan, GB (2012). "Antibacterial agents from actinomycetes - a review". Frontiers in Bioscience. 4: 240–53. doi:10.2741/e373.
  11. ^ Gupte, M.; Kulkarni, P.; Ganguli, B.N. (2002). "Antifungal Antibiotics". Appl. Microbiol. Biotechnol. 58 (1): 46–57. doi:10.1007/s002530100822. PMID 11831475. S2CID 8015426.
  12. ^ Bressan, W (2003). "Biological control of maize seed pathogenic fungi by use of actinomycetes". Biocontrol. 48 (2): 233–240. doi:10.1023/a:1022673226324. S2CID 29320215.
  13. ^ Atta, M.A (2009). "Antimycin-A Antibiotic Biosynthesis Produced by Streptomyces Sp. AZ-AR-262: Taxonomy, Fermentation, Purification and Biological Activities". Austral. J. Basic and Appl. Sci. 3: 126–135.
  14. ^ Ventura, M.; Canchaya, C.; Tauch, A.; Chandra, G.; Fitzgerald, G. F.; Chater, K. F.; van Sinderen, D. (5 September 2007). "Genomics of Actinobacteria: Tracing the Evolutionary History of an Ancient Phylum". Microbiology and Molecular Biology Reviews. 71 (3): 495–548. doi:10.1128/MMBR.00005-07. hdl:11381/1721088. PMC 2168647. PMID 17804669.
  15. ^ Ghai R, McMahon KD, Rodriguez-Valera F (2012). "Breaking a paradigm:cosmopolitan and abundant freshwater actinobacteria are low GC". Environmental Microbiology Reports. 4 (1): 29–35. doi:10.1111/j.1758-2229.2011.00274.x. PMID 23757226.
  16. ^ Hayward D, van Helden PD, Wiid IJ (2009). "Glutamine synthetase sequence evolution in the mycobacteria and their use as molecular markers for Actinobacteria speciation". BMC Evol. Biol. 9: 48. doi:10.1186/1471-2148-9-48. PMC 2667176. PMID 19245690.
  17. ^ 'The All-Species Living Tree' Project."16S rRNA-based LTP release 123 (full tree)" (PDF). Silva Comprehensive Ribosomal RNA Database. Retrieved 2016-03-20.
  18. ^ J.P. Euzéby. "Actinobacteria". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved 2016-03-20.
  19. ^ Sayers; et al. "Actinobacteria". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2016-03-20.

Further reading[edit]

External links[edit]