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Scanning electron micrograph of Actinomyces israelii.
Scientific classification
Domain: Bacteria
Phylum: Actinobacteria
Class: Actinobacteria

Actinobacteria are a group of Gram-positive bacteria with high G+C ratio.[1][2 ] They can be terrestrial or aquatic.[3]

Use of the ferric uptake regulator (fur) has been suggested for classification.[4] Analysis of glutamine synthetase has also been suggested.[5]



They include some of the most common soil life, freshwater and marine life, playing an important role in decomposition of organic materials, such as cellulose and chitin and thereby playing a vital part in organic matter turnover and carbon cycle. This replenishes the supply of nutrients in the soil and is an important part of humus formation. Other Actinobacteria inhabit plants and animals, including a few pathogens, such as Mycobacterium, Corynebacterium, Nocardia, Rhodococcus and a few species of Streptomyces.

Actinobacteria are well known as secondary metabolite producers and hence of high pharmacological and commercial interest. In 1940 Selman Waksman discovered that the soil bacteria he was studying made actinomycin, a discovery which granted him a Nobel Prize. Since then hundreds of naturally occurring antibiotics have been discovered in these terrestrial microorganisms, especially from the genus Streptomyces.

Some Actinobacteria form branching filaments, which somewhat resemble the mycelia of the unrelated fungi, among which they were originally classified under the older name Actinomycetes. Most members are aerobic, but a few, such as Actinomyces israelii, can grow under anaerobic conditions. Unlike the Firmicutes, the other main group of Gram-positive bacteria, they have DNA with a high GC-content and some Actinomycetes species produce external spores.

Some types of Actinobacteria are responsible for the peculiar odor emanating from the soil after rain, mainly in warmer climates.[6]


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

Of those Actinobacteria not in 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.[7]

Genomes of 44 different strains of Actinobacteria from different genera are either already sequenced or underway right now.


External links



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Wikispecies has information on:


Wikipedia has an article on:



Proper noun


  1. A taxonomic phylum (or division or class), within kingdom Bacteria - a group of gram-positive bacteria.

See also


Up to date as of January 23, 2010

From Wikispecies


Main Page
Superregnum: Bacteria
Regnum: Bacteria
Phylum: Actinobacteria
Classis: Actinobacteria
Subclasses: Acidimicrobidae - Actinobacteridae - Coriobacteridae - Rubrobacteridae - Sphaerobacteridae*


Actinobacteria Stackebrandt, Rainey & Ward-Rainey, 1997

Vernacular Name


  • Proposal for a new hierarchic classification system, Actinobacteria classis nov., Int. J. Syst. Bacteriol., 1997, 47, 479-491.


Subclass Sphaerobacteridae is also considered to be Class Thermomicrobia from the Chloroflexi Division, see Sphaerobacterales

Simple English

Scientific classification
Kingdom: Bacteria
Phylum: Actinobacteria
Margulis, 1974


The Actinobacteria are a group of Gram-positive bacteria. Most are found in the soil, and they include some of the most common soil life, playing important roles in decomposition and humus formation. Some form branching filaments, which somewhat resemble the mycelia of the unrelated fungi, among which they were originally classified as the Actinomycetes. All are aerobic. A few forms are pathogens, such as Mycobacterium. Some are thermophilic.


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