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 Scanning electron micrograph of Actinomyces israelii.
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Actinobacteria or actinomycetes are a group of Gram-positive bacteria with high G+C ratio. 1
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Characteristics
They include some of the most common soil 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 on warmer climates.
Genera
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. Examples of organisms in this order include:
- Suborder Actinomycineae
- Family Actinomycetaceae
- Family Propionibacteriaceae
- Family Frankiaceae
- Family Micrococcaceae
- Family Micromonosporaceae
- Family Streptomycetaceae
- Suborder Corynebacterineae
- Family Mycobacteriaceae
- Family Corynebacteriaceae
- Family Nocardiaceae
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.2
Genomes of 44 different strains of Actinobacteria from different genera are either already sequenced or underway right now.citation needed
References
- ^ "MB451 Actinobacteria lecture". Retrieved on 2008-11-21.
- ^ MeSH Gardnerella
- Stackebrandt E, Rainey FA, and Ward-Rainey NL (1997). Proposal for a new hierarchic classification system, Actinobacteria classis nov. Int J Syst Bacteriol 47:479-491. Abstract
External links
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Wikispecies has information related to: Actinobacteria |
Wikipedia content modification information:
- This page was last modified on 22 December 2008, at 23:40.
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