Actinobacteria

Actinobacteria
Scanning electron micrograph of Actinomyces israelii.
Scientific classification
Domain:	Bacteria
Phylum:	Actinobacteria Margulis
Class:	Actinobacteria
Subclasses/Orders
Acidimicrobidae Acidimicrobiales Contains one genus Acidimicrobium Actinobacteridae Actinomycetales Bifidobacteriales Coriobacteridae Coriobacterales Contains one family Coriobacteriaceae Rubrobacteridae Rubrobacterales Contains one genus Rubrobacter Sphaerobacteridae Sphaerobacterales Contains one genus Sphaerobacter

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]

Characteristics

They include some of the most common soil life, freshwater life, 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 for which he received 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]

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.

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.

References

External links

• Effects of transgenic T4 lysozyme potato plants on micro-organisms in the soil – focusing on bacteria and fungi in the rhizosphere
• Actinomycetes genome database