Actinobacteria
Encyclopedia
Actinobacteria are a group of Gram-positive
bacteria
with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria.
Use of the ferric uptake regulator (fur) has been suggested for classification. Analysis of glutamine synthetase
has also been suggested.
, 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 pathogen
s, 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 microorganism
s, 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 spore
s.
Some types of Actinobacteria are responsible for the peculiar odor emanating from the soil after rain (Petrichor
), mainly in warmer climates. The chemical that produces this odour is known as Geosmin
.
, 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.
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria.
Use of the ferric uptake regulator (fur) has been suggested for classification. Analysis of glutamine synthetase
Glutamine synthetase
Glutamine synthetase is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:Glutamate + ATP + NH3 → Glutamine + ADP + phosphate...
has also been suggested.
Characteristics
Actinobacteria include some of the most common soil lifeSoil life
Soil life or soil biota is a collective term for all the organisms living within the soil.-Overview:In balanced soil, plants grow in an active and steady environment. The mineral content of the soil and its heartiful structure are important for their well-being, but it is the life in the earth that...
, freshwater life, and marine life, playing an important role in decomposition of organic materials, such as cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
and chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
, and thereby playing a vital part in organic matter turnover and carbon cycle
Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
. 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 pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s, such as Mycobacterium
Mycobacterium
Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis and leprosy...
, Corynebacterium
Corynebacterium
Corynebacterium is a genus of Gram-positive rod-shaped bacteria. They are widely distributed in nature and are mostly innocuous. Some are useful in industrial settings such as C. glutamicum. Others can cause human disease. C...
, Nocardia
Nocardia
Nocardia is a genus of weakly staining Gram-positive, catalase-positive, rod-shaped bacteria. It forms partially acid-fast beaded branching filaments . It has a total of 85 species. Some species are non-pathogenic while others are responsible for nocardiosis. Nocardia are found worldwide in soil...
, Rhodococcus
Rhodococcus
Rhodococcus is a genus of aerobic, nonsporulating, nonmotile Gram-positive bacteria closely related to Mycobacteria and Corynebacteria. While a few species are pathogenic, most are benign and have been found to thrive in a broad range of environments, including soil, water, and eukaryotic cells...
and a few species of Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
.
Actinobacteria are well known as secondary metabolite
Secondary metabolite
Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolities does not result in immediate death, but rather in long-term impairment of the organism's...
producers and hence of high pharmacological and commercial interest. In 1940 Selman Waksman
Selman Waksman
Selman Abraham Waksman was an American biochemist and microbiologist whose research into organic substances—largely into organisms that live in soil—and their decomposition promoted the discovery of Streptomycin, and several other antibiotics...
discovered that the soil bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
he was studying made actinomycin
Actinomycin
The actinomycins are a class of polypeptide antibiotics isolated from soil bacteria of the genus Streptomyces, of which the most significant is actinomycin D. It was the first antibiotic isolated by Selman Waksman and his co-worker H. B. Woodruff in 1940.-Mechanism:Actinomycin D is primarily used...
, a discovery for which he received a Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
. Since then, hundreds of naturally occurring antibiotics have been discovered in these terrestrial microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s, especially from the genus Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
.
Some Actinobacteria form branching filaments, which somewhat resemble the mycelia
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
of the unrelated fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
, among which they were originally classified under the older name Actinomycetes. Most members are aerobic
Aerobic organism
An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.Faculitative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.-Glucose:...
, but a few, such as Actinomyces israelii, can grow under anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...
conditions. Unlike the Firmicutes
Firmicutes
The Firmicutes are a phylum of bacteria, most of which have Gram-positive cell wall structure. A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative...
, the other main group of Gram-positive bacteria, they have DNA with a high GC-content
GC-content
In molecular biology and genetics, GC-content is the percentage of nitrogenous bases on a DNA molecule that are either guanine or cytosine . This may refer to a specific fragment of DNA or RNA, or that of the whole genome...
, and some Actinomycetes species produce external spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s.
Some types of Actinobacteria are responsible for the peculiar odor emanating from the soil after rain (Petrichor
Petrichor
Petrichor is the scent of rain on dry earth. The word is constructed from Greek, petra, meaning stone + ichor, the fluid that flows in the veins of the gods in Greek mythology....
), mainly in warmer climates. The chemical that produces this odour is known as Geosmin
Geosmin
Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather or when soil is...
.
Genera
Most Actinobacteria of medical or economic significance are in subclass ActinobacteridaeActinobacteridae
Actinobacteridae is a subclass of bacteria, in the class of Actinobacteria.The group is diverse. Examples of organisms in this taxon include:* Suborder Actinomycineae** Family Actinomycetaceae*** Actinomyces** Family Propionibacteriaceae...
, order Actinomycetales
Actinomycetales
Actinomycetales is an order of Actinobacteria. They are very diverse and contain a variety of subdivisions as well as yet unclassified isolates. This is mainly because some genera are very difficult to classify because of a highly niche-dependent phenotype...
. While many of these cause disease in humans, Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
is notable as a source of antibiotics.
Of those Actinobacteria not in Actinomycetales, Gardnerella
Gardnerella
Gardnerella is a genus of gram-variable-staining facultative anaerobic bacteria of which G. vaginalis is the only species.Once classified as Haemophilus vaginalis and afterwards as Corynebacterium vaginalis, Gardnerella vaginalis grows as small, circular, convex, gray colonies on chocolate agar; it...
is one of the most researched. Classification of Gardnerella is controversial, and MeSH
Medical Subject Headings
Medical Subject Headings is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences; it can also serve as a thesaurus that facilitates searching...
catalogues it as both a gram-positive
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
and gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
organism.