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The Actinomycetales are an
order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...

order
of
Actinobacteria The Actinobacteria are a phylum of mostly Gram-positive bacteria File:Gram stain 01.jpg, 300px, Violet-stained gram-positive cocci and pink-stained gram-negative bacillus (shape), bacilli In bacteriology, gram-positive bacteria are bacteria tha ...
. A member of the order is often called an actinomycete. The actinomycetes are diverse and contain a variety of subdivisions, as well as yet-unclassified isolates, mainly because some genera are difficult to classify because of a highly niche-dependent
phenotype In genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...

phenotype
. For example, ''
Nocardia ''Nocardia'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a ...

Nocardia
'' contains several phenotypes first believed to be distinct species before their differences were shown to be entirely dependent on their growth conditions. Actinomycetales are generally gram-positive and anaerobic and have mycelium in a filamentous and branching growth pattern. Some actinobacteria can form rod- or coccoid-shaped forms, while others can form spores on aerial
hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by a ...
. Actinomycetales bacteria can be infected by
bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, ...

bacteriophage
s, which are called actinophages. Actinomycetales can range from harmless bacteria to pathogens with resistance to antibiotics.


Difficulty of classification

Actinomycetales are
Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
, but several species have complex
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
structures that make the
Gram stain Gram stain or Gram staining, also called Gram's method, is a method of staining specimen, sandwiched between a glass microscope slide. Staining is a technique used to enhance contrast in samples, generally at the Microscope, microscopic leve ...

Gram stain
ing unsuitable (e.g.
Mycobacteriaceae ''Mycobacterium'' is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. Over 190 species are recognized in this genus. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (''Mycobact ...
). Actinomycetales have
prokaryotic A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual conti ...
nuclei ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...
, are susceptible to
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
, and have cell walls that contain
muramic acid Muramic acid is an amino sugar acid. In terms of chemical composition, it is the ether Ethers are a class of organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds ...

muramic acid
. Actinomycetales have the appearance of filaments or
hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by a ...

hyphae
, superficially resembling many forms of hyphal fungi.


Reproduction

Actinomycetales have 2 main forms of reproduction;
spore In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
formation and hyphae fragmentation. During reproduction, Actinomycetales can form conidiophores, sporangiospores, and oidiospores. In reproducing through hyphae fragmentation, the hyphae formed by Actinomycetales can be a fifth to half the size of fungal hyphae, and bear long spore chains.


Presence and associations

Actinomycetales can be found mostly in soil and decaying organic matter, as well as in living organisms such as humans and animals. They form symbiotic
nitrogen fixing Nitrogen fixation is a chemical process by which molecular nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific st ...
associations with over 200 species of plants, and can also serve as growth promoting or biocontrol agents, or cause disease in some species of plants. Actinomycetales can be found in the human
urogenital The genitourinary system, or urogenital system, are the organs of the reproductive system and the urinary system The urinary system, also known as the renal system or urinary tract, consists of the kidneys, ureters, bladder The urinary bl ...
tract as well as in the
digestive system The human digestive system consists of the human gastrointestinal tract, gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food in ...

digestive system
including the mouth, throat, and
gastrointestinal The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organs of the digestive system The human digestive system consists of the human ...
tract in the form of Helicobacter without causing disease in the host. They also have wide medicinal and
botanical Botany, also called , plant biology or phytology, is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A ...
applications, and are used as a source of many
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
and
pesticides Pesticides are substances that are meant to control pests Pest or The Pest may refer to: Science and medicine * Pest (organism), an animal or plant detrimental to humans or human concerns ** Weed, a plant considered undesirable * Infectious d ...
.


Antimicrobial properties

Many species of Actinomycetes produce antimicrobial compounds under certain conditions and growth media.
Streptomycin Streptomycin is an antibiotic medication used to treat a number of bacterial infections. This includes tuberculosis, Mycobacterium avium complex, ''Mycobacterium avium'' complex, endocarditis, brucellosis, Burkholderia infection, ''Burkholderia' ...

Streptomycin
,
actinomycin Dactinomycin, also known as actinomycin D, is a chemotherapy medication used to treat a number of types of cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or Metastasis, spread to other part ...

actinomycin
, and streptothricin are all medically important antibiotics isolated from Actinomycetes bacteria. Almost two-thirds of the natural antimicrobial drug compounds used currently are produced by different species of Actinomycetes.


See also

*
Actinobacteria#Phylogeny
Actinobacteria#Phylogeny
, shows about 20 species


References

* See the
NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The N ...
br>webpage on Actinomycetales
Data extracted from the * * {{Taxonbar, from=Q343452 Actinobacteridae