Streptomyces

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Streptomyces, from στρεπτός (streptós), meaning "twisted", and μύκης (múkés), meaning "fungus", is the largest genus of Actinomycetota, and the type genus of the family Streptomycetaceae.<ref name="Kämpfer">Template:Cite book</ref> Over 700 species of Streptomyces bacteria have been described.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=":0">Template:Cite journal</ref><ref name=":1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> As with the other Actinomycetota, streptomycetes are gram-positive, and have very large genomes with high GC content.<ref name=":0" /><ref name=Brock>Template:Cite bookTemplate:Page needed</ref> Found predominantly in soil and decaying vegetation, most streptomycetes produce spores, and are noted for their distinct "earthy" odor that results from production of a volatile metabolite, geosmin.<ref>Template:Cite book</ref> Different strains of the same species may colonize very diverse environments.<ref name=":0" />

Streptomycetes are characterised by a complex secondary metabolism.<ref name=Brock/> Between 5-23% (average: 12%) of the protein-coding genes of each Streptomyces species are implicated in secondary metabolism.<ref name=":0" /> Streptomycetes produce over two-thirds of the clinically useful antibiotics of natural origin (e.g., neomycin, streptomycin, cypemycin, grisemycin, bottromycins and chloramphenicol).<ref>Template:Cite bookTemplate:Page needed</ref><ref name="pmid24256223">Template:Cite journal</ref> The antibiotic streptomycin takes its name directly from Streptomyces. Streptomycetes are infrequent pathogens, though infections in humans, such as mycetoma, can be caused by S. somaliensis and S. sudanensis, and in plants can be caused by S. caviscabies, S. acidiscabies, S. turgidiscabies and S. scabies.

Taxonomy

When Selman Waksman and Arthur Henrici in 1943 divided Actinomyces genus into narrower genera, they failed to find a valid generic name for aerobic sporulating species so had to coin a new one.<ref>Template:Cite journal</ref>

Streptomyces is the type genus of the family Streptomycetaceae<ref name="Anderson2001">Template:Cite journal</ref> and currently covers more than 700 species with the number increasing every year.<ref name="Labeda2011">Template:Cite journal</ref><ref name=":1" /> It is estimated that the total number of Streptomyces species is close to 1600.<ref name=":0" /> Acidophilic and acid-tolerant strains that were initially classified under this genus have later been moved to Kitasatospora (1997) <ref>Template:Cite journal</ref> and Streptacidiphilus (2003).<ref>Template:Cite journal</ref> Species nomenclature are usually based on their color of hyphae and spores.

Saccharopolyspora erythraea was formerly placed in this genus (as Streptomyces erythraeus).

Morphology

The genus Streptomyces includes aerobic, Gram-positive, multicellular, filamentous bacteria that produce well-developed vegetative hyphae (between 0.5-2.0 μm in diameter) with branches. They form a complex substrate mycelium that aids in scavenging organic compounds from their substrates.<ref name=Chater/> Although the mycelia and the aerial hyphae that arise from them are amotile, mobility is achieved by dispersion of spores.<ref name=Chater/> Spore surfaces may be hairy, rugose, smooth, spiny or warty.<ref>Template:Cite journal</ref> In some species, aerial hyphae consist of long, straight filaments, which bear 50 or more spores at more or less regular intervals, arranged in whorls (verticils). Each branch of a verticil produces, at its apex, an umbel, which carries from two to several chains of spherical to ellipsoidal, smooth or rugose spores.<ref name=Chater>Template:Cite book </ref> Some strains form short chains of spores on substrate hyphae. Sclerotia-, pycnidia-, sporangia-, and synnemata-like structures are produced by some strains.

Genomics

The complete genome of "S. coelicolor strain A3(2)" was published in 2002.<ref name=Bentley_2002>Template:Cite journal</ref> At the time, the "S. coelicolor" genome was thought to contain the largest number of genes of any bacterium.<ref name=Bentley_2002/> The chromosome is 8,667,507 bp long with a GC-content of 72.1%, and is predicted to contain 7,825 protein-encoding genes.<ref name=Bentley_2002/> In terms of taxonomy, "S. coelicolor A3(2)" belongs to the species S. violaceoruber, and is not a validly described separate species; "S. coelicolor A3(2)" is not to be mistaken for the actual S. coelicolor (Müller), although it is often referred to as S. coelicolor for convenience.<ref>Template:Cite journal</ref> The transcriptome and translatome analyses of the strain A3(2) were published in 2016.<ref>Template:Cite journal</ref>

The first complete genome sequence of S. avermitilis was completed in 2003.<ref name=Ikeda_2003>Template:Cite journal</ref> Each of these genomes forms a chromosome with a linear structure, unlike most bacterial genomes, which exist in the form of circular chromosomes.<ref name="Dyson2011">Template:Cite book</ref> The genome sequence of S. scabiei, a member of the genus with the ability to cause potato scab disease, has been determined at the Wellcome Trust Sanger Institute. At 10.1 Mbp long and encoding 9,107 provisional genes, it is the largest known Streptomyces genome sequenced, probably due to the large pathogenicity island.<ref name="Dyson2011"/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The genomes of the various Streptomyces species demonstrate remarkable plasticity, via ancient single gene duplications, block duplications (mainly at the chromosomal arms) and horizontal gene transfer.<ref name=":0" /><ref>Template:Cite journal</ref> The size of their chromosome varies from 5.7-12.1 Mbps (average: 8.5 Mbps), the number of chromosomally encoded proteins varies from 4983-10,112 (average: 7130), whereas their high GC content varies from 68.8-74.7% (average: 71.7%).<ref name=":0" /> The 95% soft-core proteome of the genus consists of approximately 2000-2400 proteins.<ref name=":0" /> The pangenome is open.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> In addition, significant genomic plasticity is observed even between strains of the same species, where the number of accessory proteins (at the species level) ranges from 250 to more than 3000.<ref name=":0" /> Intriguingly, a correlation has been observed between the number of carbohydrate-active enzymes and secondary metabolite biosynthetic gene clusters (siderophores, e-Polylysin and type III lanthipeptides) that are related to competition among bacteria, in Streptomyces species.<ref name=":0" /> Streptomycetes are major biomass degraders, mainly via their carbohydrate-active enzymes.<ref>Template:Cite journal</ref> Thus, they also need to evolve an arsenal of siderophores and antimicrobial agents to suppress competition by other bacteria in these nutrient-rich environments that they create.<ref name=":0" /> Several evolutionary analyses have revealed that the majority of evolutionarily stable genomic elements are localized mainly at the central region of the chromosome, whereas the evolutionarily unstable elements tend to localize at the chromosomal arms.<ref name=":0" /><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Thus, the chromosomal arms emerge as the part of the genome that is mainly responsible for rapid adaptation at both the species and strain level.<ref name=":0" />

Biotechnology

Biotechnology researchers have used Streptomyces species for heterologous expression of proteins. Traditionally, Escherichia coli was the species of choice to express eukaryotic genes, since it was well understood and easy to work with.<ref name=Brawner_1991>Template:Cite journal</ref><ref name=Payne_1990>Template:Cite journal</ref> Expression of eukaryotic proteins in E. coli may be problematic. Sometimes, proteins do not fold properly, which may lead to insolubility, deposition in inclusion bodies, and loss of bioactivity of the product.<ref name=Binnie_1997>Template:Cite journal</ref> Though E. coli strains have secretion mechanisms, these are of low efficiency and result in secretion into the periplasmic space, whereas secretion by a Gram-positive bacterium such as a Streptomyces species results in secretion directly into the extracellular medium. In addition, Streptomyces species have more efficient secretion mechanisms than E.coli. The properties of the secretion system is an advantage for industrial production of heterologously expressed protein because it simplifies subsequent purification steps and may increase yield. These properties among others make Streptomyces spp. an attractive alternative to other bacteria such as E. coli and Bacillus subtilis.<ref name="Binnie_1997"/> In addition, the inherently high genomic instability suggests that the various Streptomycetes genomes may be amenable to extensive genome reduction for the construction of synthetic minimal genomes with industrial applications.<ref name=":0" />

Plant pathogenic bacteria

Several species belonging to this genus have been found to be pathogenic to plants:<ref name=Labeda2011/>

1. S. scabiei
2. S. acidiscabies
3. S. europaeiscabiei
4. S. luridiscabiei
5. S. niveiscabiei
6. S. puniciscabiei
7. S. reticuliscabiei
8. S. stelliscabiei
9. S. turgidiscabies (scab disease in potatoes)
10. S. ipomoeae (soft rot disease in sweet potatoes)
11. S. brasiliscabiei (first species identified in Brazil)<ref>Template:Cite journal</ref>
12. S. hilarionis and S. hayashii (new species identified in Brazil)<ref>Template:Cite journal</ref>

Medicine

Streptomyces is the largest antibiotic-producing genus, producing antibacterial, antifungal, and antiparasitic drugs, and also a wide range of other bioactive compounds, such as immunosuppressants.<ref name="pmid11702082">Template:Cite journal</ref> Almost all of the bioactive compounds produced by Streptomyces are initiated during the time coinciding with the aerial hyphal formation from the substrate mycelium.<ref name=Chater/>

Antifungals

Template:See also Streptomycetes produce numerous antifungal compounds of medicinal importance, including nystatin (from S. noursei), amphotericin B (from S. nodosus),<ref name="pmid22975171">Template:Cite journal</ref> and natamycin (from S. natalensis).

Antibacterials

Members of the genus Streptomyces are the source for numerous antibacterial pharmaceutical agents; among the most important of these are:

• Chloramphenicol (from S. venezuelae)<ref>Template:Cite journal</ref>
• Daptomycin (from S. roseosporus)<ref>Template:Cite journal</ref>
• Fosfomycin (from S. fradiae)<ref name="pmid17113999">Template:Cite journal</ref>
• Lincomycin (from S. lincolnensis)<ref>Template:Cite journal</ref>
• Neomycin (from S. fradiae)<ref>Template:Cite journal</ref>
• Nourseothricin Template:Citation needed
• Puromycin (from S. alboniger)<ref>Template:Cite journal</ref>
• Streptomycin (from S. griseus)<ref>Template:Cite journal</ref>
• Tetracycline (from S. rimosus and S. aureofaciens)<ref name="NelsonGreenwald2001">Template:Cite book</ref>
• Oleandomycin (from S. antibioticus)<ref>{{#invoke:citation/CS1|citation

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• Tunicamycin (from S. torulosus)<ref>Template:Cite journal</ref>
• Mycangimycin (from Streptomyces sp. SPB74 and S. antibioticus)<ref>Template:Cite journal</ref>
• Boromycin (from S. antibioticus)<ref>Template:Cite journal</ref>
• Bambermycin (from S. bambergiensis and S. ghanaensis, the active compound being moenomycins A and C)<ref>{{#invoke:citation/CS1|citation

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• Vulgamycin<ref>Template:Cite journal</ref>

Clavulanic acid (from S. clavuligerus) is a drug used in combination with some antibiotics (like amoxicillin) to block and/or weaken some bacterial-resistance mechanisms by irreversible beta-lactamase inhibition. Novel antiinfectives currently being developed include Guadinomine (from Streptomyces sp. K01-0509),<ref name="Holmes2012">Template:Cite journal</ref> a compound that blocks the Type III secretion system of Gram-negative bacteria.

Antiparasitic drugs

S. avermitilis is responsible for the production of one of the most widely employed drugs against nematode and arthropod infestations, avermectin,<ref name="Martin-et-al-2017">Template:Cite journal</ref> and thus its derivatives including ivermectin.

Other

File:Saptomycin D and E Structures.svg

Saptomycins D and E

Less commonly, streptomycetes produce compounds used in other medical treatments: migrastatin (from S. platensis) and bleomycin (from S. verticillus) are antineoplastic (anticancer) drugs; boromycin (from S. antibioticus) exhibits antiviral activity against the HIV-1 strain of HIV, as well as antibacterial activity. Staurosporine (from S. staurosporeus) also has a range of activities from antifungal to antineoplastic (via the inhibition of protein kinases).

S. hygroscopicus and S. viridochromogenes produce the natural herbicide bialaphos.

Saptomycins and Legonmycins are chemical compounds isolated from Streptomyces.<ref>Template:Cite journal</ref>

Symbiosis

Sirex wasps cannot perform all of their own cellulolytic functions and so some Streptomyces do so in symbiosis with the wasps.<ref name="Li-et-al-2021">Template:Cite journal</ref> Book et al. have investigated several of these symbioses.<ref name="Li-et-al-2021" /> Book et al., 2014 and Book et al., 2016 identify several lytic isolates.<ref name="Li-et-al-2021" /> The 2016 study isolates Streptomyces sp. Amel2xE9 and Streptomyces sp. LamerLS-31b and finds that they are equal in activity to the previously identified Streptomyces sp. SirexAA-E.<ref name="Li-et-al-2021" />

See also

• Antimycin A – Chemical compound produced by Streptomyces used as a piscicide
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• Streptomyces isolates
• List of bacterial orders
• List of bacteria genera
• raiA-hairpin RNA motif

Further reading

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External links

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