Streptomyces, from στρεπτός (streptós), meaning "twisted", and μύκης (múkés), meaning "fungus", is the largestgenus ofActinomycetota, and thetype genus of the familyStreptomycetaceae.[3] Over 700 species ofStreptomycesbacteria have been described.[4][5][6] As with the other Actinomycetota, streptomycetes aregram-positive, and have very largegenomes with highGC content.[5][7] Found predominantly in soil and decaying vegetation, most streptomycetes producespores, and are noted for their distinct "earthy" odor that results from production of a volatilemetabolite,geosmin.[8] Different strains of the same species may colonize very diverse environments.[5]
WhenSelman Waksman and Arthur Henrici in 1943 dividedActinomyces genus into narrower genera, they failed to find a valid generic name for aerobic sporulating species so had to coin a new one.[11]
Streptomyces is the type genus of the familyStreptomycetaceae[12] and currently covers more than 700species with the number increasing every year.[13][6] It is estimated that the total number ofStreptomyces species is close to 1600.[5]Acidophilic and acid-tolerant strains that were initially classified under this genus have later been moved toKitasatospora (1997)[14] andStreptacidiphilus (2003).[15] Species nomenclature are usually based on their color ofhyphae andspores.
The genusStreptomyces includesaerobic,Gram-positive, multicellular, filamentous bacteria that produce well-developed vegetative hyphae (between 0.5-2.0 μm in diameter) with branches. They form a complexsubstrate mycelium that aids in scavenging organic compounds from their substrates.[16] Although the mycelia and theaerial hyphae that arise from them are amotile, mobility is achieved by dispersion of spores.[16] Spore surfaces may be hairy, rugose, smooth, spiny or warty.[17] 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.[16] Some strains form short chains of spores on substrate hyphae. Sclerotia-, pycnidia-, sporangia-, and synnemata-like structures are produced by some strains.
The completegenome of "S. coelicolor strain A3(2)" was published in 2002.[18] At the time, the "S. coelicolor" genome was thought to contain the largest number ofgenes of anybacterium.[18] The chromosome is 8,667,507bp long with a GC-content of 72.1%, and is predicted to contain 7,825 protein-encoding genes.[18] In terms of taxonomy, "S. coelicolor A3(2)" belongs to the speciesS. violaceoruber, and is not a validly described separate species; "S. coelicolor A3(2)" is not to be mistaken for the actualS. coelicolor (Müller), although it is often referred to asS. coelicolor for convenience.[19] The transcriptome and translatome analyses of the strain A3(2) were published in 2016.[20]
The first complete genome sequence ofS. avermitilis was completed in 2003.[21] Each of these genomes forms achromosome with a linear structure, unlike most bacterial genomes, which exist in the form of circular chromosomes.[22] The genome sequence ofS. scabiei, a member of the genus with the ability to cause potato scab disease, has been determined at theWellcome Trust Sanger Institute. At 10.1 Mbp long and encoding 9,107 provisional genes, it is the largest knownStreptomyces genome sequenced, probably due to the largepathogenicity island.[22][23]
The genomes of the variousStreptomyces species demonstrate remarkable plasticity, via ancient single gene duplications, block duplications (mainly at the chromosomal arms) and horizontal gene transfer.[5][24] 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%).[5] The 95% soft-core proteome of the genus consists of approximately 2000-2400 proteins.[5] Thepangenome is open.[25][26] 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.[5] Intriguingly, a correlation has been observed between the number of carbohydrate-active enzymes and secondary metabolite biosynthetic gene clusters (siderophores, e-Polylysin and type IIIlanthipeptides) that are related to competition among bacteria, inStreptomyces species.[5] Streptomycetes are major biomass degraders, mainly via their carbohydrate-active enzymes.[27] 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.[5] 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.[5][28][29][30][31] 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.[5]
Biotechnology researchers have usedStreptomyces species forheterologous expression of proteins. Traditionally,Escherichia coli was the species of choice to expresseukaryotic genes, since it was well understood and easy to work with.[32][33] Expression of eukaryotic proteins inE. coli may be problematic. Sometimes, proteins do not fold properly, which may lead to insolubility, deposition ininclusion bodies, and loss of bioactivity of the product.[34] ThoughE. coli strains have secretion mechanisms, these are of low efficiency and result in secretion into theperiplasmic space, whereas secretion by a Gram-positive bacterium such as aStreptomyces species results in secretion directly into the extracellular medium. In addition,Streptomyces species have more efficient secretion mechanisms thanE.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 makeStreptomyces spp. an attractive alternative to other bacteria such asE. coli andBacillus subtilis.[34] 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.[5]
Streptomyces is the largestantibiotic-producing genus, producing antibacterial,antifungal, and antiparasitic drugs, and also a wide range of otherbioactive compounds, such asimmunosuppressants.[37] Almost all of the bioactive compounds produced byStreptomyces are initiated during the time coinciding with the aerial hyphal formation from the substrate mycelium.[16]
Clavulanic acid (fromS. clavuligerus) is a drug used in combination with some antibiotics (likeamoxicillin) to block and/or weaken some bacterial-resistance mechanisms by irreversible beta-lactamase inhibition.Novel antiinfectives currently being developed includeGuadinomine (fromStreptomyces sp. K01-0509),[55] a compound that blocks theType III secretion system of Gram-negative bacteria.
S. avermitilis is responsible for the production of one of the most widely employed drugs against nematode and arthropod infestations,avermectin,[56] and thus its derivatives includingivermectin.
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^Kim SB, Lonsdale J, Seong CN, Goodfellow M (2003). "Streptacidiphilus gen. nov., acidophilic actinomycetes with wall chemotype I and emendation of the family Streptomycetaceae (Waksman and Henrici (1943)AL) emend. Rainey et al. 1997".Antonie van Leeuwenhoek.83 (2):107–16.doi:10.1023/A:1023397724023.PMID12785304.S2CID12901116.
^Chen CW, Huang CH, Lee HH, Tsai HH, Kirby R (October 2002). "Once the circle has been broken: dynamics and evolution of Streptomyces chromosomes".Trends in Genetics.18 (10):522–529.doi:10.1016/s0168-9525(02)02752-x.PMID12350342.
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^Payne GF, DelaCruz N, Coppella SJ (July 1990). "Improved production of heterologous protein from Streptomyces lividans".Applied Microbiology and Biotechnology.33 (4):395–400.doi:10.1007/BF00176653.PMID1369282.S2CID19287805.
^abBinnie C, Cossar JD, Stewart DI (August 1997). "Heterologous biopharmaceutical protein expression in Streptomyces".Trends in Biotechnology.15 (8):315–20.doi:10.1016/S0167-7799(97)01062-7.PMID9263479.
^Corrêa DB, do Amaral DT, da Silva MJ, Destéfano SA (July 2021). "Streptomyces brasiliscabiei, a new species causing potato scab in south Brazil".Antonie van Leeuwenhoek.114 (7):913–931.doi:10.1007/s10482-021-01566-y.PMID33881637.
^Vitor L, Amaral DT, Corrêa DB, Ferreira-Tonin M, Lucon ET, Appy MP, et al. (June 2023). "Streptomyces hilarionis sp. nov. andStreptomyces hayashii sp. nov., two new strains associated with potato scab in Brazil".International Journal of Systematic and Evolutionary Microbiology.73 (6).doi:10.1099/ijsem.0.005916.PMID37319004.
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^Swan DG, Rodríguez AM, Vilches C, Méndez C, Salas JA (February 1994). "Characterisation of a Streptomyces antibioticus gene encoding a type I polyketide synthase which has an unusual coding sequence".Molecular & General Genetics.242 (3):358–62.doi:10.1007/BF00280426.hdl:10651/41900.PMID8107683.S2CID2195072.
