streptomyces

Streptomyces
Slide culture of a Streptomyces sp.
Scientific classification
Domain: Bacteria Phylum: Actinobacteria Order: Actinomycetales Family: Streptomycetaceae Genus: Streptomyces Waksman & Henrici 1943
Species
S. achromogenes S. ambofaciens S. aureofaciens S. avermitilis S. clavuligerus S. coelicolor S. felleus S. ferralitis S. filamentosus S. griseus S. hygroscopicus S. iysosuperficus S. lividans S. noursei S. scabies S. somaliensis S. thermoviolaceus S. toxytricini S. tsukubaensis S. venezuelae S. violaceoruber plus ~500 additional species.

Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae.^[1] Over 500 species of Streptomyces bacteria have been described.^[2] As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high GC-content.^[3] Found predominantly in soil and decaying vegetation, most streptomycetes produce spores, and are noted for their distinct "earthy" odor which results from production of a volatile metabolite, geosmin.

Streptomycetes are characterised by a complex secondary metabolism.^[3] They produce over two-thirds of the clinically useful antibiotics of natural origin (e.g., neomycin, chloramphenicol).^[4] The now uncommonly-used streptomycin takes its name directly from Streptomyces. Streptomycetes are infrequent pathogens, though infections in human such as mycetoma can be caused by S. somaliensis and S. sudanensis and in plants can be caused by S. caviscabies and S. scabies.

Genomics

The complete genome of one of the strain, "S. coelicolor" A3(2), was published in 2002.^[5] At the time, the "S. coelicolor" genome was thought to contain the largest number of genes of any bacterium.^[5] 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.^[5] Taxonomically, "S. coelicolor" A3(2) belongs to the species of S. violaceoruber and not a validly described separate species; "S. coelicolor" A3(2) is not to be mistaken for S. coelicolor (Müller) (ATCC 23899).

The first complete genome sequence of S. avermitilis was completed in 2003.^[6] Each of these genomes form a chromosome with a linear structure, unlike most bacterial genomes which exist in the form of circular chromosomes. The genome sequence of S. scabies, a member of the genus with the ability to cause potato scab disease, has been determined at the Wellcome Trust Sanger Institute and is currently in annotation, with publication scheduled for 2009.

Biotechnology

In recent years, biotechnology researchers have begun to use Streptomyces spp. for production of recombinant human proteins. Traditionally, Escherichia coli was the species of choice to host eukaryotic genes since it was well understood and easy to work with.^[7][8] However, E. coli introduces problems such as incorrect (or lack of) glycosylation and incorrect protein folding, resulting in insolubility and loss of bioactivity of the product.^[9] Streptomyces spp. on the other hand have the ability to secrete correctly folded recombinant proteins into the medium after production simplifying the subsequent purification steps. These properties among others make Streptomyces spp. an attractive alternative to other bacteria such as E. coli and Bacillus subtilis.^[9]

Medicine

Streptomyces is the largest antibiotic producing genus, producing both antibacterials and antifungals, and also a wide range of other bioactive compounds such as immunosuppressants.^[10]

Antifungals

Streptomycetes produce numerous antifungal compounds of medicinal importance, including nystatin (from S. noursei), amphotericin B (from S. nodosus), and natamycin (from S. natalensis).

Antibacterials

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

• Erythromycin (from Saccharopolyspora erythrea, formerly known as S. erythraeus)
• Neomycin (from S. fradiae)
• Streptomycin (from S. griseus)
• Tetracycline (from S. rimosus)
• Vancomycin (from S. orientalis)
• Daptomycin (from S. roseosporus)
• Rifamycin (from S. mediterranei)
• Chloramphenicol (from S. venezuelae)
• Puromycin (from S. alboniger)
• Lincomycin (from S. lincolnensis)
• Cefoxitin (from S. lactamdurans)

Antiparasitic drugs

S. avermitilis is responsible for the production of one of the most widely employed drugs against nematode and arthropod infestations, ivermectin.

Other

Less commonly, streptomycetes produce compounds used in other medical treatments: migrastatin (from S. platensis) is an antineoplastic (anti-cancer) drug.

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

See also

• Antimycin A - compound produced by this bacteria used in piscicides.

References

Further reading

• Baumberg S (1991). Genetics and Product Formation in Streptomyces. Kluwer Academic. ISBN 978-0306438851. 
• Gunsalus IC (1986). Bacteria: Antibiotic-producing Streptomyces. Academic Press. ISBN 978-0123072092. 
• Hopwood DA (2007). Streptomyces in Nature and Medicine: The Antibiotic Makers. Oxford University Press. ISBN 978-0195150667. 

External links

• Current research on Streptomyces coelicolor at the Norwich Research Park
• Some current Streptomyces Research & Methods / Protocols / Resources
• S. avermitilis genome homepage (Kitasato Institute for Life Sciences)
• S. coelicolor A3(2) genome homepage (Sanger Institute)
• Streptomyces.org.uk homepage (John Innes Centre)
• StrepDB - the Streptomyces genomes annotation browser
• Streptomyces Genome Projects from Genomes OnLine Database