streptomyces

[strep-tuh-mahy-seez]

Any of the threadlike bacteria that make up the genus Streptomyces, occurring in soil and water. These gram-positive (see gram stain), oxygen-requiring bacteria form a branching net called a mycelium that bears chains of spores at maturity. Many species are important in the decomposition of organic matter in soil, contributing in part to the earthy odour of soil and decaying leaves and to the fertility of soil. Certain species produce antibiotics such as tetracycline and streptomycin. Seealso actinomycete.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Streptomyces

Streptomyces, the largest genus of Actinobacteria and type genus of the family Streptomycetaceae. The current tally of the numbers of species is more than 500. Streptomyces, along with other Actinobacteria, is a group containing Gram-positive cell wall and genomes with high GC-content. Streptomycetes are found predominantly in soil and in decaying vegetation, and most produce spores. Streptomycetes are noted for their distinct "earthy" odor which results from production of a volatile metabolite, geosmin.

Streptomycetes are characterised by a complex secondary metabolism. They produce over two-thirds of the clinically useful antibiotics of natural origin (e.g., neomycin, chloramphenicol). The now rarely-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 such as scabies 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. At the time, the "S. coelicolor" genome was thought to contain the largest number of genes of any bacterium. The first complete genome sequence of S. avermitilis was completed in 2003. 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 2007.

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).

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. 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. 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.

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