Streptomyces

Streptomyces is the largest genus of Actinobacteria, Gram-positive bacteria. Streptomyces is often found in soil and is very much similar to fungi by its shape. They form long thin threads called hyphae that can differentiate into a chain of spores for reproduction. Almost all of the bioactive compounds produced by Streptomyces are made while the hyphae are forming from the substrate mycelium.

Streptomyces
S. griseus - a species of Streptomyces genus
Scientific classification
Kingdom:	Bacteria
Phylum:	Actinomycetota
Class:	Actinomycetia
Order:	Streptomycetales
Family:	Streptomycetaceae
Genus:	Streptomyces Waksman & Henrici 1943

Use in medicine and science

Streptomyces are medically important, as they produce antifungals, antiparasitic drugs, antivirals, antitumorals, anti-hypertensives, immunosuppressants and antibiotics. Different species of streptomyces are used to produce different antibiotics. Over 500 species of Streptomyces bacteria have been described. For example, widely studied S. griseus was the first to be used in production of an antibiotic streptomycin, while S. avermitilis as a source of avermictin. Another well-studied species, S coelicolor, is widely used in genetic studies due to its relative ease of handling and distinct morphological stages. Overall, Streptomyces produce over two-thirds of the clinically useful antibiotics of natural origin, such as tetracycline, neomycin and chloramphenicol.

Slide culture of a Streptomyces species

Antibiotic mechanism

Antibiotics target essential proteins for pathogens’ growth and survival, inhibiting essential functions. For example, streptomycin, which is made from S. griseus, irreversibly binds to bacterial genetic material and causes errors in the production of new proteins, which leads to cell death. It can be used for treating severe infections, such as tuberculosis and plague. Another example is avermectin, made from S. avermitili. It causes invertebrate paralysis (inability to make and pass nerve impulses), which is used as a drug and pesticide against parasitic worms and insects. Avermectin enhances glutamate (neurotransmitter) at the glutamate-gated chloride channels that mammals don’t possess. It causes the excess of chloride ions inside the cell (hyperpolarisation), so the action potential cannot be further induced, ultimately leading to paralysis.

Antibiotic resistance

Genetic changes in bacteria might result in antibiotic resistance. They might be acquired through spontaneous mutations (vertical gene transfer) or through other bacteria passing their genes (horizontal gene transfer). Self-medications or improper medication use can result in the emergence of resistant bacteria. It is difficult to obtain new antibiotics, that is why researchers seek to improve existing ones, as well as working to discover new drugs.

Streptomyces Media

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  Mycelial sheets 
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  The chemical structures of Saptomycin D and E