HALLIE'S NOTES
Actinomyces griseus is a synonym for Streptomyces griseus.
Streptomyces griseus produces the anti-cancer drug streptocin.
Respiration: Aerobic
Gram Stain: Positive
Growth Temperature: 26oC
Antibiotics synthesized by the soil organism Streptomyces griseus. Streptomycin was discovered by American biochemists Selman Waksman, Albert Schatz, and Elizabeth Bugie in 1943. The drug acts by interfering with the ability of a microorganism to synthesize certain vital proteins. It was the first antimicrobial agent developed after penicillin and the first antibiotic effective in treating tuberculosis. Because it was effective against a wide variety of diseases, streptomycin was used often, with the result that many initially sensitive microorganisms, including the bacterium that causes tuberculosis, became resistant to the antibiotic. It is used in combination with penicillin for treating infections of heart valves (endocarditis) and with tetracyclines in the treatment of plague, tularemia, and brucellosis.
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History
Many of the antibiotics used today are made by a group of bacteria called Streptomyces. Streptomycetes evolved about 450 million years ago as branched filamentous organisms adapted to the utilization of plant remains. They reproduce by sending up specialized aerial branches, which form spores. Aerial growth is parasitic on the primary colony, which is digested and reused for aerial growth. The reproductive phase is coordinated with the secretion of antibiotics, which may protect the colony against invading bacteria during aerial growth. A clue to the integration of antibiotic production and aerial growth is provided by bldA mutants, which are defective in both processes. These mutants lack the ability to translate a particularly rare codon, UUA, in the genetic code. The UUA codon (TTA in DNA) is present in several regulatory genes that control sets of antibiotic production genes, and in one, bldH that controls aerial mycelium formation. The regulatory genes for antibiotic production are all involved in self-reinforcing regulatory systems that potentially amplify the regulatory significance of small changes in the efficiency of translation of UUA codons. One of the regulatory targets of bldH is an extracellular protease inhibitor protein that is likely to delay the digestion of the primary biomass until the colony is ready for aerial growth. The use of the UUA codon to orchestrate different aspects of extracellular biology appeared very early in Streptomyces evolution
Amazing Facts
Streptomycetes are the most important source of antibiotics for medical, veterinary and agricultural use. They belong to a class of bacteria of considerable interest to human welfare that are known as actinomycetes. This name, meaning ‘ray fungi’, was conferred because the first known example grew as fungus-like branching filaments, but actinomycetes are now known to encompass various forms. The simplest are unicellular spheres and rods, among which are the corynebacteria, including the agent of diphtheria as well as more benign industrial species used to make amino acids for food supplementation. Other actinomycetes are somewhat filamentous, including the mycobacteria that cause tuberculosis and leprosy. Members of the genus Streptomyces are the most complex: they grow as a mycelium of branching hyphal filaments, and reproduce in a mould-like manner by sending up aerial branches that turn into chains of spores. The coordination of this morphological development with both antibiotic production and other aspects of extracellular biology is the subject of this article.
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