Streptomyces
Streptomyces represents the largest of the Actinomycete genera, with over 500 species recognised. Streptomyces is such an important genera to humans because of their antibiotic producing abilities; it has been found that over half of the 500 species have the ability to produce antibiotics in the right conditions. It is for this reason that there has been such extensive research into the genera.
Antibiotics
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As we can see from this antibiotic discovery timeline, Streptomyces species represent a huge amount of antibiotic making organisms which have been cultured by humans. 19 antibiotic compounds out of the 34 on the timeline (Right) have been isolated from Streptomyces species. Included in this timeline are 2 specifically important antibiotics:
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The broad spectrum antibiotic Tetracycline, a crucial drug of last resort for health services battling antibiotic resistance.
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Streptomycin, which was the first antibiotic discovered by Selman Waksman and its discovery won him the Nobel prize.
Indeed it is estimated that 80% of antibiotics in use in medicine today are from the genera.
Many Streptomyces are capable of making multiple distinct antibiotics; this is accommodated by the fact that they have a large genome, frequently upwards of 8 Mega base pairs.
It is thought that Streptomyces species synthesise antibiotics due to the fact that they are most commonly found in soil habitats where they face intense competition for space and nutrients. The ability to produce antibacterial compounds gives them a competitive edge over other bacteria.
Ecology
Streptomyces tend to thrive in neutral to alkaline soils as opposed to acidic soils, as well as favouring well drained soils where conditions tend to be aerobic. Streptomyces are typically easy to culture due to their being easily cultured in a laboratory, requiring only:
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The dilution of soil with sterile water
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Spreading on selective agar
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Aerobic incubation at 25°C for 5-7 days
Morphology
Naturally as Filamentous Actinomycetes, Streptomyces produce filaments, their filaments have a branched structure due to the fact that growth occurs at the tips of these filaments. This often gives them a very tightly packed mycelium.
The aerial filaments of this genus are known are sporophores, which give rise to spores as the colony ages. In Streptomyces specifically these spores are called Conidia. The organisation of the sporophores and filaments can be very important in the identification of different Streptomyces species.
Streptomyces are not generally thought to be pathogenic to humans however they can occasionally be pathogenic to plants.
Refrences:
Madigan M, Martinko J, Stahl D, Clark D, Brock Biology of Microorganisms thirteenth edition, 557-560