| MicrobiologyBytes: MicrobiologyBytes Video Library: Streptomyces | FAQ | Search |
The Streptomycetes are members of the bacterial order Actinomycetales, bacteria which resemble fungi in their branching filamentous structure. However, they are true bacteria - prokaryotic cells - unlike eukaryotic fungal cells. As Actinomycetes grow, they form branching filaments of cells which become a network of strands called a mycelium, similar in appearance to the mycelium of some fungi. Actinomycetes are also unique in the way they form spores and in the production of numerous antibiotics. By far the most successful genus in this group is Streptomyces with over 500 species. Few species of Streptomyces are pathogenic for animals, although a few species cause plant diseases.
This video show an environmental isolate of Streptomyces (unknown species), phase contrast microscopy, filaments ~1 µm wide, 10-100 µm long:
Actinomycetes
are non-motile, filamentous, Gram-positive bacteria.
Streptomyces species produce spores from aerial filaments called
sporophores. These rise above the colony and form spores called
conidia by simple cross-wall divisions of the filament. You
can see the refractile spores on the video. Note that this
process is distinct from the formation of bacterial endospores.
Streptomyces species are found worldwide in soil and are important
in soil ecology. Much of the characteristic earthy smell of soils arises from
chemicals called geosmens given off by Streptomyces
species. Streptomycetes are metabolically diverse and can "eat" almost
anything, including sugars, alcohols, amino acids, organic acids, and aromatic
compounds. This is achieved by producing extracellular hydrolytic
enzymes. There is considerable interest in these organisms as agents
for bioremediation.
Streptomycetes are also of medical and industrial importance because they synthesize antibiotics. There are several theories to may explain antibiotic production, the most widely accepted one being that antibiotics help the organism compete with other organisms in the relatively nutrient-depleted environment of the soil by reducing competition. Over 50 different antibiotics have been isolated from Streptomycetes species, including streptomycin, neomycin, chloramphenicol and tetracyclines.
Online Tutorial: Domagk, Fleming, Waksman & the Third Man: An interactive multimedia tutorial about antibiotics.
