Streptomyces

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.

Handbook of Antibiotics
by Richard Reese, Robert Betts, Bora, Gumustop.
A popular and successful handbook and extremely useful guide to the principles of antibiotic therapy, prophylactic antibiotics, and selection of specific agents, including dosage regimens, route of administration, and duration of therapy.
(Amazon.co.UK)

The Antibiotic Paradox
by Stuart Levy.
From the leading international expert on antibiotic drugs, this text reveals how our cavalier and naive attitude about the power of antibiotics can have dire consequences. He explains that we are now witnessing a massive evolutionary change in bacteria. A build-up of new antibiotic-resistant bacteria in individuals and in the environment, mixed with the unregulated dispensing of antibiotics worldwide, is leading us into a dangerous territory where our "miracle" drugs will no longer help.
(Amazon.co.UK)