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Morphological and Physiological Differentiation in Streptomyces

Keith F. Chater


The names of many organisms reflect their special biological properties. The name Streptomyces describes a unique morphology, albeit inaccurately: The word means “chain fungus,” although streptomycetes are undoubtedly bona fide gram-positive bacteria. The branching hyphae characteristic of Streptomyces vegetative growth form a complex substrate mycelium (Fig. 1a, b) that penetrates and solubilizes organic debris, typically in soil, by the action of extracellular hydrolytic enzymes. The inherent immobility of the mycelium is counterproductive to distribution, a problem solved (as in eukaryotic molds) by spore formation (Fig. 1c, d). Long chains of spores (often containing >50 spores) usually form from specialized aerial hyphae, which themselves apparently develop mainly by cannibalizing the vegetative mycelium. At this vulnerable stage in development, when the lysing mycelium might easily be consumed by invading motile microorganisms, it is not surprising to find that chemical defense mechanisms are employed. Indeed, nearly all of the thousands of known antibiotics are made by streptomycetes and molds, usually at a time coinciding with that of aerial mycelium formation. The idea has developed that genes for antibiotic production may therefore be subject to at least some of the regulatory mechanisms involved in setting off aerial mycelium formation and that studies of the one will provide information about the other.

In this paper descriptions of growth and morphological differentiation (first two sections) are followed by a summary of Streptomyces genetic phenomena and tools and their use in analyzing sporulation. The section, Physiological Differentiation: Production of Secondary Metabolites deals...

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