The filamentous soil bacteria actinomycetes are a rich source of natural product antibiotics. The structural variety and broad range of associated biological activities of the molecules isolated from these organisms are astonishing. The diverse geographical locations from which these organisms have been isolated, exotic and not so exotic, attest to the keen interest the pharmaceutical industry has for these soil bacteria [1]. Over the past 50 years natural product antibiotics have revolutionized the practice of modern medicine so that it is difficult to imagine a world without them. Surprisingly, the actinomycetes (family: Actinomycetales) are a relatively small and closely related group of bacteria given the molecular diversity of the compounds they produce.

In the past, researchers combed the world to discover greater microbial and molecular diversity. Screening actinomycetes isolated from soil samples from Easter Island and Puerto Rico resulted in the discovery of immunosupressant rapamycin and erythromycin, respectively. A strain from Texas yielded tetracy-cline. Other strains that produced penicillin N, clavulonic acid, and the enediyne antitumor agent esperamycin A1 were found in South America (Fig. 1).

Over time, this traditional approach to natural products discovery became perceived as one of diminishing return due to inherent problems associated with

Figure 1 Structure of some actinomycete natural products.

Tetracycline Clavulonic acid

Figure 1 Structure of some actinomycete natural products.

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