Enhancement of secondary metabolite production using the antibiotic gradient-plate technique

We have used the antibiotic gradient-plate technique to generate antifungal producing Actinomadura strains that synthesize enhanced quantities of component 3A of a macrocyclic lactam antifungal compound Sch 38516. Seventy-nine colonies were selected from a mixture of rifampicin and spectinomycin gradient plates. The two fermentation extracts described produced an enhanced 3A component (identified with silica gel TLC, HPLC, and bioautography) when compared to the parent culture isolate extracts (no antibiotic selection).