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Effects of Metals on Streptomyces coelicolor Growth and Actinorhodin Production

Actinorhodin production by Streptomyces coelicolor was used as a model system to study the effects of metals on growth and polyketide synthesis in a streptomycete. Numerous metals were tested in cultures grown in liquid media. Mercury and cadmium were highly toxic, and copper, nickel, and lead were less so, but all tended to inhibit both growth and antibiotic synthesis to a similar extent. Unexpectedly, manganese, cobalt, zinc, and, to a lesser extent, chromium caused complex effects that in general resulted in some enhancement of growth yield but a reduction in antibiotic titers. These complex effects meant that cobalt, manganese, and zinc had lower 50% inhibitory concentrations for antibiotic yields compared with those for biomass. The physiologically active divalent cations calcium and magnesium were also tested. Calcium at high concentrations was particularly effective in reducing antibiotic titers and enhancing growth yields. By adding calcium at different phases of growth, it could be demonstrated that it was most effective in reducing the antibiotic yield when added during the early growth phase. Addition during the antibiotic-producing phase resulted in little reduction of final actinorhodin titers.