. The actinomycetes. Actinomycetales. 144 THE ACTINOMYCETES, Vol. I replaced by zinc or iron. Growth of S. scabies was inhibited by ahuninum ions in concen- trations of 20 or more parts per million (Gries). This inhibition could not be reversed by the addition of magnesium. The addition of metals to the medium also influences greatly pigment production. This is true of ferroverdin, a green iron- containing pigment produced by a strepto- myces. Zinc sulfate concentrations of per cent increase the rate of pigment forma- tion in strains of red-yellow-pigment-forming streptomycetes (Chain et
. The actinomycetes. Actinomycetales. 144 THE ACTINOMYCETES, Vol. I replaced by zinc or iron. Growth of S. scabies was inhibited by ahuninum ions in concen- trations of 20 or more parts per million (Gries). This inhibition could not be reversed by the addition of magnesium. The addition of metals to the medium also influences greatly pigment production. This is true of ferroverdin, a green iron- containing pigment produced by a strepto- myces. Zinc sulfate concentrations of per cent increase the rate of pigment forma- tion in strains of red-yellow-pigment-forming streptomycetes (Chain et al.). Omission of magnesium or calcium from the medium re- duced the amount of diffusible pigment but omission of zinc or iron did not have any effect on pigment production by S. fradiae (Mohan). Stapp and Spicher and Spicher observed that soil extract, or ash of soil extract, added to synthetic nutrient solutions, gave in- creased growth of a group of streptomycetes (Fig. 68). The increase in growth was nearly proportional to the amount of ash added. The media were purified by various proce- dures, including sulfide precipitation and use of calcium carbonate and 8-hydroxyquino- line. When added to the medium in certain concentrations and combinations, various metals also yielded increased growth over metal-deficient controls. The most effective metals and concentrations were: iron at mg per 100, manganese at mg per 100, and zinc, copper, and molybdenum at mg per 100. Combinations were more effective than single additions, the most effective being iron-zinc, iron-manganese- zinc, and iron-manganese-zinc-molybdenum (Fig. 69). Heim and Lechevalier used a chemically defined medium made metal-deficient by treatment with activated chromatographic alumina. The effect of iron, zinc, manganese and calcium on the growth of eight strepto 60 §40 20 5 /' J ^^ r\ i^^^^ ^^0^"^. 8 10 0 2 4 6 DAYS Figure 69. Effect on streptomyces mycelial growth produced by various so
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