SUMMARY: A turbidimetric assay is described for antibiotic substances produced by , NCIB 8132, and , NCIB 4940, based on the amount of inhibition of growth of a celluloseless mutant. Yield of antibiotic from each organism was independent of the source of nitrogen in the medium, but varied markedly with the carbon source and was highest when the organisms were grown for 10 days at 30° in a medium containing glucose (9%, w/v), Difco yeast-extract (0·5%, w/v) and peptone (Evans, 3%, w/v), in distilled water. Under these conditions growth of the assay organism was inhibited 50% by filtrate diluted 1/44. The antibiotics were extremely alkali-labile being destroyed at 18° in 2 min. at pH 10. Activity of the filtrate from organism NCIB 8132 was not affected significantly by treatment with calcium carbonate, charcoal, cation- or anion-exchange resins, but was decreased by extraction at pH 3·0 with -butanol, chloroform or methyl ethyl ketone. Activity of filtrate of organism NCIB 4940 was decreased by treatment with charcoal, cation- or anion-exchange resins and by extraction at pH 3·0 with benzene, -butanol, chloroform, diethyl ether, ethyl acetate or methyl ethyl ketone.


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