Streptomyces rishiriensis produces at least five closely related antibiotics. Strain selection yielded a culture producing only the most active component, coumermycin A. Hydrolysis of this antibiotic by barium hydroxide yielded both 5-methyl-pyrrole-2-carboxylic acid and pyrrole-2-carboxylic acid, which could be separated by paper chromatography. Coumermycin A was thus shown to be two fractions, designated A(1) and A(2) depending upon the nature of the pyrrole carboxylic acid portion. The addition of cobalt to the fermentation medium at a level as low as 0.01 mug/ml shifted the fermentation exclusively to the production of coumermycin A(1). Other ions were ineffective, except nickel, whose activity could be explained by the presence of contaminating cobalt.
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Claridge et al. (1966) studied this question.