A New Channel-forming Antibiotic from Streptomyces coelicolor A3(2) Which Requires Calcium for its Activity

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Abstract
A recently discovered antibiotic (CDA; calcium-dependent antibiotic) of S. coelicolor A3(2) was effective against a wide range of gram-positive bacteria only in the presence of Ca2+. Producer and non-producer strains were identified and several media tested for their ability to support antibiotic production. The action of Ca2+ was not simulated by any other cations tested. The antibiotic induced discrete conductance fluctuations in planar lipid bilayer consistent with a channel-forming action. The electrical potential difference caused by a concentration difference of various salts across the CDA-containing bilayer showed the channel to be cation-selective but of a size that discriminated against tetramethyl ammonium and choline ions. Thus, the antibiotic activity of CDA is due to tis action as a Ca2+-dependent ionophore.