Investigations on organic fungicides: XI. The Role of metals and chelating agents in the fungitoxic action of sodium dimethyldithiocarbamate (NaDDC)

Abstract

1. 1. The role of metals and chelating agents in the fungitoxic action of sodium dimethyldithiocarbamate (NaDDC) has been studied using Aspergillus niger as a test mould. 2. 2. In liquid glucose mineral salts medium containing only traces of heavy metals NaDDC does not produce a “first zone of inhibition”. Addition of Cu or Co to these media does, however induce this zone. Fe, Zn and Mn are unable to bring about the same effect. 3. 3. On agar media the amount of Cu required to induce a first zone of inhibition for A. niger has been found to be far less than in liquid media. 4. 4. Comparison of spectrophotometric measurements and growth results in liquid medium has revealed that the “first zone of inhibition” coincides with the presence of the 1:1 complex of copper and dithiocarbamate. The zone of inversion growth emerges at higher NaDDC concentrations when the 1:2 complex is present instead of the toxic 1:1 complex. These results support those of Goksøyr found for Saccharomyces cerevisiae. The second zone of inhibition is related to the presence of free dithiocarbamate. 5. 5. The toxic action of the 1:1 complex must be ascribed to combination with an essential enzyme. 6. 6. The antagonistic activity of imidazole derivatives cannot be due to removal of Cu from the 1:1 complex. These compounds are, however, supposed to protect an essential enzyme by competing with it for the toxic 1:1 complex. 7. 7. The free dithiocarbamate induces the mould to accumulate pyruvic acid; the 1:1 complex seems to do so also, but to a far lesser extent.