Influence of cadmium ions on Streptomyces strains

The sensitivity of 19 strains of Streptomyces to cadmium ions was studied by the disk method using cadmium chloride in quantities: 2, 5, 10 ug Cd2+. Sensitivity was estimated by measuring the size of zones of the growth inhibition. Also four selected strains were spread on substrates containing 1, 5, 10 ppm Cd2+ and the number of colonies was countwed. In all tests a comparison was made between the 2 kinds of inoculum: spores suspended in physiological salt solution and spores prior preincubation on a medium. Differences of the reaction to cadmium ions among tested strains were observed. Spores after germination were more resistant to cadmium ions than non-germinating spores of the same strain. Five ppm Cd2+ added to the medium decreased the number of colonies, especially in the case of sensitive strains. Ten ppm of cadmium ions decreased the number of colonies of the resistant strains and inhibited the growth of sensitive strains.