“LIESEGANG-LIKE” RINGS OF GROWTH AND INHIBITION OF BACTERIA IN AGAR CAUSED BY METAL IONS AND CHELATING AGENTS,

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Abstract
Multiple alternate rings of growth and inhibition of growth of microorganisms on agar medium are produced by placing chelating agents in the medium and salts in filter paper discs on the surface of the medium, or vice versa, and allowing the materials in the discs to diffuse into the agar. As many as 6 alternate and concentric rings of growth and inhibition occur around discs when the dishes are incubated. Of the chelating agents tested, 5-methyl-l,10-phenanthroline and 8-hydroxyquinoline give the best formation of multiple rings with Micrococcus pyogenes var. albus and Bacillus subtilis as the test organisms. Comparison of these rings with the Liesegang rings, caused by interactions of salts in semi-solid phases such as gelatin or agar colloids, suggests that they both may be caused by the same phenomenon. The rings of growth and inhibition apparently result from concentric areas, or "gradient zones," of different mixtures of free chelating agent, metal chelate complexes and free metal ions.