Effect of trace elements on the production of pigments by a pseudomonad

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Abstract
The effect of different trace-element ions on the production of pigments (particularly a pteridine derivative) by a pseudomonad was studied in media free from contaminating metal ions. Magnesium ions which were essential for pigment formation and growth of the organism were irreplaceable by any of the other metal ions tested. Ferrous ions which stimulated pigment formation at low concentrations, were inhibitory at higher concentrations. Manganese ions were stimulatory at all concentrations tested; but Zn2 , Cu2+ and Ni2+ ions, though stimulatory at lower concentration, inhibited pigment formation at higher concentrations. Cobalt ions were inhibitory at all concentrations. Borate was without any effect, whereas dichromate and molybdate were inhibitory at higher concentrations.