A comparison of methods for removing trace metals from microbiological

SUMMARY: Thirty-eight methods or modifications of methods for removing trace metals from nutrient media were tested, using Aspergillus niger as test organism to indicate deficiencies. The most marked symptoms of Zn and Fe deficiencies were obtained after treatment by the M 2 0 3 or dithizone + oxine methods, of Cu and Rln deficiencies by the A1,03 method, and of Mo deficiency by Nicholas’s method which involves co-precipitation with sulphides of Cu and Pb. Four strains of A. niger differed in their trace element requirements. Shake cultures of A. niger gave less growth in complete medium than did surface cultures, while in deficient media this was reversed. Sucrose peptone and broth media were only partially purified by the A120, treatment. Deficiencies of Fe, Zn and Cu were obtained for Chlorella vulgaris, and o f Fe and Zn for Torulopsis utitis, as detected by growth response. Apart from decrease of growth, trace metal deficiency symptonis in Penicillium roqueforti were not very obvious. This paper summarizes work undertaken to compare the relative merits of most known methods for removing Fe, Zn, Cu, Mn and Mo from culture media, including methods and modifications devised by the present authors. Foster (1949) outlined many methods for freeing media from trace metal;, without deciding which are the most efficient. Steinberg (1950) compared the relative merits of a number of techniques, only to find that his method, devised in 1919, which uses CaCO, as an adsorbent, was superior to many advocated more recently. The various methods available can be divided into two broad groups: ( a) those which employ a solid such as charcoal or CaCO, for adsorbing trace elements, the solid adsorbent being subsequently removed by filtration; ( b) those which employ chelating agents such as diphenylthiocarbazone (dithizone) or 8-hydroxyquinoline (oxine), which combine with metals to form water-insoluble complexes that can be removed by extraction with organic solvents such as ether or carbon tetrachloride. In a few methods, both techniques are combined