Effect of Metallic Cations on the Viability of Phenol-treated Escherichia coli

Five metallic cations (Fe3+ , Cr3+ , Ca2+ , Mg2+ , Mn2+ ; concentration range, 1.85 10-4 to 37 10-4 m ) were incorporated individually as chlorides into nutrient broth and agar media used for the recovery of phenol-treatedEscherichia coli . The effects observed varied with the concentration and the ionic species. In nutrient agar, Fe3+ and Cr3+ were generally beneficial but were toxic at 37 10-4 m . Of the divalent ions tested, Ca2+ and Mg2+ usually gave higher counts in nutrient broth, except at a concentration of 9.25 10-4 m , whereas the effect of Mn2+ was rather variable. Two possible explanations are suggested to explain these effects. Toxic materials may be removed from the media by the precipitates formed on the addition of Fe3+ or Cr3+ , or, in the case of the divalent ions, the integrity of the bacterial cell membranes may be maintained.