EXTREME TOLERANCE TO CADMIUM AND HIGH-RESISTANCE TO COPPER, NICKEL AND ZINC IN DIFFERENT ACIDIPHILIUM STRAINS

Acidiphilium symbioticum strains exhibited extremely high tolerance to CdSO4, growing at a concentration of 700 mmol l(-1) or more in MGY me dium (g l(-1) composition: KCl, 0.1; MgS0(4).7H(2)O, 0.25; (NH4)(2)SO4 , 2.0; K2HPO4, 0.25; glucose, 1.0; yeast extract, 0.1) of pH 3. Fairly high concentrations of ZnSO4 (200 >125 mmol l(-1)), NiSO4 (50 >20 mmo l l(-1)) and CuSO4 (25 >15 mmol l(-1)) were also tolerated by these st rains. Acidiphilium multivorum grew in the presence of NISO4 (400 >350 mmol l(-1)), ZnSO4 (50 >40 mmol l(-1)), CdSO4 (40 >20 mmol l(-1)) and CuSO4 (20 >10 mmol l(-1)) while an Acidiphilium strain GS18h tolerate d ZnSO4 (100 >60 mmol l(-1)), NiSO4 (50 >30 mmol l(-1)), CuSO4 (30 >15 mmol l(-1)) and CdSO4 (20 >10 mmol l(-1)) in the same medium. Acidiph ilium angustum, on the other hand, was found to be metal sensitive-gro wth inhibition being observed at concentrations of 10 mmol l(-1) ZnSO4 , 10 mmol l(-1) CuSO4, 20 mmol l(-1) NiSO4 and 0.2 mmol l(-1) CdSO4 in MGY medium. Acidiphilium organovorum also exhibited tolerance to thes e metal sulphates in this medium at the levels of 70 >60 mmol l(-1) fo r Zn, 20 >10 mmol l(-1) for Cd and Ni, and 10 >5 mmol l(-1) for Cu. Th is strain, interestingly enough, showed a much higher level of toleran ce in MAGY medium (g l(-1) composition: KCl, 0.15; MgSO4.7H(2)O, 3.36; K2HPO4, 0.15; (NH4)(2)SO4, 0.15; Al-2(SO4)(3).18H(2)O, 2.25; CaCl2.2H (2)O, 0.97; MnSO4.H2O, 0.12; glucose, 1.0; yeast extract, 0.1) of pH 3 than in MGY medium. Replacement of carbon source, however, did not af fect the tolerance levels to any great extent.