ENHANCED HEAVY-METAL TOLERANCE IN 2 STRAINS OF PHOTOSYNTHETIC EUGLENA-GRACILIS BY PREEXPOSURE TO MERCURY OR CADMIUM

The effects of different concentrations of Hg, Cd, and Pb on cell grow th, oxygen consumption, and production and contents of chlorophyll a a nd b of Z and B strains of Euglena gracilis was studied. Cell uptake o f Cd and Pb was also determined, A,greater cell density reached in the presence of Cd2+ correlated with a lower metal uptake capacity in B-s train cells, Cells of Z strain, preexposed to low concentrations of ei ther Hg2+ (1.5 mu M) or Cd2+ (50 mu M) for several generations showed improved heavy metal tolerance (greater cell density and viability) to gether with similar metal uptake capacity. Because Cd2+ preadaptation but not Hg2+ pretreatment induced a significant increase in the conten t of acid-soluble thiols, the data suggest the existence of different mechanisms of heavy metal detoxification in Euglena. The fact that Z-s train cells showed a greater Cd2+ uptake under all tile conditions ass ayed suggests that Z strain would be more suitable for bioremediation of polluted waters.