Mercury uptake and removal by Euglena gracilis

The uptake and removal of mercury (added as HgCl2) from the culture medium by Euglena gracilis was studied. In cultures initiated in the light, cells accumulated a small fraction of the added heavy metal (5-13%). Mercury was both biologically and nonbiologically volatilized, and cell growth was partially inhibited; under these conditions the glutathione content was 3.2 nmol/10(6) cells. In contrast, in cultures initiated in the dark, mercury uptake by cells was two to three times higher, biological volatilization remained unchanged and nonbiological volatilization and growth were negligible; the glutathione content diminished to 1.4 nmol/10(6) cells. Biological mercury volatilization depended on cell density and metal concentration, but was light-independent. Thus, volatilization of mercury by Euglena appeared not to be an effective mechanism of resistance, whereas a high intracellular level of glutathione and a low mercury uptake seemed necessary for successful tolerance.