An assessment of the basis of mercury tolerance inDunaliella tertiolecta

Abstract

The specific growth rate ofDunaliella tertiolectawas unaffected by mercury II concentrations of at least 2.03 μg at/1. At 10 μg at/1, it was eventually reduced by 84% but growth continued, giving a final level of cell material only 13% below that in a mercuryfree control. At this concentration, however, growth was largely uncoupled from division and giant cells were produced, probably due to the effect of mercury upon the production of methionine which is known to be implicated in the process of cell division.The basis of the mercury tolerance was investigated in terms of (1) mercury detoxication in the culture medium by complex or compound formation between the metal and metabolites produced by the cells, (2) the concentration of sulphydryl groups both within the cells as possible sequestration sites and in the cell membrane where any molecular disruption and permeability changes produced by the metal first occur, (3) the absence of cellular potassium leakage and (4) the resistance of the cell membrane to the uptake of mercury II ions. Where possible, the results were compared with those from determinations of the same properties of the mercury-sensitive speciesIsochrysis galbana. The experiments indicated that the mercury tolerance ofD. tertiolectais partly related to the slower rate of mercury accumulation by this species, but is largely due to the detoxication of the mercury within the cell possibly by the precipitation of a highly insoluble mercury compound