Biotransformation of mercury in pH-stat cultures of eukaryotic freshwater algae

Eukaryotic algae were studied to determine their ability to biotransform Hg-II under aerated and pH controlled conditions. All algae converted Hg-II into beta-HgS and Hg-0 to varying degrees. When Hg-II was administered as HgCl2 to the algae, biotransformation by species of Chlorophyceae (Selenastrum minutum and Chlorella fusca var. fusca) was initiated with beta-HgS synthesis (K (1/2) of hours) and concomitant Hg degrees evolution occurred in the first hour. Hg degrees synthesis was impeded by the formation of beta-HgS and this inhibition was released in C. fusca var. fusca when cellular thiols were oxidized by the addition of dimethylfumarate (DMF). The diatom, Navicula pelliculosa (Bacillariophyceae), converted a substantially greater proportion of the applied Hg-II into Hg-0, whereas the thermophilic alga, Galdieria sulphuraria (Cyanidiophyceae), rapidly biotransformed as much as 90% of applied Hg-II into beta-HgS (K (1/2) approximate to 20 min). This thermophile was also able to generate Hg-0 even after all exogenously applied HgCl2 had been biotransformed. The results suggest that beta-HgS may be the major dietary mercurial for grazers of contaminated eukaryotic algae.