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 HgCl(2) 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) approximately 20 min). This thermophile was also able to generate Hg(0) even after all exogenously applied HgCl(2) had been biotransformed. The results suggest that beta-HgS may be the major dietary mercurial for grazers of contaminated eukaryotic algae.