Transformations of inorganic mercury by Candida albicans and Saccharomyces cerevisiae

Saccharomyces cerevisiae and Candida albicans were incubated with 0.25, 0.5, or 0.75 micrograms of Hg (as HgCl2) per ml of Nelson's medium in the presence of trace amounts of oxygen at 28 degrees C for 12 days. Two control media were used, one without added Hg and one without yeast inoculum. Yeast cell growth was estimated after 1, 2, 3, and 8 days of incubation. The contents of organomercury in the system and of elemental mercury released from the media and collected in traps were determined at the end of the experiments. The results were as follows. (i) C. albicans was the more mercury-resistant species, but both yeast species failed to grow in the media containing 0.75 micrograms of Hg per ml. (ii) The amounts of organomercury produced by the two species were proportional to the amount of HgCl2 added to the medium. In all cases C. albicans produced considerably larger amounts of methylmercury than S. cerevisiae. (iii) The amounts of elemental Hg produced were inversely proportional to the HgCl2 level added in the case of S. cerevisiae but were all similar in the case of C. albicans. (iv) Neither organomercury nor elemental Hg was produced in any of the control media.