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Applied and Environmental Microbiology, January 2007, p. 243-249, Vol. 73, No. 1
0099-2240/07/$08.00+0     doi:10.1128/AEM.01794-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Biotransformation of Hg(II) by Cyanobacteria{triangledown} ,{dagger}

Daniel D. Lefebvre,* David Kelly, and Kenneth Budd

Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada

Received 28 July 2006/ Accepted 20 October 2006

The biotransformation of Hg(II) by cyanobacteria was investigated under aerobic and pH-controlled culture conditions. Mercury was supplied as HgCl2 in amounts emulating those found under heavily impacted environmental conditions where bioremediation would be appropriate. The analytical procedures used to measure mercury within the culture solution, including that in the cyanobacterial cells, used reduction under both acid and alkaline conditions in the presence of SnCl2. Acid reduction detected free Hg(II) ions and its complexes, whereas alkaline reduction revealed that meta-cinnabar (ß-HgS) constituted the major biotransformed and cellularly associated mercury pool. This was true for all investigated species of cyanobacteria: Limnothrix planctonica (Lemm.), Synechococcus leopoldiensis (Racib.) Komarek, and Phormidium limnetica (Lemm.). From the outset of mercury exposure, there was rapid synthesis of ß-HgS and Hg(0); however, the production rate for the latter decreased quickly. Inhibitory studies using dimethylfumarate and iodoacetamide to modify intra- and extracellular thiols, respectively, revealed that the former thiol pool was required for the conversion of Hg(II) into ß-HgS. In addition, increasing the temperature enhanced the amount of ß-HgS produced, with a concomitant decrease in Hg(0) volatilization. These findings suggest that in the environment, cyanobacteria at the air-water interface could act to convert substantial amounts of Hg(II) into ß-HgS. Furthermore, the efficiency of conversion into ß-HgS by cyanobacteria may lead to the development of applications in the bioremediation of mercury.

* Corresponding author. Mailing address: Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada. Phone: (613) 533 6141. Fax: (613) 533 6617. E-mail: lefebvre{at}biology.queensu.ca.

{triangledown} Published ahead of print on 27 October 2006.

{dagger} This paper is dedicated to the memory of K. Budd.

Applied and Environmental Microbiology, January 2007, p. 243-249, Vol. 73, No. 1
0099-2240/07/$08.00+0     doi:10.1128/AEM.01794-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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