Makayla Harrison

Concordia University
Linking mercury methylation to microbial community structure and diversity along the St. Maurice River in Québec, Canada

M. C. Harrison, M. Leclerc, D. E. Ponton, M. Amyot, A. J. Poulain, D. A. Walsh

Mercury is a heavy element that occurs in aquatic environments through both natural and anthropogenic deposition. When mercury undergoes methylation, it is transformed into methylmercury, a neurotoxin capable of bioaccumulating in food webs. Methylation is facilitated through methylating microorganisms, all of which contain a hgcAB gene pair. High levels of methylmercury have been recorded near run-of-river hydroelectric dams in Québec. Although typically thought to occur in sediments, mercury methylation was recently shown to also occur in freshwater periphyton. Using periphyton samples, 16S rRNA and hgcAB genes targeting bacteria, and mcrA genes targeting methanogenic archaea, were used to assess the natural diversity of mercury methylating microorganisms, compare the microbial community composition between sites, and quantify the abundance of methylating microorganisms. 16S rRNA gene analysis revealed lineages associated with mercury methylating microorganisms being present at all sites. Further metagenomic analyses using the hgcAB and mcrA gene will identify specific microorganisms responsible for the methylation of mercury. As periphyton is at the bottom of the food web, understanding mercury methylation in periphyton is important to prevent further bioaccumulation in higher trophic levels.