Microbial methylation of mercury in the North Harbour of Lake Superior

Abstract

Mercury is a known contaminant in the North Harbour of Lake Superior due to the decommissioned “Thunder Bay Fine Papers” pulp and paper mill. The cause for concern for organisms in the lake and for humans occurs when mercury undergoes a transformation to methylmercury (MeHg). Methylmercury is a neurotoxin that has the ability of bioaccumulation and biomagnification- making it a primary concern for human health. The methylation of mercury can occur by a variety of mechanisms, including both biotic and abiotic, however methylation via microorganisms is considered the primary mechanism in most aquatic systems. Microorganisms that can carry out this reaction do so to lessen the toxic effects of mercury on themselves. There are several known microbes that will methylate mercury, such as sulfate reducing bacteria, however the diversity of microorganisms that can carry out this reaction goes beyond what researchers currently know. Recent studies have identified a gene correlated to methylation known as the hgcAB gene cluster. This research aims to answer two main questions: 1) are mercury-methylating microorganisms present in sediment samples from the North Harbour and if so, 2) which microorganisms are present? Amplification of the hgcA gene by PCR shows that the gene is present in sediment samples from the North Harbour. Sequencing experiments were inconclusive, and the identities of the microorganisms that contain the hgcA gene are unknown at this time.