Methylmercury formation in coastal seas: understanding risks associated with permanent and temporary oxygen deficiency
The aim of the project is to describe mechanistic principles for methylmercury formation in brackish and marine coastal seas with permanent and temporary oxygen deficiency. Specifically, we will test the hypothesis that methylmercury formation rate and amount can be predicted by the gene expression of the gene cluster hgcAB and the availability for methylation of mercury. The studies will be carried out in the Baltic Sea and Norwegian fjords.
Mercury is classified by the World Health Organization as one of the ten chemicals that pose the greatest threat to global public health. The problems with mercury are mainly caused by methylmercury, which is neurotoxic and enriched in aquatic biota. Oxygen deficiency is increasing in coastal seas and the global ocean and is one of the most serious environmental changes caused by human impact.
Methylmercury is mainly formed by anaerobic microorganisms in oxygen deficient environments by methylation of inorganic mercury via two enzymes encoded by the gene pair hgcAB. Increased oxygen deficiency can potentially lead to increased formation of methylmercury, which can pose a threat to fisheries as an ecosystem service in many areas. However, our understanding of the mechanisms and limiting factors for methylmercury formation under such conditions is insufficient.
The overall objective of the research is to describe mechanistic principles for methylmercury formation in brackish and marine coastal environments with permanent and temporary oxygen deficiency. Our research team combines key competencies in biogeochemistry and molecular biology and we will use newly developed methods to clarify these unanswered and important issues. We will characterize the composition and function of microorganisms that carry the hgcAB genes in the different environments and clarify how the gene expression of hgcAB in specific microorganisms is related to key environmental variables. We will also study how chemical forms of mercury and the availability for methylation are governed by environmental variables. Furthermore, we will clarify whether the formation of methylmercury can be predicted by the expression of hgcAB by specific microbes and by the availability of mercury for methylation.
We will carry out the studies in the Baltic Sea and Norwegian fjords and link our studies to projects that study genes related to mercury transformations on a global level. Through this synergy, we will describe mechanistic principles and develop a general predictive model for methylmercury formation and scale these up to a global level. The project's main societal benefit is to provide knowledge that is crucial for predicting how marine food webs and humans will be exposed to methylmercury as a result of increased oxygen deficiency in seas and the ocean.