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Mechanistic principles of methylmercury formation in anaerobe microbial biofilms

Research project is financed by the Swedish Research Council.

The aim of the project is to formulate mechanistic principles for methylmercury formation in microbial biofilms to advance the ability to understand and predict this critical process in the environment.

Head of project

Project overview

Project period:

2022-01-01 2025-12-31

Participating departments and units at Umeå University

Department of Chemistry

Research area

Chemical sciences, Environmental chemistry, Marine science

External funding

Swedish Research Council

Project description

We will (1) identify how the chemistry of the biofilm matrix controls Hg cellular uptake, (2) determine if methylmercury formation rate is limited by uptake, expression of methylation genes or biofilm cell metabolic status and (3) study metabolic pathways for methylmercury formation. By using biofilms, the derived mechanistic framework will be more relevant to natural conditions and a major step towards predicting methylmercury formation in the environment. It will also provide a new basis for developing mechanistic models for both scientific and societal use to mitigate the adverse environmental and health effects of methylmercury.

The spread of mercury in aquatic and terrestrial ecosystems poses significant threats to wildlife, human health and the socio-economy. Mercury is classified by the WHO as one of ten chemicals that pose the greatest threat to global public health. In Sweden, the limit value for mercury in fish is exceeded in thousands of lakes and mercury is the main reason for recommendations on limiting fish consumption from, among others, Swedish and American EPA and FDA. These major problems with mercury arise mainly as a result of the formation of methylmercury, a highly neurotoxic form of mercury that is bioaccumulated in aquatic biota and in certain plants. Methylmercury is formed intracellularly in specific types of anaerobic microorganisms by methylation of inorganic mercury. Despite extensive basic research, attempts to generate predictive models for the formation of methylmercury in the environment have not been successful. This inability limits our fundamental understanding of mercury biogeochemical cycling and our ability to predict how biota and humans are exposed to methylmercury. This compromises reliable risk assessments and scientifically based measures to mitigate high levels of mercury.

Mechanistic studies of methylmercury formation have been done almost exclusively on free-living (so-called planktonic) bacteria, while bacteria in the environment predominantly occur as aggregated communities, so-called biofilms. Laboratory experiments have shown ten times higher rate of formation of methylmercury in biofilms compared to planktonic cells, but the reasons are unclear and there are no mechanistic studies of biofilm systems. This lack is a "blind spot" in our understanding of methylmercury formation in the environment.

The overall purpose of the research project is to formulate mechanistic principles for the formation of methylmercury in microbial biofilms to advance the ability to understand and predict this critical process in the environment. We will (1) identify how the chemical composition of the "film" surrounding biofilms controls cellular uptake of mercury, (2) clarify whether the rate of methylmercury formation is limited by cellular uptake, expression of specific genes leading to mercury methylation or metabolic status of biofilm cells , and (3) identify metabolic pathways that lead to mercury methylation in biofilms.

Our research team constitutes a strong combination of expertise and methods for mechanistic studies of microbial methylmercury formation and molecular studies of biofilms. We will address the challenging objectives of the project through a combination of new methods and experimental strategies, based on advanced spectroscopic techniques. By studying biofilms, the mechanistic framework will be more relevant to natural conditions and an important step towards predicting methylmercury formation in the environment. Our hope is that the mechanical framework will ultimately provide an improved basis for the development of mechanistic models for both scientific and societal use to counteract the negative environmental and health effects of methylmercury.

External funding