Led by Caitlin Gionfriddo and Dr. John Moreau from the University of Melbourne, an international team of scientists from the Center for Systems Genomics at the University of Melbourne, the US Geological Survey, and Lawrence Livermore National Laboratory, have become the first to find that sea ice bacteria can change mercury into methylmercury.
When ingested, methylmercury can travel to the brain, causing developmental and physical problems in fetuses, infants and children. Being much more toxic than mercury, which is also poisonous. Seafood contaminated with methylmercury has been known to cause mercury poisoning in humans.
Methylmercury builds up in the food web through a process called ‘biomagnification’, said Gionfriddo, a PhD candidate from the School of Earth Sciences, University of Melbourne. “Larger fish eat smaller contaminated fish, and continuously accumulate methylmercury at harmful levels for human consumption.”
In order to find out how methylmercury enters the marine environment and eventually ends up in the food we eat, Science Daily reports that Gionfriddo spent two months on board the icebreaker Aurora Australis, collecting samples of Antarctic sea ice during an expedition with the Australian Antarctic Division.
After collection, the sea ice samples were analysed for different forms of mercury by the US Geological Survey, while DNA and proteins from sea ice microorganisms were studied at the University of Melbourne and the Lawrence Livermore National Lab.
Using metagenomic analysis of whole-community microbial DNA from Antarctic snow, brine, sea ice and sea water, the research team confirmed the presence of bacteria in the sea ice with the genetic ability to convert mercury into its more toxic form, methylmercury.
“These results are the first to identify a particular genus of bacteria, a marine microaerophilic bacterium called Nitrospina, as capable of producing methylmercury in Antarctic ice,” Dr. John Moreau said. Especially interesting was the absence of any anaerobic bacteria known to methylate mercury in the samples studied.
Also of interest is a study reported on by Digital Journal in September 2015. In this study, methylmercury accumulations in Arctic seawater were studied. The research found that climate-driven stratification of water columns in margin areas with sea-ice melt created a layer of “marine snow” that becomes a feeding zone for plankton.
The bacteria in this zone are all the while performing a complex chemical process, turning naturally occurring mercury into methylmercury, a deadly neurotoxin. This is how the accumulated methylmercury moved on up the food chain. In the study, published in the journal PNAS, there was no indication as to what kind of bacteria was involved.
This interesting study, “Microbial mercury methylation in Antarctic sea ice,” was published in the journal Nature Microbiology on August 1, 2016.
