Dr. Weeks’ Comment: Mercury is a neurotoxin. No doubt or debate about that scientific fact. But toxicity is relative “depends upon the dose” (per Paracelsus) and the tolerance of the subject. What intoxicates me may not bother you (in the short term). Now we learn about certain genetic factors which predispose to risk of mercury intoxication.
Scientists Solve Mercury Mystery, Taking Big Step Toward Protecting Human Health
Feb. 7, 2013 — By identifying two genes required for transforming inorganic into organic mercury, which is far more toxic, scientists have just taken a significant step toward protecting human health.
The question of how methylmercury, an organic form of mercury, is produced by natural processes in the environment has stumped scientists for decades, but a team led by researchers at Oak Ridge National Laboratory has solved the puzzle. Results of the study, published in the journal Science, provide the genetic basis for this process, known as microbial mercury methylation, and have far-reaching implications.
“Until now, we did not know how the bacteria convert mercury from natural and industrial processes into methylmercury,” said ORNL’s Liyuan Liang, a co-author and leader of a large Department of Energy-funded mercury research program that includes researchers from the University of Missouri-Columbia and University of Tennessee.
“This newly gained knowledge will allow scientists to study proteins responsible for the conversion process and learn what controls the activity,” said Liang, adding that it may lead to ways of limiting methylmercury production in the environment.
For some 40 years scientists have known that when mercury is released into the environment certain bacteria can transform it into highly toxic methylmercury. Exactly how bacteria make this happen has eluded scientists. The challenge was to find proteins that can transfer a certain type of methyl group and to identify the genes responsible for their production.
Ultimately, by combining chemical principles and genome sequences, the team identified two genes, which they named hgcA and hgcB. Researchers experimentally deleted these genes one at a time from two strains of bacteria, which caused the resulting mutants to lose the ability to produce methylmercury. Reinserting these genes restored that capability, thus verifying the discovery.
The researchers found that this two-gene cluster is present in all known mercury-methylating bacteria, and they predicted that more than 50 other microorganisms may methylate mercury because they have a pair of similar genes.
- Jerry M. Parks, Alexander Johs, Mircea Podar, Romain Bridou, Richard A. Hurt, Steven D. Smith, Stephen J. Tomanicek, Yun Qian, Steven D. Brown, Craig C. Brandt, Anthony V. Palumbo, Jeremy C. Smith, Judy D. Wall, Dwayne A. Elias, and Liyuan Liang. The Genetic Basis for Bacterial Mercury Methylation. Science, 7 February 2013 DOI: 10.1126/science.1230667