07/15/2016

Molecular Probes Developed for Mercury Methylating Genes

The new tools will enable researchers to more quickly detect and quantify microbes with these genes in the environment.

The Science

Researchers have developed deoxyribonucleic acid (DNA) and messenger ribonucleic acid (mRNA) probes to not only identify microbes that carry the genes for mercury (Hg) methylation, but also to quantify the extent to which specific types of microbes contribute to the methylation process.

The Impact

The neurotoxin methylmercury (MeHg) poses a serious risk to human health. MeHg production in nature is associated with anaerobic microbes. The development of DNA and mRNA probes represents a substantial improvement over previous work to develop both qualitative and quantitative primers for Hg-methylating genes. These new primers take into consideration the different degrees of methylation potential for specific types of microbes, which ranges from ~10% in the Archaea to ~90% in some Deltaproteobacterial species. These findings will enable a more realistic understanding of possible MeHg generation levels that may occur in a given environment, with the resulting data enabling more accurate risk management assessments.

Summary

Two genes, hgcA and hgcB, are essential for microbial Hg methylation. Detecting and estimating their abundance in microbes in conjunction with quantifying Hg species and other geochemical factors is critical in determining potential hotspots of MeHg generation in at-risk environments. Scientists at Oak Ridge National Laboratory led a team that identified a broad range of degenerate polymerase chain reaction (PCR) primers spanning known hgcAB genes to determine the presence of both genes in diverse environments. These broad-range primers were tested against an extensive set of pure cultures with published genomes that are known to methylate mercury, including 13 Deltaproteobacteria, nine Firmicutes, and nine methanogenic Archaea. For all these types of microbes, the primers not only consistently identified the methylating genes, but they enabled the team to quantify the extent to which each type of microbe methylates Hg. Environmental samples were further used to validate the primers and determine corrective calculations for DNA extraction and PCR amplification efficiencies. Taken together, these findings will enable a more realistic picture of possible MeHg generation levels that may occur in a given environment.

Principal Investigator(s)

Dwayne Elias Dwayne Elias
Oak Ridge National Laboratory
eliasda@ornl.gov

Funding

This research was funded by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science, as part of the Mercury Science Focus Area project at Oak Ridge National Laboratory.

References

G. A. Christensen, A. M. Wymore, A. J. King, M. Podar, R. A. Hurt Jr., E. U. Santillan, A. Soren, C. C. Brandt, S. D. Brown, A. V. Palumbo, J. D. Wall, C. C. Gilmour, and D. A. Elias, “Development and validation of broad-range qualitative and clade-specific quantitative molecular probes for assessing mercury methylation in the environment.” Applied and Environmental Microbiology (2016). DOI:10.1128/ AEM.01271-16.