Microbes living in rivers, lakes, and oceans take a form of mercury and convert it into methylmercury (CH₃Hg+). Methylmercury is consumed by fish and shellfish and is bioaccumulative. A research team led by the U.S. Department of Energy's Oak Ridge National Laboratory has recently achieved major new insights into the mechanism of microbial "mercury methylation" by identifying two key genes in microbes that are responsible for this process. This could open the way to advances in detection and remediation of environmental mercury contamination. The work also illustrates how the new tools and methods of contemporary "systems biology" are enabling researchers to penetrate biological mysteries that have eluded previous generations of investigators.