Mercury, as well as other heavy metals, is enriched in geothermal environments, such as deep ocean hydrothermal vents and volcanic springs, where it can reach concentrations that are considered toxic to living organisms. Microorganisms living in these environments have evolved in the presence of mercury for extended periods of time and therefore the evolutionary origin of microbial resistance and transformations of mercury might be found in geothermal environments. We are looking for mercury resistant microorganisms that we isolated from such environments. The figure below shows some of the sites where we collect samples.

 

We have special interest in studying the interactions of mercury with chemosynthetic sulfur oxidizing bacteria. They are major players in deep sea vents in which reduced sulfur compounds emitted with the hot water (see Figure below) are the primary source of energy, and the activity of autotrophic organisms produce the carbon source necessary to sustain life. Eukaryotic organisms such as the tubeworms, Riftia (see figure below) have symbiotic sulfur oxidizing bacteria that provide them with nutrients and energy that allow them to flourish in deep sea vents, miles below the ocean surface away from any light source.

Results to date suggest that concentrations of Hg in deep-sea hydrothermal fluids are elevated, and that mercury resistant microbes are enriched in geothermal environments. The abundance of these organisms in deep-sea geothermal environments varies from 0.9 to 14% of the total chemosynthetic thiosulfate oxidizer community and all isolates of thiosulfate oxidizing bacteria from Mount Amiata were resistant to µM concentrations of mercuric chloride. These results suggest microbial adaptation to mercury. Click here if you would like to learn more about results of our research in deep sea vents. (Vetriani et al., 2005)

This study is performed by Melitza Crespo-Medina, a graduate student in the Molecular Microbiology and Genetics Program who is isolating, enumerating, and characterizing mercury resistant chemosynthetic organisms form deep-sea hydrothermal vents. Research in progress with samples collected in Yellowstone National Park is performed by Pat Lu Irving in our lab who is enriching and isolating pure cultures of mercury resistant microbes and Yanping Wang who is performing a culture independent studies of merA genes. Our research on mercury impacted geothermal environments is a collaboration with Dr. Costantino Vetriani from our department.