Extracellular Polymeric Substances Stop Migration of Subsurface Contaminants
Subsurface uranium is a significant contaminant at U.S. Department of Energy sites. Remediation solutions include immobilizing contaminants to prevent them from reaching groundwater. Using a model organism isolated from a uranium seep of the Columbia River, scientists recently quantified how extracellular polymeric substances (EPS) in subsurface environments can be used to immobilize heavy metal and radionuclide contaminants such as uranium [U(VI)]. In geologic systems, EPS can help bind microbes to mineral surfaces, influence cellular metabolism, and influence the fate and transport of contaminants. Using a novel biofuel reactor designed by scientists from the Environmental Molecular Sciences Laboratory (EMSL), the team prepared biofilms of a Shewanella species that produces EPS, and quantitatively analyzed the contribution of EPS to U(VI) immobilization. Using EMSL’s nuclear magnetic resonance capabilities to analyze chemical residues in EPS samples and cryogenic fluorescence spectroscopy to obtain sensitive U(VI) measurements, they tested the reactivity of loosely associated EPS and bound EPS with U(VI). The scientists found that, when reduced, the isolated cell-free EPS fractions could reduce U(VI) and the bound EPS contributed significantly to its immobilization, primarily through redox-active proteins. For loosely associated EPS, sorption of U(VI) was attributed predominantly to reaction with polysaccharides. These results could lead to the development of improved remediation techniques for subsurface contaminants.
Cao, B., B. Ahmed, D. W. Kennedy, Z. Wang, L. Shi, M. J. Marshall, J. K. Fredrickson, N. G. Isern, P. D. Majors, and H. Beyenal. 2011. “Contribution of Extracellular Polymeric Substances from Shewanella sp. HRCR-1 Biofilms to U(VI) Immobilization,” Environmental Science and Technology, DOI: 10.1021/es200095j.