Collaborative Research: Interactions of Heavy Metals With Biofilm-Coated Mineral Surfaces

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Brown/Sporman9905755Microbial biofilms are common coatings on mineral surfaces in many environments and are known to sorb metal ions such as Pb(II). However, little is currently known about the chemical form(s) of these metal ions at a molecular level, their spatial distribution in the biofilm, and the mechanisms by which the biofilm affects metal ion sorption on mineral surfaces. This multidisciplinary project will address these and related issues through laboratory studies of Pb(II) sorption on biofilm-coated surfaces of aluminum and iron (hydr)oxides and quartz as a function of several solution variables. The molecular-scale speciation and spatial distribution of Pb(II) in biofilms grown on these surfaces will be studied using synchrotron-based x-ray and electron microscopy methods. In addition, we will use infrared spectroscopy to study the effects on Pb(II) uptake of the common inorganic ligand PO43- and several organic ligands that are dominant functional groups on bacterial surfaces and biofilm exopolysaccharides. Burkholderia cepacia, an aerobic gram-negative bacterium that readily forms biofilms under nutrient-limited conditions, was chosen for the initial phases of this work. Our choice of system variables will be guided by the results of our ongoing studies of Pb speciation in several Pb-contaminated tailings at Leadville, CO and soils in northern France. The role of extracellular phosphate and of intracellular ortho- and polyphosphate metabolism in the biofilm in producing Pb-phosphates will be explored. Our approach starts with relatively simplified model systems and systematically adds some of the complexities of natural systems. The ultimate goal of this work is to develop a fundamental understanding of some of the factors that control the geochemical cycling (and potential bioavailability) of Pb and other metals in aquatic environments.This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry solicitation NSF 99-9, and is being funded jointly by the Divisions of Chemistry, Earth Sciences, Ocean Sciences, and MPS Office of Multidisciplinary Activities.