392 Fractionation of Cu Isotopes During Adsorption and Metabolic Uptake by Bacteria

Friday, November 6, 2009: 10:20 AM
Charolais (Camino Real Hotel)
Jesica Urbina Navarrete , Department of Environmental Science, University of Texas at El Paso, El Paso, TX
David Borrok , Department of Geological Sciences, University of Texas at El Paso, El Paso, TX
The isotopic composition of transition metals such as Cu can vary substantially in natural waters, soils and rocks. Cu isotopes can be fractionated during various transformations, including adsorption, precipitation and redox reactions. Hence, the Cu isotopic composition (d65Cu) of environmental samples can be used not only to track metal sources, but to identify reaction mechanisms. Reactions involving organic and biological constituents are of particular importance in controlling the availability and transport of Cu. Microorganisms play important roles as natural sinks for metals.
In this investigation, we develop isotopic fractionation factors for Cu-bacteria interactions, including reversible surface adsorption (which may be a proxy for complexation with dissolved organic molecules) and intracellular uptake. Adsorption experiments were conducted with Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria over numerous Cu:bacteria ratios and over the pH range 2.5 to 6. Bacterial growth experiments designed to isolate intracellular Cu from surface adsorption reactions were also conducted. Isotopic results indicate that reversible adsorption with bacterial surfaces result in a separation factor, Δ65Cusolid-solution, of about +0.8‰ for B. subtilis and about +1.3‰ for E. coli, while intracellular incorporation results in a separation factor, Δ65Cusolid-solution, around –1.0‰. These initial isotopic results demonstrate that substantial fractionation of the Cu isotopes occurs both during surface adsorption and intracellular uptake with bacteria, but that the direction of fractionation appears to be opposite for each process. We are currently expanding on these initial isotope measurements and will report our latest results for both adsorption and uptake reactions.