Fe(II) is common in anaerobic systems and can be oxidized by bacteria forming a variety of Fe(III) and mixed valent iron oxy-hydroxides, which play a major role in contaminant fate and transport. In addition, adsorption of Fe(II) onto bacterial cell walls may represent the rate-controlling step for biotically induced ferrous oxidation, but there are no studies that quantify either the extent of Fe+2 adsorption onto bacterial cells or the thermodynamic stabilities of the important Fe(II)-bacterial complexes. In this study, we measured Fe(II) adsorption onto two bacterial species: an iron-oxidizing, non-sheath forming Gram-negative bacterial species, Leptothrix cholodnii, and a Gram-positive aerobic soil bacterial species, Bacillus subtilis. The experiments for both species were performed under a nitrogen/hydrogen atmosphere with ionic strength held constant with 0.1 M NaClO4; experiments were conducted as a function of pH over the range of 2 to 11 and biomass concentration and Fe(II) concentration were held at 5 g/L and 10-4.75 M, respectively. Non-adsorbed Fe concentrations were analyzed using ICP-OES. Acidity constants and site concentrations for B. subtilis have been determined previously, but these parameters were determined for L. cholodnii by conducting potentiometric titrations of cell suspensions in 0.1 M NaClO4electrolyte solutions.We observed enhanced removal of Fe(II) under all pH conditions relative to abiotic controls. The adsorption measurements conducted as a function of pH constrain which cell envelope functional groups are involved in Fe(II) binding, and we used the adsorption measurements to determine equilibrium constants for the important adsorption reactions. The thermodynamic parameters determined here not only improve quantitative models of Fe(II) distribution and speciation in geologic systems, but they also can be used to construct quantitative models of Fe(II) bioavailability in bacteria-bearing systems as well, allowing the effects of competing cations and complexing ligands to be accounted for in each model.

Fe(II) adsorption by <i>Bacillus subtilis</i> and <i>Leptothrix cholodnii</i> bacterial cells

246th National Meeting (2013)

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Fe(II) adsorption by Bacillus subtilis and Leptothrix cholodnii bacterial cells