Reduction of Fe(III) colloids by Shewanella putrefaciens: A kinetic model

Abstract

A kinetic model for the microbial reduction of Fe(III) oxyhydroxide colloids in the presence of excess electron donor is presented. The model assumes a two-step mechanism: (1) attachment of Fe(III) colloids to the cell surface and (2) reduction of Fe(III) centers at the surface of attached colloids. The validity of the model is tested using Shewanella putrefaciens and nanohematite as model dissimilatory iron reducing bacteria and Fe(III) colloidal particles, respectively. Attachment of nanohematite to the bacteria is formally described by a Langmuir isotherm. Initial iron reduction rates are shown to correlate linearly with the relative coverage of the cell surface by nanohematite particles, hence supporting a direct electron transfer from membrane-bound reductases to mineral particles attached to the cells. Using internally consistent parameter values for the maximum attachment capacity of Fe(III) colloids to the cells, M max , the attachment constant, K P , and the first-order Fe(III) reduction rate constant, k, the model reproduces the initial reduction rates of a variety of finegrained Fe(III) oxyhydroxides by S. putrefaciens. The model explains the observed dependency of the apparent Fe(III) half-saturation constant, K Ã m , on the solid to cell ratio, and it predicts that initial iron reduction rates exhibit saturation with respect to both the cell density and the abundance of the Fe(III) oxyhydroxide substrate.

Microbiological Controls on Geochemical Kinetics 1: Fundamentals and Case Study on Microbial Fe(III) Oxide Reduction

“…8.15c). Previous work by Caccavo (2000, 2001), as well as a recent study by Bonneville et al (2006), revealed qualitatively similar results for the association of Fe(III) oxides with DIRM cell surfaces, and the relationship between oxide-adhered DIRM cell density and Fe(III) reduction rate. The association of DIRMs with Fe(III) oxides is probably driven by hydrophobic rather than electrostatic forces, since both DIRM cells and Fe(III) oxides bear a net negative charge at pH (Caccavo et al, 1997;Caccavo, 2000, 2001).…”

“…1 in (Caccavo, 1999;Caccavo and Das, 2002). Current evidence suggests that the latter components are required for the irreversible adhesion of Fe(III) oxides to DIRM cells (Caccavo and Das, 2002) that has been observed in several studies (Bonneville et al, 2006;Caccavo, 1999;Caccavo et al, 1996;Glasauer et al, 2001). However, irreversible adhesion is not required for enzymatic reduction to take place (Caccavo et al, 1997;Caccavo and Das, 2002;Grantham et al, 1997), and detachment and transport of DIRM cells clearly takes place in hydrologically open reaction systems Roden et al, 2000).…”

Nanosized Iron Oxide Colloids Strongly Enhance Microbial Iron Reduction

“…It has been shown before that the iron oxide-microorganism contact area has an impact on reduction rates (3). Colloids constantly undergo Brownian movement, probably increasing their potential for capturing electrons from the cell surface by higher numbers of contact events with reactive sites at the microbial cell surface, although there is also a potential for long-term attachment of nanoparticles to iron-reducing cells (3). Another aspect might be that colloidal particles have the potential to fully cover the bacterial cell following a Langmuir isotherm (3), as opposed to bulk ferric iron phases, which probably cannot cover the cell due to a spatial limitation.…”

“…Naturally, well crystalline minerals have lower surface areas, and the effects of surface area and solubility cannot be distinguished sharply. Cell density, initial oxide and substrate concentrations, and ferrous iron adsorbed to the bulk mineral surface were also reported to control microbial reduction rates by exhibiting mutual saturation behavior in Michaelis-Mententype kinetics (3,22,40).…”

Adsorption and surface oxidation of Fe(II) on metal (hydr)oxides

“…Reduced conditions are maintained in water-logged soils and sediments due to back-consumption of oxygen and organic carbon by chemotrophic microorganisms. The rate of Fe(II) production by micro-organisms depends on the surface area of the ferric (hydr)oxide that is in contact with micro-organisms (Bonneville et al, 2006). Under intermediate redox conditions (10 < pe < 0) and neutral pH values, iron can be present as aqueous Fe(II) in combination with Fe(III) (hydr)oxides.…”