The reduction of the soluble uranyl ion (U(VI)) by metal-reducing bacteria to the uranous ion (U(IV)), which readily precipitates as sparingly soluble U(IV) solid phases, may represent an efficient in situ bioremediation strategy, as metal-reducing bacteria are often found associated with uranium-contaminated subsurfaces. The biogeochemical cycling of uranium is tightly coupled to that of iron due, in part, to the overlapping potentials of the U(VI)/U(IV) and Fe(III)/Fe(II) redox couples. Indeed, pure cultures of metal-reducing bacteria are able to simultaneously reduce iron oxides and U(VI), though decreased rates of uranium reduction in the presence of different forms of iron oxides suggest that iron oxides may divert the flux of electrons from U(VI) to Fe(III). In this study, the geochemical controls on the competitive inhibition of dissimilatory U(VI) reduction by ferrihydrite were investigated with pure cultures of <i>Shewanella putrefaciens</i>. Results reveal that the thermodynamic favorability of ferrihydrite as a terminal electron acceptor is the primary control of the inhibition of dissimilatory U(VI) reduction. However, secondary mineralization of ferrihydrite into more crystalline phases plays an important role in determining the extent of this inhibition. In turn, dissimilatory U(VI) reduction favors the secondary mineralization of ferrihydrite to less reactive solid-phase iron products, highlighting the complex interplay between the biogeochemical cycles of uranium and iron. A biogeochemical kinetic model developed to reproduce the competition between these two respiratory processes demonstrates that the effect of secondary mineralization processes on U(VI) bioreduction should be included into reactive transport models.

Role of secondary mineralization in the competitive inhibition of microbial uranium reduction by iron oxides

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.