Uranium Biominerals Precipitated by an Environmental Isolate of <i>Serratia</i> under Anaerobic Conditions

<div><p>Stimulating the microbially-mediated precipitation of uranium biominerals may be used to treat groundwater contamination at nuclear sites. The majority of studies to date have focussed on the reductive precipitation of uranium as U(IV) by U(VI)- and Fe(III)-reducing bacteria such as <i>Geobacter</i> and <i>Shewanella</i> species, although other mechanisms of uranium removal from solution can occur, including the precipitation of uranyl phosphates via bacterial phosphatase activity. Here we present the results of uranium biomineralisation experiments using an isolate of <i>Serratia</i> obtained from a sediment sample representative of the Sellafield nuclear site, UK. When supplied with glycerol phosphate, this <i>Serratia</i> strain was able to precipitate 1 mM of soluble U(VI) as uranyl phosphate minerals from the autunite group, under anaerobic and fermentative conditions. Under phosphate-limited anaerobic conditions and with glycerol as the electron donor, non-growing <i>Serratia</i> cells could precipitate 0.5 mM of uranium supplied as soluble U(VI), via reduction to nano-crystalline U(IV) uraninite. Some evidence for the reduction of solid phase uranyl(VI) phosphate was also observed. This study highlights the potential for <i>Serratia</i> and related species to play a role in the bioremediation of uranium contamination, via a range of different metabolic pathways, dependent on culturing or <i>in situ</i> conditions.</p>