Reduction of Structural Fe(III) in Smectite by a Pure Culture of Shewanella Putrefaciens Strain MR-1

Abstract

Abstraet--Shewanella putrefaciens is a species of metal-reducing bacteria with a versatile respiratory metabolism. This study reports that S. putrefaciens strain MR-1 rapidly reduces Fe(III) within smectite clay minerals. Up to 15% of the structural Fe within ferruginous smectite (sample SWa-1, Source Clays Repository of the Clay Minerals Society) was reduced by MR-1 in 4 h, and a range of 25% to 41% of structural Fe was reduced after 6 to 12 d during culture. Conditions for which smectite reduction was optimal, that is, pH 5 to 6, at 25 to 37 ~ are consistent with an enzymatic process and not with simple chemical reduction. Smectite reduction required viable cells, and was coupled to energy generation and carbon metabolism for MR-1 cultures with smectite added as the sole electron acceptor. Iron(III) reduction catalyzed by MR-1 was inhibited under aerobic conditions, and under anaerobic conditions it was inhibited by the addition of nitrate as an alternate electron acceptor or by the metabolic inhibitors tetrachlorosalicylanilide (TCS) or quinacrine hydrochloride. Genetic mutants of MR-1 deficient in anaerobic respiration reduced significantly less structural Fe than wild-type cells. In a minimal medium with formate or lactate as the electron donor, more than three times the amount of smectite was reduced over no-carbon controls. These data point to at least one mechanism that may be responsible for the microbial reduction of clay minerals within soils, namely, anaerobic respiration, and indicate that pure cultures of MR-1 provide an effective model system for soil scientists and mineralogists interested in clay reduction. Given the ubiquitous distribution and versatile metabolism of MR-I, these studies may have further implications for bioremediation and water quality in soils and sediments.

Review on iron availability in soil: interaction of Fe minerals, plants, and microbes

“…With respect to the Fe geochemistry in soil, MS s are able to react directly with the surfaces of Fe minerals mobilizing the micronutrient via a complexation process (Kostka et al 1996). The insoluble Fe sources mainly subjected to weathering by MS s are Fe-containing primary silicates and Fe (hydr)oxides (Kraemer 2004).…”

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…Depending on the Si(OH) 4 concentration produced, this can trigger the precipitation of layered silicates such as smectites, glauconite and celadonite as well as silica (Bjorlykke, 2010;Charpentier et al, 2011;Gaudin et al, 2005;Polgári et al, 2013;Pufahl and Hiatt, 2012;Zijlstra, 1995). Similar to HA, the clay mineral formation within the sediment and the use of the redox potential of these authigenic minerals are, at least in part, the result of microbial action (Konhauser and Urrutia, 1999;Kostka et al, 1996).…”

Microbial ecology meets electrochemistry: electricity-driven and driving communities

“…One example of a niche in which nanowires might play a role is that of sediments rich in iron-rich clays. In such clays, substantial reduction of interlayer iron is observed (Kostka et al, 1996(Kostka et al, , 1999. This process could be carried out via electron shuttles, by the use of some iron-binding compounds like siderophores to transport the iron out of the clays, or perhaps by nanowires.…”