Nanosized Iron Oxide Colloids Strongly Enhance Microbial Iron Reduction

Abstract

Microbial iron reduction is considered to be a significant subsurface process. The rate-limiting bioavailability of the insoluble iron oxyhydroxides, however, is a topic for debate. Surface area and mineral structure are recognized as crucial parameters for microbial reduction rates of bulk, macroaggregate iron minerals. However, a significant fraction of iron oxide minerals in the subsurface is supposed to be present as nanosized colloids. We therefore studied the role of colloidal iron oxides in microbial iron reduction. In batch growth experiments with Geobacter sulfurreducens, colloids of ferrihydrite (hydrodynamic diameter, 336 nm), hematite (123 nm), goethite (157 nm), and akaganeite (64 nm) were added as electron acceptors. The colloidal iron oxides were reduced up to 2 orders of magnitude more rapidly (up to 1,255 pmol h ؊1 cell ؊1 ) than bulk macroaggregates of the same iron phases (6 to 70 pmol h ؊1 cell ؊1 ). The increased reactivity was not only due to the large surface areas of the colloidal aggregates but also was due to a higher reactivity per unit surface. We hypothesize that this can be attributed to the high bioavailability of the nanosized aggregates and their colloidal suspension. Furthermore, a strong enhancement of reduction rates of bulk ferrihydrite was observed when nanosized ferrihydrite aggregates were added.

Archaea catalyze iron-dependent anaerobic oxidation of methane

“…Ferrihydrite and birnessite were synthesized according to protocols described previously (23,38). Briefly, for ferrihydrite, 21 g of ferric citrate (Sigma) was dissolved in 300 mL MilliQ water by vigorous stirring while being kept at 80°C.…”

“…Using marine samples, Nauhaus et al reported that methane oxidation was not coupled to the reduction of ferrihydrite, iron citrate, humic acids, and anthraquinone-2,6-disulfonate (AQDS) (21), whereas recently Scheller et al showed that marine samples containing ANME-2a, ANME-2c, and other archaea oxidized methane in the presence of chelated iron and could couple methane oxidation activity to AQDS reduction (22). Nevertheless, in nature, metals predominantly occur in particulate forms, which are more difficult to access (15,16,19,23). In short, the microorganisms that can couple the oxidation of methane to the reduction of environmentally relevant species of oxidized metals remain unknown.…”

“…In nature, iron reduction is often limited by the bioavailability of iron oxides, and soluble or complexed Fe 3+ is scarce (19,23). Therefore, we also incubated the enrichment culture with more environmentally relevant forms of oxidized metals: nanoparticulate ferrihydrite (Fe 3+ ) and birnessite (Mn 4+ ).…”

Iron-Reducing Bacteria and Iron Nanostructures

“…Due to their wide occurrence, tendency to nucleate and grow on the surfaces of other phases, important redox capabilities, and relatively high reactivity iron nanostructures have important roles in biogeochemical processes [23]. On the other hand iron nanostructures have gained wide applications in various sciences and particularly in biomedical sciences.…”

Synthesis, Characterization, and Magnetic Studies ofα-Fe2O3Arora1, Sharma2, Kumari3 et al. 2014Journal of Nanotechnology15090View full textAdd to dashboardCite

“…Nanosized iron oxide has applications in waste water treatment and as sensors. Role of nanosized colloidal iron oxides in microbial iron reduction has been studied [20]. Implications of heat treatment on the 2 Journal of Nanotechnology properties of a magnetic iron oxide-titanium dioxide photocatalyst have been studied [21].…”