Effects of Phosphate on Secondary Mineral Formation During the Bioreduction of Akaganeite (.β-FeOOH): Green Rust Versus Framboidal Magnetite

Abstract

The activity of microorganisms is a key component of the biogeochemical cycle of Fe in natural systems, where green rusts are often observed as products of microbially driven redox processes. To better define the factors that control green rust formation during microbial Fe(III) reduction, we examined the effects of the presence of an electron shuttle [9,10-anthraquinone-2,6-disulfonate (AQDS)] and phosphate on akaganeite ( -FeOOH) bioreduction by the iron(III)-reducing bacterium (IRB) Shewanella putrefaciens CN32. Framboidal magnetite was the principal secondary mineral formed during akaganeite bioreduction in the absence of phosphate; this is the first time framboidal magnetite has been reported as a product of microbial Fe(III) oxide reduction. Framboidal magnetite was less crystalline when formed in the presence of AQDS than without AQDS and over time was further reduced to chukanovite. Carbonate green rust was the primary secondary mineral observed from akaganeite bioreduction in the presence of phosphate, with and without AQDS; however, siderite was also observed in the presence of AQDS. This first report of green rust as a product of akaganeite bioreduction expands the range of Fe(III) oxides that can be transformed to green rust by IRB, suggesting that the reduction of Fe(III) oxides such as ferrihydrite, lepidocrocite, and akaganeite by IRB is a key process leading to the formation of green rusts in aquatic and terrestrial environments.to their ability to reduce a range of pollutants, including chlorinated solvents, nitroaromatics, azo dyes, toxic metals, metallolids, and radionuclides [18][19][20][21][22][23][24][25][26][27][28][29]. B e n t h a m S c i e n c e P u b l i s h e r s F o r P e r s o n a l U s e O n l y N o t F o r D i s t r i b u t i o n

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

“…using akaganeite (ß-FeOOH) or Zn-substituted akaganeite (ß-ZnxFe1-xOOH) during glucose fermentation [47]. In another study, framboidal magnetite is formed as a major product in the presence of an electron shuttle [9,10-anthraquinone-2,6-disulfonate (AQDS)] via akaganeite (β-FeOOH) bioreduction by the iron(III)-reducing bacterium (IRB) S. putrefaciens CN32 [48]. Microbial synthesis has been tested for preparing magnetically recoverable noble metal NP catalysts.…”

“…This process is reversible in co-cultures by the anaerobic Fe(III)-reducing bacterium Geobacter sulfurreducens [105]. The activity of microorganisms is a key component of the biogeochemical cycle of iron in natural systems, where MNPs and green rusts are often observed as products of microbially driven redox processes [48]. Transport of naturally occurring MNPs has been rarely studied.…”

Green Rust: The Simple Organizing &lsquo;Seed&rsquo; of All Life?&nbsp;&nbsp;<strong> </strong>

“…[185] Such metastability may have been strongly supported by orthophosphate (HPO4 2-) which, having a larger ionic diameter of 0.48 nm, tends to be adsorbed on the margins of green rust, and inhibits its oxidation. [170] As we have noted, Gustaf Arrhenius extolled the likely prebiotic virtues of the double layer hydroxides, saying "surface-active DLH minerals expand freely to accommodate molecular complexes of any size. These structures, thus, also serve as compartmental systems with flexible membranes and what may be called primitive cellular metabolic function.…”

“…That the ionic diameter of the phosphate ion at 0.48 nm so exceeds those of the interlayer galleries at ~0.3 nm, causes it to block the GR margins and inhibit its oxidation. [170] However, it has been demonstrated that orthophosphate (Pi) can intercalate into hydrotalcite where it enforces a height of 0.37 nm. [170.171] We speculate that protons ramming from the acidulous ocean would drive a portion of this phosphate into the hydrous interlayers of the green rust DLH.…”

Frankenstein or a Submarine Alkaline Vent: Who is Responsible for Abiogenesis?

“…The same system on the early Earth when the ocean was carbonic would have imposed a disequilibrium of four or more pH units across barriers of green rust and subsidiary iron sulfide, as well as fully biological redox gradients of usable strength and biological orientation (e.g., as H 2 , HCOO − , and CH 4 inside and NO 3 − outside) (Figure and 2) Green rust is dosed with Ni and Co, intercalated with [MoS 4 ] 2− and often coated with phosphate . These functional elements are also found in proteins, as co‐factors, and are responsible for much of the bioenergetic transformations of extant biology, including electron bifurcation …”