Microbial effects in promoting the smectite to illite reaction: Role of organic matter intercalated in the interlayer

Abstract

Cysteine and toluene as model organic molecules were intercalated into Fe-rich smectite (nontronite, NAu-2). The illitization of these intercalated smectites as induced by microbial reduction of structural Fe 3+ was investigated. Iron-reducing bacterium Shewanella putrefaciens CN32 was incubated with lactate as the sole electron donor and structural Fe 3+ in cysteine-and toluene-intercalated NAu-2 (referred to as cysteine-NAu-2 and toluene-NAu-2 hereafter) as the sole electron acceptor. Anthraquinone-2, 6-disulfonate (AQDS) was used as an electron shuttle in bicarbonate buffer. The extent of Fe 3+ reduction in cysteine-NAu-2 and toluene-NAu-2 was 15.7 and 5.4%, respectively, compared to 20.5% in NAu-2 without organic matter intercalation. In the bioreduced NAu-2, X-ray diffraction, and scanning and transmission electron microscopy did not detect any discrete illite, although illite/ smectite mixed layer or high charge smectite phases were observed. In bioreduced cysteine-NAu-2, discrete illite and siderite formed. In contrast, bioreduction of toluene-NAu-2 did not result in any mineralogical changes. The contrasting bioreduction results between cysteine-and toluene-intercalated nontronite may be ascribed to the nature of organic matter-bacteria interactions. Whereas cysteine is an essential amino acid for bacteria and can also serve as an electron shuttle, thus enhancing the extent of Fe 3+ bioreduction and illitization, toluene is toxic and inhibits Fe 3+ -reducing activity. This study, therefore, highlights the signifi cant role of organic matter in promoting the smectite to illite reaction under conditions typical of natural environments (i.e., non-growth condition for bacteria).

Low-temperature feldspar and illite formation through bioreduction of Fe(III)-bearing smectite by an alkaliphilic bacterium

“…Nevertheless, the ultimate reduction extent (26.2%) was similar to that achieved by S. putrefaciens CN32 (Jaisi et al, 2005;Zhang et al, 2007a). Incomplete reduction of structural Fe(III) in various clay minerals has been observed for other types of bacteria (Kostka et al, 1996;Dong et al, 2009;Ribeiro et al, 2009;Bishop et al, 2011;Liu et al, 2011Liu et al, , 2012Liu et al, , 2014Dong, 2012).…”

“…This S-I reaction was interpreted to occur as a result of microbial reduction of structurally-coordinated Fe(III) in smectite by DIRB, reductive dissolution of smectite, and subsequent formation of illite (Kim et al, 2004). A growing body of work has subsequently suggested that a wide variety of DIRB (e.g., Shewanella strains: Zhang et al, 2007a;Gaines et al, 2009;Jaisi et al, 2011;Koo et al, 2014;Liu et al, 2014;Thermoanaerobacter ethanolicus: Zhang et al, 2006, 2007bThermus scotoductus: Jaisi et al, 2011) and sulfate-reducing bacteria (SRB) (Liu et al, 2012) catalyze illite formation via a similar mechanism. In addition to illite, some other secondary minerals have also been observed as a result of bioreduction of iron-bearing smectite, such as amorphous silica globules (Dong et al, 2003;O'Reilly et al, 2005;Zhang et al, 2007b;Liu et al, 2011Liu et al, , 2014, high charge smectite with increased Al/Si ratios (O'Reilly et al, 2005;Zhang et al, 2007a;Liu et al, 2011), and other various byproducts (e.g., vivianite, siderite, calcite, and iron sulfide particle), depending on medium and buffer type (Li et al, 2004;Dong et al, 2009;Jaisi et al, 2011).…”

The role of Fe(III) bioreduction by methanogens in the preservation of organic matter in smectite

“…Previous research has shown that the type of organic matter may determine the degree of mineralogical changes (Zhang et al, 2007a). When the intercalated organic matter was an essential nutrient for microbes (such as amino acid), its presence would be attractive to microbes and could result in a higher extent of bioreduction to promote mineralogical change.…”

“…Chemically, hydrazine and dithionite are common reductants for Fe(III) (Rozenson and Heller-Kallai, 1976;Stucki et al, 1984;Lee et al, 2006). Biologically, since the isolation of dissimilatory Fe(III) reducing bacteria (DIRB) in 1980s (Lovley and Philips, 1988;Myers and Nealson, 1988), numerous studies have demonstrated that a variety of anaerobic microorganisms are capable of iron reduction in iron-bearing clay minerals, including typical DIRB (Kostka et al, 1996;Lovley et al, 1998;Dong et al, 2003;Zhang et al, 2007a), sulfate-reducing bacteria (Li et al, 2004;Liu et al, 2012), and even methanogens (Liu et al, 2011a;Zhang et al, 2012). The reduction of structural iron in clay minerals can result in important changes in the physical and chemical properties of these minerals, such as layer charge, degree of swelling, and surface area (Stucki, 2011).…”

Microbial reduction of iron(III)-rich nontronite and uranium(VI)

“…Scanning electron microscopy (SEM) samples were prepared in an anoxic glovebox following a previously published procedure (Zhang et al, 2007a). Briefly, cellmineral suspensions were fixed in anoxic 2.5% glutaraldehyde, placed on a glass cover slip, and mineral particles were allowed to settle onto the cover slip for 15 min.…”