Smectite Reduction by Shewanella Species as Facilitated by Cystine and Cysteine

Deng Liu, Hailiang Dong, Linduo Zhao, Hongmei Wang

Research output: Contribution to journalArticle

Abstract

Exogenous electron transfer mediators employed by Fe(III)-reducing bacteria are believed to govern the kinetics and equilibrium of bioreduction of Fe(III) in solid phase. In contrast to a large number of studies on humic substances and analog anthraquinone-2,6-disulfonate (AQDS), our knowledge of other potential electron shuttles involved in Fe(III) reduction is limited. The purpose of the present study was to understand the role of cystine and cysteine in reduction of iron-rich smectite (nontronite, NAu-2) by Shewanella species. A series of abiotic and biotic experiments were conducted in nongrowth media (bicarbonate buffered, pH = 7.0). Fe(II) and cysteine concentrations were monitored over the course of the bioreduction experiments with wet chemistry, and the unreduced and reduced nontronites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that all Shewanella species tested here were capable of reducing cystine to cysteine. Either cystine or cysteine amendments significantly stimulated the Fe(III) bioreduction rate and extent. The initial reduction rate was linearly correlated with cystine or cysteine concentration. The reduction extent (18.7-22.3%) calculated from bioreactor with cystine or cysteine was slightly lower than those with AQDS (26.3%). Mineralogical analysis demonstrated that cystine or cysteine facilitated the reaction of smectite to illite as a result of Fe(III) bioreduction. Thus, we concluded that, in our experiments, cystine and cysteine functioned as electron carrier in the smectite reduction systems, and were favorable factors influencing smectite illitization.

Original languageEnglish (US)
Pages (from-to)53-63
Number of pages11
JournalGeomicrobiology Journal
Volume31
Issue number1
DOIs
StatePublished - Jan 1 2014
Externally publishedYes

Keywords

  • electron shuttle
  • microbial iron reduction
  • nontronite
  • smectite illitization

ASJC Scopus subject areas

  • Microbiology
  • Environmental Chemistry
  • Environmental Science(all)
  • Earth and Planetary Sciences (miscellaneous)

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