title: Biological redox cycling of iron in nontronite and its potential application in nitrate removal.
abstract: Biological redox cycling of structural Fe in phyllosilicates is an important but poorly understood process. The objective of this research was to study microbially mediated redox cycles of Fe in nontronite (NAu-2). During the reduction phase, structural Fe(III) in NAu-2 served as electron acceptor, lactate as electron donor, AQDS as electron shuttle, and dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens CN32 as mediator in bicarbonate- and PIPES-buffered media. During the oxidation phase, biogenic Fe(II) served as electron donor and nitrate as electron acceptor. Nitrate-dependent Fe(II)-oxidizing bacterium Pseudogulbenkiania sp. strain 2002 was added as mediator in the same media. For all three cycles, structural Fe in NAu-2 was able to reversibly undergo three redox cycles without significant dissolution. Fe(II) in bioreduced samples occurred in two distinct environments, at edges and in the interior of the NAu-2 structure. Nitrate reduction to nitrogen gas was coupled with oxidation of edge-Fe(II) and part of interior-Fe(II) under both buffer conditions, and its extent and rate did not change with Fe redox cycles. These results suggest that biological redox cycling of structural Fe in phyllosilicates is a reversible process and has important implications for biogeochemical cycles of carbon, nitrogen, and other nutrients in natural environments.
authors: Linduo
authors: L
authors: Zhao
authors: §Geomicrobiology Laboratory, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China.
authors: Hailiang
authors: H
authors: Dong
authors: ⊥Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
authors: Ravi K
authors: RK
authors: Kukkadapu
authors: §Geomicrobiology Laboratory, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China.
authors: Qiang
authors: Q
authors: Zeng
authors: Richard E
authors: RE
authors: Edelmann
authors: ¶Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors: Martin
authors: M
authors: Pentrák
authors: ∥Department of Earth and Environmental Sciences, Wright State University, Dayton, Ohio 45435, United States.
authors: Abinash
authors: A
authors: Agrawal
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D009346:Neisseriaceae / Q000378:metabolism; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D020614:Shewanella putrefaciens / Q000378:metabolism*
chemical_list: D005290:Ferric Compounds; D009566:Nitrates; D007501:Iron