Effect of initial pH value on microbial Fe（III）reduction in alkaline and acidic paddy soils

Chao, 吴超 Wu; Dong, 曲东 Qu; Hao, 刘浩 Liu

doi:10.5846/stxb201210091394

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“…Alkaline soils are widely distributed in China (4.49 million hm 2 ) as well, accounting for 46.8 % of the total terrestrial area of China (IGBP-DIS 1998). The investigation of the mechanism for Fe(III) reduction under alkaline conditions is therefore important., Microbial Fe(III) (oxyhydr)oxide reduction has been observed in some alkaline environments such as soils, sediments, groundwater and lakes (Zavarzina et al 2006;Burke et al 2012;Thorpe et al 2012;Chao et al 2014), but the mechanism has not been clearly identified. Elemental sulfur (S 0 ) was reported to be an electron shuttle to expedite goethite reduction by Shewanella oneidensis MR-1 at pH 9.0 and this S 0 -mediated electron transfer pathway was postulated to be an important mechanism for iron reduction under alkaline conditions with a relatively high S 0 level (Flynn et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Electron shuttle-mediated microbial Fe(III) reduction under alkaline conditions

Wang

Sun

et al. 2017

J Soils Sediments

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Purpose: Extracellular Fe(III) reduction plays an important role in a variety of biogeochemical processes. Several mechanisms for microbial Fe(III) reduction in pH-neutral environments have been proposed, but pathways of microbial Fe(III) reduction within alkaline conditions have not been clearly identified. Alkaline soils are vastly distributed; thus, a better understanding of microbial Fe(III) reduction under alkaline conditions is of significance. The purpose of this study is to explore the dominant mechanism of bacterial iron reduction in alkaline environments. Materials and methods: We used antraquinone-2,6-disulfonate (AQDS) as a representative of quinone moities of humic substances and elemental sulfur and sulfate as sulfur species to investigate the potential role of humic substances and sulfur species in mediating microbial Fe(III) reduction in alkaline environments. We carried out thermodynamic calculations to predict the ability of bacteria to reduce Fe(III) (oxyhydr)oxides under alkaline conditions and the ability of AQDS and sulfur species to serve as electron acceptors for microbial anaerobic respiration in an assumed alkaline soil environments. A series of incubation experiments with two model dissimilatory metal reducing bacteria, Shewanella oneidensis MR-1 and Geobacter sulfurreducens PCA as well as mixed bacteria enriched from a soil were performed to confirm the contribution of AQDS and sulfur species to Fe(III) reduction under alkaline conditions. Results and discussion: Based on thermodynamic calculations, we predicted that, under alkaline conditions, the enzymatic reduction of Fe(III) (oxyhydr)oxides would be thermodynamically feasible but very weak. In our incubation experiments, the reduction of ferrihydrite by anaerobic cultures of Shewanella oneidensis MR-1, Geobacter sulfurreducens PCA or microbes enriched from a soil was significantly increased in the presence of S0 or AQDS. Notably, AQDS contributed more to promoting Fe(III) reduction as a soluble electron shuttle than S0 did under the alkaline conditions probably because of different mechanisms of microbial utilization of AQDS and S0. Conclusions: These results suggest that microbial reduction of Fe(III) (oxyhydr)oxides under alkaline conditions may proceed via a pathway mediated by electron shuttles such as AQDS and S0. Considering the high ability of electron shuttling and vast distribution of humic substances, we suggest that humic substance-mediated Fe(III) reduction may potentially be the dominant mechanism for Fe(III) reduction in alkaline environments

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Section: Introductionmentioning

confidence: 99%