The mechanisms of iron isotope fractionation produced during dissimilatory Fe(III) reduction by Shewanella putrefaciens and Geobacter sulfurreducens
The mechanisms of iron isotope fractionation produced during dissimilatory Fe(III) reduction by Shewanella putrefaciens and Geobacter sulfurreducens
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DOI：
10.1111/j.1472-4669.2007.00103.x
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发表时间：
2007-06-01
期刊：
影响因子：
3.7
通讯作者：
Beard, Brian L.
中科院分区：
文献类型：
--
作者：
Crosby, Heidi A.;Roden, Eric E.;Beard, Brian L.
微生物异化铁还原 (DIR) 在厌氧沉积物中广泛存在，是含有活性氧化铁的低氧沉积物中水性 Fe(II) 的主要产生者。先前的研究表明，DIR 产生了一些最大的稳定铁同位素自然分馏，尽管这种同位素分馏的机制尚不清楚。在这里，我们比较了硫还原地杆菌菌株 PCA 和腐败希瓦氏菌菌株 CN32 的相似培养物在赤铁矿和针铁矿还原过程中产生的铁同位素分馏。两种物质都会产生重 Fe 同位素耗尽的水性 Fe(II)，如 Fe-56/Fe-54 比率或 Delta Fe-56 值的减少所表示。 DIR 产生的水性 Fe(II) 的低 Delta Fe-56 值反映了三种 Fe 库存之间的同位素交换：水性 Fe(II) (Fe(II)(aq))、吸附的 Fe(II) (Fe(II)(sorb)) 和氧化铁表面上的反应性 Fe(III) 组分 (Fe(III),ad。Fe(II)(aq) 和 Fe(II)(aq) 之间 Fe-56/Fe-54 比率的分馏Fe(III)(reac) 为 -2.95 ppm，并且在实验时间尺度（280 d）内保持恒定。 Fe(II)(aq) - Fe(III)(reac) 分馏与铁 Fe 底物（赤铁矿或针铁矿）和细菌种类无关，表明 DIR 过程中 Fe(II)(aq) - Fe(III)(reac) 分馏的常见机制。 Fe-56/Fe-54 比率确定 DIR 在室温下与非生物系统中的平衡 Fe(II)(aq) - 三氧化二铁分馏的误差范围内是相同的，这表明细菌在 DIR 过程中产生 Fe 同位素分馏的作用在于催化 Fe(II)(aq) 和 Fe(III)(reac) SO 之间的耦合原子和电子交换，从而发生平衡 Fe 同位素分配。 Fe(II)(aq) 和 Fe(III)(reac) 保持不变，Fe(II)(aq) 的绝对δ值随着 Fe(II)(aq)、Fe(II)(sorb) 和 Fe(III)(reac) 的相对比例而变化，在还原过程中，这些比例的时间变化是赤铁矿或针铁矿特有的，但与细菌种类无关。 Fe(II)(aq) - Fe(II)(sorb) 分馏率为 Fe-56/Fe-54 比例中的 -0.30 ppm，再加上 Fe(II)(sorb) 比例较小，产生了微不足道的 (
Microbial dissimilatory iron reduction (DIR) is widespread in anaerobic sediments and is a key producer of aqueous Fe(II) in suboxic sediments that contain reactive ferric oxides. Previous studies have shown that DIR produces some of the largest natural fractionations of stable Fe isotopes, although the mechanism of this isotopic fractionation is notyetwell understood. Here we compare Fe isotope fractionations produced by similar cultures of Geobacter sulfurreducens strain PCA and Shewanella putrefaciens strain CN32 during reduction of hematite and goethite. Both species produce aqueous Fe(II) that is depleted in the heavy Fe isotopes, as expressed by a clecrease in Fe-56/Fe-54 ratios or delta Fe-56 values. The low delta Fe-56 values for aqueous Fe(II) produced by DIR reflect isotopic exchange among three Fe inventories: aqueous Fe(II) (Fe(II)(aq)), sorbed Fe(II) (Fe(II)(sorb)), and a reactive Fe(III) component on the ferric oxide surface (Fe(Ill),ad. The fractionation in Fe-56/Fe-54 ratios between Fe(II)(aq) and Fe(III)(reac) was -2.95 parts per thousand, and this remained constant over the timescales of the experiments (280 d). The Fe(II)(aq) - Fe(III)(reac) fractionation was independent of the ferric Fe substrate (hematite or goethite) and bacterial species, indicating a common mechanism for Fe isotope fractionation during DIR. Moreover, the Fe(II)(aq) - Fe(III)(reac) fractionation in Fe-56/Fe-54 ratioscluring DIR is identical within error of the equilibrium Fe(II)(aq) - ferric oxide fractionation in abiological systems at room temperatures. This suggests that the role of bacteria in producing Fe isotope fractionations during DIR lies in catalyzing coupled atom and electron exchange between Fe(II)(aq) and Fe(III)(reac) SO that equilibrium Fe isotope partitioning occurs.Although Fe isotope fractionation between Fe(II)(aq) and Fe(III)(reac) remained constant, the absolute delta Fe-56,;alues for Fe(II)(aq) varied as a function of the relative proportions of Fe(II)(aq), Fe(II)(sorb), and Fe(III)(reac), during reduction. The temporal variations in these proportions were unique to hematite or goethite but independent of bacterial species. In the case of hematite reduction, the small measured Fe(II)(aq) - Fe(II)(sorb) fractionation of -0.30 parts per thousand in Fe-56/ Fe-54 ratios, combined with the small proportion of Fe(II)(sorb), produced insignificant (