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结论
我们检查了 Fe(III) 羟基氧化物表面上次生 Fe 矿物的表面结壳的存在，这可能会限制微生物 Fe (III) 还原的程度。 淡水沉积物的特征是水铁矿占主导地位的表层含有生物茎和鞘。 1 和 2 厘米深度的 16S rRNA 基因分析结果检测到 Fe(II) 氧化细菌 Gallionellaceae。 在 2-4 厘米的沉积物深度处，孔隙水 Fe2+ 浓度显着增加。 在 1、2 和 4 厘米的沉积物深度检测到异化 Fe(III) 还原菌。 根据 EXAFS 结果，建议菱铁矿和针铁矿在 3 cm 以下的深度沉淀。 然而，仅在 3 至 4 cm 深度之间观察到 Fe 矿物组成的变化，并且大部分水铁矿保持在 4 cm 以下的深度。 6 cm 以下深度浓度增加。 孔隙水中生物质的稳定同位素分析表明，7 cm以下深度存在乙酰碎屑生物质，这种生物质的产生通常受到异化Fe(III)还原的抑制。 16S rRNA 基因分析的结果表明，在 10 厘米深度处存在产甲烷古菌 Methanosarcinales。 这些结果表明，在 4 cm 以下深度水铁矿的不完全还原不是由于缺乏有机碳。 TEM 观察表明，茎和鞘表面的 Fe 矿物从 1 cm 深度的水铁矿转变为 3 cm 以下深度的菱铁矿和针铁矿。 此外，通过 CEYEXAFS 分析在 10 厘米深度处定量铁矿物形态表明针铁矿主要存在于颗粒表面。 这些结果不同于大量 EXAFS 分析结果，即水铁矿是主要的铁矿物种类。 根据这些结果，水铁矿表面可能被针铁矿包裹，这可能限制了水铁矿在 4 cm 深度以下的还原程度。
致谢
我们感谢 M. Miyazaki 博士和 K. Yanagawa 博士在构建系统发育树方面提出的善意建议。 本研究由 JSPS 青年科学家研究奖学金资助。 这项工作也得到了 SPring-8 (2012A1589, 2013A1613, 2014A1416) 和 KEK (2013G052, 2013G562) 的支持。
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支持信息
Additional Supporting Information may be found in the online version of this article:
Fig. S1. Representative SEM images of sediment at 1 cm (A), 3 cm (B), 5 cm (C), 7 cm (D), and 9 cm (E).
Fig. S2. The XRD patterns of sediment up to 10 cm depths.
