Langley S, Igric P, Takahashi Y, Sakai Y, Fortin D, Hannington M D, Schwarz-Schampera U
Department of Earth Sciences, 140 Louis Pasteur, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
Geobiology. 2009 Jan;7(1):35-49. doi: 10.1111/j.1472-4669.2008.00180.x.
Sediment samples were obtained from areas of diffuse hydrothermal venting along the seabed in the Tonga sector of the Tonga-Kermadec Arc, southwest Pacific Ocean. Sediments from Volcano 1 and Volcano 19 were analyzed by X-ray diffraction (XRD) and found to be composed primarily of the iron oxyhydroxide mineral, two-line ferrihydrite. XRD also suggested the possible presence of minor amounts of more ordered iron (hydr)oxides (including six-line ferrihydrite, goethite/lepidocrocite and magnetite) in the biogenic iron oxides (BIOS) from Volcano 1; however, Mössbauer spectroscopy failed to detect any mineral phases more crystalline than two-line ferrihydrite. The minerals were precipitated on the surfaces of abundant filamentous microbial structures. Morphologically, some of these structures were similar in appearance to the known iron-oxidizing genus Mariprofundus spp., suggesting that the sediments are composed of biogenic iron oxides. At Volcano 19, an areally extensive, active vent field, the microbial cells appeared to be responsible for the formation of cohesive chimney-like structures of iron oxyhydroxide, 2-3 m in height, whereas at Volcano 1, an older vent field, no chimney-like structures were apparent. Iron reduction of the sediment material (i.e. BIOS) by Shewanella putrefaciens CN32 was measured, in vitro, as the ratio of [total Fe(II)]:[total Fe]. From this parameter, reduction rates were calculated for Volcano 1 BIOS (0.0521 day(-1)), Volcano 19 BIOS (0.0473 day(-1)), and hydrous ferric oxide, a synthetic two-line ferrihydrite (0.0224 day(-1)). Sediments from both BIOS sites were more easily reduced than synthetic ferrihydrite, which suggests that the decrease in effective surface area of the minerals within the sediments (due to the presence of the organic component) does not inhibit subsequent microbial reduction. These results indicate that natural, marine BIOS are easily reduced in the presence of dissimilatory iron-reducing bacteria, and that the use of common synthetic iron minerals to model their reduction may lead to a significant underestimation of their biological reactivity.
沉积物样本取自西南太平洋汤加-克马德克海沟汤加海域沿海底的弥漫性热液喷口区域。对1号火山和19号火山的沉积物进行了X射线衍射（XRD）分析，发现其主要由羟基氧化铁矿物——二线水铁矿组成。XRD还表明，1号火山的生物源氧化铁（BIOS）中可能存在少量更有序的铁（氢）氧化物（包括六线水铁矿、针铁矿/纤铁矿和磁铁矿）；然而，穆斯堡尔光谱未能检测到比二线水铁矿结晶度更高的任何矿物相。这些矿物沉淀在大量丝状微生物结构的表面。从形态上看，其中一些结构在外观上与已知的铁氧化菌属Mariprofundus spp.相似，这表明沉积物由生物源氧化铁组成。在19号火山，有一个面积广阔、活跃的喷口区，微生物细胞似乎是形成了高2 - 3米的粘性氢氧化铁烟囱状结构的原因；而在较老的1号火山喷口区，没有明显的烟囱状结构。在体外测量了腐败希瓦氏菌CN32对沉积物物质（即BIOS）的铁还原作用，以[总Fe(II)]:[总Fe]的比例表示。根据该参数，计算出1号火山BIOS的还原速率为0.0521天⁻¹，19号火山BIOS的还原速率为0.0473天⁻¹，以及合成的二线水铁矿——水合氧化铁的还原速率为0.0224天⁻¹。两个BIOS站点的沉积物都比合成水铁矿更容易被还原，这表明沉积物中矿物有效表面积的减小（由于有机成分的存在）不会抑制随后的微生物还原。这些结果表明，在异化铁还原细菌存在的情况下，天然海洋BIOS很容易被还原，并且使用常见的合成铁矿物来模拟其还原可能会导致对其生物反应性的显著低估。
