Müller Hubert, Bosch Julian, Griebler Christian, Damgaard Lars Riis, Nielsen Lars Peter, Lueders Tillmann, Meckenstock Rainer U
Institute of Groundwater Ecology, Helmholtz Zentrum München, Neuherberg, Germany.
Section for Microbiology, Department of Bioscience, Aarhus University, Aarhus C, Denmark.
ISME J. 2016 Aug;10(8):2010-9. doi: 10.1038/ismej.2015.250. Epub 2016 Apr 8.
The biodegradation of organic pollutants in aquifers is often restricted to the fringes of contaminant plumes where steep countergradients of electron donors and acceptors are separated by limited dispersive mixing. However, long-distance electron transfer (LDET) by filamentous 'cable bacteria' has recently been discovered in marine sediments to couple spatially separated redox half reactions over centimeter scales. Here we provide primary evidence that such sulfur-oxidizing cable bacteria can also be found at oxic-anoxic interfaces in aquifer sediments, where they provide a means for the direct recycling of sulfate by electron transfer over 1-2-cm distance. Sediments were taken from a hydrocarbon-contaminated aquifer, amended with iron sulfide and saturated with water, leaving the sediment surface exposed to air. Steep geochemical gradients developed in the upper 3 cm, showing a spatial separation of oxygen and sulfide by 9 mm together with a pH profile characteristic for sulfur oxidation by LDET. Bacterial filaments, which were highly abundant in the suboxic zone, were identified by sequencing of 16S rRNA genes and fluorescence in situ hybridization (FISH) as cable bacteria belonging to the Desulfobulbaceae. The detection of similar Desulfobulbaceae at the oxic-anoxic interface of fresh sediment cores taken at a contaminated aquifer suggests that LDET may indeed be active at the capillary fringe in situ.
含水层中有机污染物的生物降解通常局限于污染物羽流的边缘，在那里电子供体和受体的陡峭反向梯度被有限的扩散混合分隔开来。然而，最近在海洋沉积物中发现了丝状“索状细菌”进行的长距离电子转移（LDET），它能在厘米尺度上耦合空间分离的氧化还原半反应。在此，我们提供了初步证据，表明在含水层沉积物的有氧 - 缺氧界面也能发现这种硫氧化索状细菌，它们通过1 - 2厘米距离的电子转移为硫酸盐的直接循环利用提供了一种方式。沉积物取自受烃污染的含水层，添加硫化铁并用水饱和，使沉积物表面暴露于空气中。在顶部3厘米处形成了陡峭的地球化学梯度，显示出氧气和硫化物在空间上相隔9毫米，同时具有LDET进行硫氧化特征性的pH剖面。通过对16S rRNA基因进行测序和荧光原位杂交（FISH），在缺氧区大量存在的细菌丝被鉴定为属于脱硫弧菌科的索状细菌。在受污染含水层采集的新鲜沉积物岩心的有氧 - 缺氧界面检测到类似的脱硫弧菌科，这表明LDET在原位毛细边缘可能确实活跃。
