Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University, Columbus, OH, 43210, USA.
Department of Civil and Environmental Engineering, Duke University, Durham, NC, 27708, USA.
ISME J. 2019 Nov;13(11):2690-2700. doi: 10.1038/s41396-019-0466-0. Epub 2019 Jun 26.
In the last decade, extensive application of hydraulic fracturing technologies to unconventional low-permeability hydrocarbon-rich formations has significantly increased natural-gas production in the United States and abroad. The injection of surface-sourced fluids to generate fractures in the deep subsurface introduces microbial cells and substrates to low-permeability rock. A subset of injected organic additives has been investigated for their ability to support biological growth in shale microbial community members; however, to date, little is known on how complex xenobiotic organic compounds undergo biotransformations in this deep rock ecosystem. Here, high-resolution chemical, metagenomic, and proteomic analyses reveal that widely-used surfactants are degraded by the shale-associated taxa Halanaerobium, both in situ and under laboratory conditions. These halotolerant bacteria exhibit surfactant substrate specificities, preferring polymeric propoxylated glycols (PPGs) and longer alkyl polyethoxylates (AEOs) over polyethylene glycols (PEGs) and shorter AEOs. Enzymatic transformation occurs through repeated terminal-end polyglycol chain shortening during co-metabolic growth through the methylglyoxal bypass. This work provides the first evidence that shale microorganisms can transform xenobiotic surfactants in fracture fluid formulations, potentially affecting the efficiency of hydrocarbon recovery, and demonstrating an important association between injected substrates and microbial growth in an engineered subsurface ecosystem.
在过去的十年中，水力压裂技术在非常规低渗透富烃地层中的广泛应用极大地增加了美国和国外的天然气产量。为了在深部地下产生裂缝，将地表来源的流体注入到低渗透性岩石中，引入了微生物细胞和基质。已经研究了一部分注入的有机添加剂，以研究它们在页岩微生物群落成员中支持生物生长的能力；然而，迄今为止，对于复杂的外来有机化合物在这种深部岩石生态系统中如何进行生物转化，人们知之甚少。在这里，高分辨率的化学、宏基因组和蛋白质组学分析表明，广泛使用的表面活性剂在原位和实验室条件下都被与页岩相关的 Halanaerobium 属细菌降解。这些耐盐细菌表现出表面活性剂底物特异性，优先选择聚合的丙氧基化二醇（PPG）和长链的聚氧乙烯烷基醚（AEO），而不是聚乙二醇（PEG）和短链的 AEO。在共代谢生长过程中，通过甲基乙二醛旁路进行反复的末端聚乙二醇链缩短，从而发生酶促转化。这项工作首次证明了页岩微生物可以转化压裂液配方中的外来表面活性剂，这可能会影响烃类回收的效率，并展示了注入的基质与工程地下生态系统中微生物生长之间的重要关联。
