Oberding Lisa K, Gieg Lisa M
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
Appl Environ Microbiol. 2017 Dec 15;84(1). doi: 10.1128/AEM.01773-17. Print 2018 Jan 1.
Paraffinic -alkanes (>C) that are solid at ambient temperature comprise a large fraction of many crude oils. The comparatively low water solubility and reactivity of these long-chain alkanes can lead to their persistence in the environment following fuel spills and pose serious problems for crude oil recovery operations by clogging oil production wells. However, the degradation of waxy paraffins under the anoxic conditions characterizing contaminated groundwater environments and deep subsurface energy reservoirs is poorly understood. Here, we assessed the ability of a methanogenic culture enriched from freshwater fuel-contaminated aquifer sediments to biodegrade the model paraffin -octacosane (CH). Compared with that in controls, the consumption of -octacosane was coupled to methane production, demonstrating its biodegradation under these conditions. was postulated to be an important CH degrader in the culture on the basis of its high relative abundance as determined by 16S rRNA gene sequencing. An identified gene (known to encode the α subunit of alkylsuccinate synthase) aligned most closely with those from other organisms. Quantitative PCR (qPCR) and reverse transcription qPCR assays for demonstrated significant increases in the abundance and expression of this gene in CH-degrading cultures compared with that in controls, suggesting -octacosane activation by fumarate addition. A metabolite analysis revealed the presence of several long-chain α,ω-dicarboxylic acids only in the CH-degrading cultures, a novel observation providing clues as to how methanogenic consortia access waxy hydrocarbons. The results of this study broaden our understanding of how waxy paraffins can be biodegraded in anoxic environments with an application toward bioremediation and improved oil recovery. Understanding the methanogenic biodegradation of different classes of hydrocarbons has important applications for effective fuel-contaminated site remediation and for improved recovery from oil reservoirs. Previous studies have clearly demonstrated that short-chain alkanes (<C) can be biodegraded anaerobically, but less is understood regarding the biodegradation of longer chain waxy alkanes (>C) that comprise many fuel mixtures. Using an enrichment culture derived from a freshwater fuel-contaminated site, we demonstrate that the model waxy alkane -octacosane can be biodegraded under methanogenic conditions by a presumed phylotype. Compared with that of controls, we show an increased abundance and expression of the gene, which is known to be important for anaerobic -alkane metabolism. Metabolite analyses revealed the presence of a range of α,ω-dicarboxylic acids found only in -octacosane-degrading cultures, a novel finding that lends insight as to how anaerobic communities may access waxes as growth substrates in anoxic environments.
在环境温度下呈固态的链烷烃（>C）在许多原油中占很大比例。这些长链烷烃相对较低的水溶性和反应活性，可能导致其在燃油泄漏后在环境中持续存在，并通过堵塞油井给原油开采作业带来严重问题。然而，在受污染的地下水环境和深部地下能源储层的缺氧条件下，蜡质链烷烃的降解情况却鲜为人知。在此，我们评估了从受淡水燃料污染的含水层沉积物中富集的产甲烷培养物对模型链烷烃——二十八烷（CH）的生物降解能力。与对照组相比，二十八烷的消耗与甲烷产生相关联，表明其在这些条件下可被生物降解。基于16S rRNA基因测序确定的高相对丰度，被推测为培养物中一种重要的CH降解菌。一个已鉴定的基因（已知编码烷基琥珀酸合酶的α亚基）与其他生物的该基因序列最为相似。对该基因进行的定量PCR（qPCR）和逆转录qPCR分析表明，与对照组相比，在降解CH的培养物中该基因的丰度和表达显著增加，这表明通过添加富马酸激活了二十八烷。代谢物分析显示，仅在降解CH的培养物中存在几种长链α,ω-二羧酸，这一新颖的发现为产甲烷菌群如何利用蜡质碳氢化合物提供了线索。本研究结果拓宽了我们对蜡质链烷烃在缺氧环境中如何被生物降解的理解，这对于生物修复和提高石油采收率具有重要意义。了解不同类别的碳氢化合物的产甲烷生物降解对于有效修复受燃料污染的场地以及提高油藏采收率具有重要应用价值。先前的研究已清楚表明，短链烷烃（<C）可被厌氧生物降解，但对于构成许多燃料混合物的较长链蜡质烷烃（>C）的生物降解了解较少。利用从受淡水燃料污染场地获得的富集培养物，我们证明模型蜡质烷烃——二十八烷在产甲烷条件下可被一种推测的系统发育型生物降解。与对照组相比，我们发现已知对厌氧链烷代谢很重要的基因的丰度和表达有所增加。代谢物分析显示，仅在降解二十八烷的培养物中存在一系列α,ω-二羧酸，这一新颖的发现有助于深入了解厌氧群落如何在缺氧环境中利用蜡作为生长底物。
