Methanogens and Their Syntrophic Partners Dominate Zones of Enhanced Magnetic Susceptibility at a Petroleum Contaminated Site
Methanogens and Their Syntrophic Partners Dominate Zones of Enhanced Magnetic Susceptibility at a Petroleum Contaminated Site
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DOI：
10.3389/feart.2021.598172
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发表时间：
2021-03-15
影响因子：
2.9
通讯作者：
Rossbach, Silvia
中科院分区：
文献类型：
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作者：
Beaver, Carol L.;Atekwana, Estella A.;Rossbach, Silvia
地球物理调查记录增强磁化率（MS）内的地下水位波动区在碳氢化合物污染的网站表明，MS可以作为一个代理调查微生物介导的铁还原过程中固有的生物修复。在这里，我们调查了微生物群落组成超过5年的时间在碳氢化合物污染的网站，表现出短暂升高MS响应。我们的目标是确定在MS升高的区域中的关键微生物种群。我们从美国明尼苏达州贝米吉附近的石油污染场地取回沉积物岩心，并对这些岩心进行MS测量。我们还通过高通量16 S rRNA基因扩增子测序从沿着完整核心长度收集的样品中表征了微生物群落组成。我们的空间和时间分析表明，微生物群落组成在整个调查期间基本稳定。此外，我们观察到明显的垂直氧化还原分带从上包气带延伸到饱和带。这些明显的氧化还原分带与主要的微生物代谢过程相伴随：（1）包气带上部以好氧微生物为主;（2）包气带下部以甲烷氧化菌、铁还原菌和铁氧化菌为主;（3）涂抹带以铁还原菌为主;（4）游离产物带以互养菌和产甲烷菌为主。虽然常见的概念是，高MS值是由高磁铁矿浓度，可以通过铁还原菌的活动生物形成，在这里，我们表明，最高的磁化率测量在自由相石油区，其中产甲烷的社区是占主导地位的。这一领域的研究可能有助于新兴的知识，甲烷菌可以切换其代谢从产甲烷铁还原与相关的磁铁矿沉淀在碳氢化合物污染的沉积物。因此，地球物理方法，如MS可能有助于确定区域的铁循环/还原产甲烷菌正在发生。
Geophysical investigations documenting enhanced magnetic susceptibility (MS) within the water table fluctuation zone at hydrocarbon contaminated sites suggest that MS can be used as a proxy for investigating microbial mediated iron reduction during intrinsic bioremediation. Here, we investigated the microbial community composition over a 5-year period at a hydrocarbon-contaminated site that exhibited transient elevated MS responses. Our objective was to determine the key microbial populations in zones of elevated MS. We retrieved sediment cores from the petroleum-contaminated site near Bemidji, MN, United States, and performed MS measurements on these cores. We also characterized the microbial community composition by high-throughput 16S rRNA gene amplicon sequencing from samples collected along the complete core length. Our spatial and temporal analysis revealed that the microbial community composition was generally stable throughout the period of investigation. In addition, we observed distinct vertical redox zonations extending from the upper vadose zone into the saturated zone. These distinct redox zonations were concomitant with the dominant microbial metabolic processes as follows: (1) the upper vadose zone was dominated by aerobic microbial populations; (2) the lower vadose zone was dominated by methanotrophic populations, iron reducers and iron oxidizers; (3) the smear zone was dominated by iron reducers; and (4) the free product zone was dominated by syntrophic and methanogenic populations. Although the common notion is that high MS values are caused by high magnetite concentrations that can be biotically formed through the activities of iron-reducing bacteria, here we show that the highest magnetic susceptibilities were measured in the free-phase petroleum zone, where a methanogenic community was predominant. This field study may contribute to the emerging knowledge that methanogens can switch their metabolism from methanogenesis to iron reduction with associated magnetite precipitation in hydrocarbon contaminated sediments. Thus, geophysical methods such as MS may help to identify zones where iron cycling/reduction by methanogens is occurring.