Collaborative Research: Investigating the Lost City as an ultramafic urban center of the subseafloor, fueled by energy and carbon from the mantle

绝大多数深海海底沉积物都生活在微生物群落中，这些微生物群落在极端的能量限制下生存，明显的生成时间从几个世纪到几千年。热液系统与这些能源匮乏的环境形成了鲜明的对比，可能代表着海洋次表层重要的、高活动的人口中心。当来自地幔的岩石被抬升并暴露在水中时，所产生的反应导致含有高浓度氢的酸性流体。在某些情况下，在没有生物的情况下，也可以形成甲烷等有机小分子。这些化合物可以为海底微生物群落提供能量，鉴于地幔岩石无处不在，这种反应可能会为活跃的地下生物圈的相当大一部分提供燃料。目前的项目将使用远程操作工具来描述这类系统的一个标志性例子--失落的城市热液领域中的微生物群落。《失落之城》中的幽灵尖顶非常上镜，曾出现在专业纪录片中。探险期间收集的高清水下视频片段将为为期8周的数字媒体教育培训项目提供原材料，培训对象为幼儿园到12年级的高中生和本科生。由此产生的短纪录片将在YouTube和犹他州教育网上发布。地幔岩石构成了海底的很大一部分，其中的微生物群落可能是地球深处和表面生物圈之间碳和能量交换的重要媒介。当构造抬升和暴露在水中时，这些物质的蛇纹岩作用以氢、甲烷和热的形式释放势能，这些产物的进一步反应可以支持有机小分子的非生物合成。然而，最近的研究强调了在这些系统中发现的能够在高pH(9-11)和高温下生存的嗜碱微生物的缺乏。几乎完全缺乏二氧化碳(CO2)是对增长的第二个限制，可能也是更重要的限制。为了更好地了解蛇纹岩地下的范围，该项目将解决这个问题：是什么限制了蛇纹岩地下的生物活动？具体地说，拟议的工作将检验假设：(1)微生物多样性跨越比目前公认的更广泛的温度-pH条件范围，(2)二氧化碳的稀缺是蛇纹岩作用驱动的生态系统的一个关键生物学限制，可以通过一个或几个基础物种的代谢活动来克服。这些假设将在对失落的城市热液领域的20天(现场10天)探险期间得到验证，重点是流体作为地下生物圈的窗口。采样方法将利用田间温度、碳可获得性和微生物活动的差异。该分析方法将整合对复制子样本进行的多学科技术，并首次将下一代测序技术应用于这些海洋蛇纹岩流体。这项研究将从环境DNA、环境mRNA和单细胞基因组中产生广泛的序列数据，使我们能够识别代谢途径的原位表达和活性单细胞的基因组学。这些努力将与对这些流体中碳的彻底表征密切相关，这将侧重于确定可用的底物(例如甲烷、二氧化碳、有机酸)和表征反映特定代谢途径的生物标记物(例如脂质、氨基酸)。

The vast majority of deep seafloor sediments are inhabited by microbial communities that survive under extreme energy limitation, with apparent generation times of centuries to millennia. Hydrothermal systems are a stark contrast to these energy-starved environments and may represent important, high-activity, 'population centers' in the oceanic subsurface. When rocks from the Earth's mantle are uplifted and exposed to water, the resulting reactions lead to acidic fluids with high concentrations of hydrogen. Under certain circumstances, small organic molecules such as methane can also form in the absence of biology. These compounds can provide energy to subseafloor microbial communities and, given the ubiquity of mantle rocks, such reactions may fuel a significant proportion of the active subsurface biosphere. The current project will characterize the microbial communities inhabiting an iconic example of this type of system, the Lost City Hydrothermal Field, using a remotely operated vehicle. The ghostly spires of Lost City are highly telegenic and have been featured in professional documentaries. The high definition underwater video footage collected during the expedition will provide the raw material for an 8 week educational training program in digital media focused on kindergarten through 12th grade high school students and undergraduate students. The resulting short documentaries will be published on YouTube and the Utah Education Network.Mantle rocks comprise significant portions of the seafloor, and microbial communities hosted within them may be important mediators of carbon and energy exchange between the deep Earth and the surface biosphere. Upon tectonic uplift and exposure to water, the serpentinization of these materials releases potential energy in the form of hydrogen, methane, and heat, and further reaction of these products can sustain the abiogenic synthesis of small organic molecules. Recent studies have highlighted, however, the lack of alkalithermophiles that are capable of survival at the high pH (9-11) and elevated temperatures found in these systems. The almost complete lack of carbon dioxide (CO2) represents a second, and possibly more significant, limitation to growth. To better understand the extent of the serpentinite subsurface, this project will address the question: What limits biological activity in the serpentinite subsurface? Specifically, the proposed work will test the hypotheses: (1) microbial diversity spans a wider range of temperature-pH conditions than currently recognized and (2) the scarcity of CO2 is a key biological limitation to serpentinization-driven ecosystems that can be overcome by the metabolic activity of one or a few foundation species. These hypotheses will be tested during a 20 day (10 days on site) expedition to the Lost City Hydrothermal Field, focusing on fluids as windows to the subsurface biosphere. The sampling approach will capitalize on the differences in temperature, carbon availability, and microbial activity across the field. The analytical approach will integrate multidisciplinary techniques performed on replicate subsamples and feature the application of next-generation sequencing technologies to these marine serpentinizing fluids for the first time. This study will generate extensive sequence data from environmental DNA, environmental mRNA, and single-cell genomes, allowing us to identify the in situ expression of metabolic pathways and the genomics of active single cells. These efforts will be closely linked with a thorough characterization of carbon in these fluids that will focus on identifying available substrates (e.g. methane, CO2, organic acids) and on characterizing biomarkers that reflect specific metabolic pathways (e.g. lipids, amino acids).