Collaborative Research: Environmental Drivers of Chemoautotrophic Carbon Production at Deep-Sea Hydrothermal Vents - Comparative Roles of Oxygen and Nitrate

1977年首次发现的深海热液喷口是微生物化学合成而不是光合作用成为有机碳主要来源的典型生态系统。化学合成微生物利用氧化排气流体中含有的还原无机化学物质（如硫化氢或氢气）所产生的能量，将二氧化碳（CO2）转化为细胞物质。通过这样做，它们有效地将地热资源的能量转移到更高的营养水平，在这个过程中支持独特而迷人的生态系统，这些生态系统以高生产力为特征——在贫瘠的深海景观中形成绿洲。虽然这些生态系统功能的一般观点已经建立，但我们对这些系统的微生物学和生物地球化学的理解仍然存在重大差距。特别缺乏的是测量就地微生物活动率的研究，而这些研究最终需要了解这些生态系统的生产并评估它们对全球生物地球化学循环的影响。该项目利用了最近开发并在现场进行了测试的微型机器人实验室——通气潜水孵化装置（Vent-SID）。该仪器首次使测定在原位压力和温度下的碳固定速率成为可能，彻底改变了我们在深海热液喷口进行微生物生物地球化学调查的方式。这是两个美国和外国机构之间的跨学科合作努力，为建立网络和促进国际合作创造了独特的机会。这也将使参与该项目的两名研究生受益，他们将接触到广泛的仪器和科学领域，促进他们的跨学科教育。与Sage School的学术院长Nitzan Resnick博士合作，将开发一项小学推广计划，并与学校建立长期合作伙伴关系。此外，将设立一个邮轮博客网站，向学校和更广泛的公众传播研究结果。其结果将成为媒体报道的主题，并将整合到PI实验室或机构现有的课程作业和网页中。该项目使用最近开发的微型机器人实验室Vent-SID来测量化学自养生产的速率，并确定氧气和硝酸盐在驱动深海热液喷口在原位压力和温度下的化学合成中的相对重要性，并解决以下目前尚未解决的科学目标：1)获得原位化学自养碳固定速率，2)获得原位硝酸盐还原速率测量值，3)将这些过程的测量值与参与碳和能量代谢的关键基因的表达直接关联。虽然最近的数据表明硝酸盐还原成N2（反硝化）或NH4+（硝酸盐异化还原为铵）可能是化学自养生产的重要组成部分，但在热液喷口的原位测量中从未测量过no3还原速率。研究人员推测，化学自养生长与排气口微生物群落的硝酸盐呼吸密切相关。在项目进行约12个月的巡航期间（至2017年2月），研究人员将在东太平洋隆起的9°46N至9°53N段进行总共4次Vent-SID部署以及辅助采样收集。他们将集中精力在两个扩散流喷口，“螃蟹温泉”和“泰迪熊”。“螃蟹温泉”是一个漫流喷口（温度：25°C），已被用作模型系统，以深入了解化学自养过程，并在过去几年中经常进行采样。从地球化学和微生物学的角度来看，该喷发点的特征都很好，为提出的过程导向研究提供了很好的背景数据。“泰迪熊”是2014年1月发现的扩散流站点，它的温度较低（T: 12°C），是一个很好的比较站点。研究人员将进行一些短时间的时间过程孵育，以评估不同环境参数的作用，这些参数已被确定为可能的关键变量（例如，O2，温度，NO3-），并使用亚转录组学分析将这些过程速率测量与功能基因的表达联系起来。这项研究将首次尝试测量热液喷口微生物组合在临界原位条件下的关键代谢过程，并评估原位电子供体和受体途径的定量重要性。在未来，预计vent - sid将成为海洋学界测量热液喷口在原位压力和喷口流体温度下相关代谢过程时间序列速率的常规应用。

Deep-sea hydrothermal vents, first discovered in 1977, are exemplary ecosystems where microbial chemosynthesis rather than photosynthesis is the primary source of organic carbon. Chemosynthetic microorganisms use the energy generated by oxidizing reduced inorganic chemicals contained in the vent fluids, like hydrogen sulfide or hydrogen gas, to convert carbon dioxide (CO2) into cell material. By doing so, they effectively transfer the energy from a geothermal source to higher trophic levels, in the process supporting the unique and fascinating ecosystems that are characterized by high productivity - oases in the otherwise barren deep ocean landscape. While the general view of the functioning of these ecosystems is established, there are still major gaps in our understanding of the microbiology and biogeochemistry of these systems. Particularly lacking are studies measuring rates of microbial activity in situ, which is ultimately needed to understand production of these ecosystems and to assess their impact on global biogeochemical cycles. This project makes use of the Vent-Submersible Incubation Device (Vent-SID), a robotic micro-laboratory that was recently developed and tested in the field. This instrument makes it possible for the first time to determine rates of carbon fixation at both in situ pressures and temperatures, revolutionizing the way we conduct microbial biogeochemical investigations at deep-sea hydrothermal vents. This is an interdisciplinary and collaborative effort between two US and foreign institutions, creating unique opportunities for networking and to foster international collaborations. This will also benefit two graduate students working in the project, who will get exposed to a wide range of instrumentation and scientific fields, facilitating their interdisciplinary education. In collaboration with Dr. Nitzan Resnick, academic dean of The Sage School, an elementary school outreach program will be developed and a long-term partnership with the school established. Further, a cruise blog site to disseminate the research to schools and the broader public will be set up. The results will be the topic of media coverage as well as be integrated into coursework and webpages existing either in the PI's labs or at the institution.This project is using a recently developed robotic micro-laboratory, the Vent-SID, to measure rates of chemoautotrophic production and to determine the relative importance of oxygen and nitrate in driving chemosynthesis at deep-sea hydrothermal vents at in situ pressures and temperatures and to tackle the following currently unresolved science objectives: 1) obtain in situ rates of chemoautotrophic carbon fixation, 2) obtain in situ nitrate reduction rate measurements, and 3) directly correlate the measurement of these processes with the expression of key genes involved in carbon and energy metabolism. Although recent data suggests that nitrate reduction either to N2 (denitrification) or to NH4+ (dissimilatory reduction of nitrate to ammonium) might be responsible for a significant fraction of chemoautotrophic production, NO3-reduction rates have never been measured in situ at hydrothermal vents. The researchers hypothesize that chemoautrophic growth is strongly coupled to nitrate respiration in vent microbial communities. During a cruise that will take place approximately 12 months into the project (~Feb 2017), the researchers will carry out a total of 4 deployments of the Vent-SID as well as ancillary sampling collection at the 9°46N to 9°53N segment of the East Pacific Rise. They will focus efforts on two diffuse-flow vent sites, "Crab Spa" and "Teddy Bear". "Crab Spa" is a diffuse flow vent site (T: 25°C) that has been used as a model system to gain insights into chemoautotrophic processes and has been frequently sampled over the last several years. This vent site has been very well characterized, both geochemically and microbiologically, providing excellent background data for the proposed process oriented studies. "Teddy Bear" is a diffuse-flow site that was discovered in Jan 2014, and it has a lower temperature (T: 12°C), making it a good comparative site. The researchers will perform a number of short duration time-course incubations to assess the role of different environmental parameters that have been identified as likely key variables (e.g., O2, temperature, NO3-), and to link these process rate measurements to the expression of functional genes using metatranscriptomic analyses. This study will be the first attempt to measure critical metabolic processes of hydrothermal vent microbial assemblages under critical in situ conditions and to assess the quantitative importance of electron donor and acceptor pathways in situ. In the future, it is envisioned that the Vent-SID will become a routine application by the oceanographic community for measuring time series rates of relevant metabolic processes at hydrothermal vents under in situ pressures and vent fluid temperatures.