Carbon Fixation Pathways in Marine Chemoautotrophic, Mesophilic Crenarchaeota: Implications for the Oceanic Carbon Cycle

知识价值。海洋的中深海和深海领域代表了地球上最大的连续栖息地，但我们对生活在这一区域的微生物种类以及它们的活动对全球的影响知之甚少。传统上，微生物在该区域的作用被视为有机物的降解者，同时释放二氧化碳。然而，最近这一观点受到了质疑，因为有研究发现，浮游绿原藻属于海洋绿原藻群1 (MG1)，在中深海和深海区主导原核细胞数量，实际上可能是自养的。然而，到目前为止，人们对这种广泛而多样的生物群体的代谢能力几乎一无所知。本项目旨在解决以下问题：。自养、嗜中温的绿原藻如何固定二氧化碳？是否存在通过硫化物或氢氧化获得能量的中温化化岩石自养绿藻？如果是，不同代谢组的自养碳固定途径是否不同？嗜温绿古藻和嗜热绿古藻对二氧化碳的固定有什么不同？这些差异能告诉我们古生菌进化的什么信息？这对我们对全球海洋碳固定和海洋碳循环的看法有什么影响？为了解决这些问题，研究人员建议首先阐明我们目前在培养和从各种环境中获得的氨氧化古菌所使用的碳固定途径。其次，他们建议在美国国家科学基金会资助的对东太平洋隆起9N热液喷口的研究巡航中，从营养线、氧最小带、热液羽流和热液喷口的一般附近获得分离物。目前的工作假设是，这些绿藻体内的自养碳固定不是通过卡尔文循环进行的，而是通过另一种二氧化碳固定途径进行的。如果这是真的，这将意味着海洋中大量的碳固定不是通过卡尔文循环进行的，这将导致我们重新考虑目前对海洋二氧化碳固定和海洋碳循环的看法。这项工作特别侧重于培养、分离和进一步表征这些生物，从而理想地补充了其他实验室正在进行的利用环境基因组技术的研究。更广泛的影响。这项工作解决了全球碳循环的一个重要但鲜为人知的方面，这是一个具有重要社会意义的话题。这项工作的结果将对完善目前的碳循环模型至关重要，并可能从根本上改变目前对碳在海洋中如何转移的看法。这个项目有多种教育组成部分，从当地学校的教学、本科生的参与到博士后的支持。预计结果将成为媒体采访（印刷和广播）的主题，并被整合到PI实验室或研究所现有的课程作业和网页中。

Intellectual merit. The meso- and bathypelagic realm of the oceans represents the largest continuous habitats on Earth, yet we know very little about the kind of microbes living in this zone and the global impact of their activities. Traditionally, the role of microbes in this zone has been seen as degraders of organic matter with a concomitant release of CO2. However, recently this perception has been called into question by the finding that planktonic Crenarchaeota belonging to the marine crenarchaeota group 1 (MG1), which dominate the prokaryotic cell numbers in the meso-and bathypelagic zone, could actually be autotrophs. However until now, almost nothing is known about the metabolic capacities of this extensive and probably diverse group of organisms. This project is designed to address the following questions:. How do autotrophic, mesophilic Crenarchaeota fix CO2?. Do mesophilic, chemolithoautotrophic Crenarchaeota exist that obtain energy through sulfide or hydrogen oxidation?. If yes, are there different autotrophic carbon fixation pathways in different metabolic groups?. What differences exist regarding CO2 fixation between mesophilic and thermophilic Crenarchaeota?. What can these differences tell us about the evolution of Archaea?. What are the consequences for our view of global oceanic carbon fixation and the oceanic carbon cycle in general?To address these questions, the investigators propose first to elucidate the carbon fixation pathway used by ammonium-oxidizing archaea that we have currently in culture and that have been obtained from a variety of environments. Secondly, they propose to obtain isolates from the nutricline, the oxygen minimum zone, hydrothermal plumes, and the general vicinity of hydrothermal vents during an already NSF-funded research cruise to the hydrothermal vents at 9N on the East Pacific Rise. The current working hypothesis is that autotrophic carbon fixation within these Crenarchaeota is not carried out via the Calvin cycle, but rather via an alternative CO2 fixation pathway. If true, this would mean that a significant amount of carbon fixation in the ocean is not carried out via the Calvin cycle, leading to a reconsideration of our current view of oceanic CO2 fixation and the oceanic carbon cycle in general. This work specifically focuses on cultivating, isolating and further characterizing these organisms and thus ideally complements ongoing research in other laboratories utilizing environmental genomic techniques. Broader impacts. This work addresses an important, yet poorly understood aspect of the global carbon cycle, a topic that has a significant societal relevance. Results of this work will be essential to refine current carbon cycle models, and potentially fundamentally alter the current view of how carbon is transferred in the ocean. This project has a variety of educational components ranging from teaching at local schools and the involvement of undergraduates to post-doctoral support. It is expected that results will be the topic of media interviews (print and radio) as well as be integrated into coursework and web-pages existing either in the PI's labs or at the institution.