Metabolic activity of planktonic archaea and their contribution to the marine carbon cycle

海洋覆盖了地球的四分之三，平均水深4000米，是世界上S最大的生命栖息地之一。在过去的二十年里，很明显，古生界的微生物丰富，海洋微微浮游生物的所有深度都是与生态有关的成员。最丰富的海洋古生物种群的化学自养生活方式源于在纯养殖中的成功培养。到目前为止，这一新门的所有成员都是通过将氨好氧转化为亚硝酸盐并将二氧化碳固定为主要碳源来产生能量的。海洋氨氧化古菌表现出极高的底物亲和力，并运行最高效的有氧二氧化碳固定途径，非常适合在营养不良的环境中茁壮成长，就像大多数海水的典型情况一样。氨氧化古生菌由于其生理特性和高丰度，已被公认为海洋中的优势硝化细菌和重要的初级生产菌。基于其无处不在的分布，我假设最近描述的羟基海酸/羟丁酸循环(HP/HB循环)的古细菌变体是光带以下海洋黑暗领域最重要的CO2固定途径。以前对中上层营养化学通量进行量化的模型大多基于过时的假设，即细菌而不是古生菌是主要贡献者。因此，这里提出的研究项目旨在利用新的生物特异性分析工具重新评估浮游古细菌对海洋C循环和中上层化学自养的贡献。例如，苏云金杆菌氨氧化剂的现场活性和周转率将通过测量稳定的C和H同位素掺入诊断苏云金芽胞菌脂类中来确定。结合编码苏门氏菌Hp/Hb循环的新标记基因的分布和NanoSIMS/His-SIMS技术的应用，我们将调查化石型自养古菌对远洋初级生产力的实际贡献。此外，我建议在接近环境的条件下培养尚未确定特征的深海Thaumarocota分支的成员，以获得它们的生理和遗传特征。总之，本研究项目旨在获得关于世界上S最丰富的生物群之一的生物学方面的新发现，并为海洋C循环的生物地球化学理解做出贡献。

The oceans cover about three quarters of the Earth and the water colmn, with an average depth of 4000m, represents one of the World s largest habitate for life. Over the last two decades it has became evident that microorganisms of the domain Archaea are abundant and ecological relevant members of the oceanic picoplankton in all depth. The chemolithoautotrophic life style of the most abundant marine archaeal group derived from the successful cultivation in pure culture. By date all members of this novel phylum Thaumarchaeota generate energy by the aerobic conversion of ammonia to nitrite and fix CO2 as primary carbon source. Exhibiting extremely high subtrate affinity and operating the most energy-efficient aerobic CO2 fixation pathway, marine ammonia-oxidizing archaea are perfectly suited to thrive in nutrient-poor environments as typically for most of the ocean water. Because of their physiology and high abundance ammonia-oxidizing archaea have been recognized as predominant nitrifyers and important primary produzers in the Ocean. Based on its ubiquitous distribution I hypothesis that the recently characterized thaumarchaeal variant of the hydroxypionate/hydroxybutyrate cycle (HP/HB cycle) is the most important CO2 fixation pathway in the dark realm of the ocean below the photic zone. Previous modells quantifying the pelagic chemoautrotrophy flux are mostly based on the out-dated assumption that bacterial and not archaeal nitrifyers are the main contributors. Hence, the research project proposed here aims to re-evaluate the contribution of planktonic archaea to the marine C-cycle and to pelagic chemoautotrophy using novel, organism specific analytical tools. For instance, the in situ activity and turn over rates of thaumarchaeal ammonia oxidizers will be determined by measuring the incorporation of stable C and H isotopes into diagnostic thaumarchaeal lipids. In combination with the distribution of novel marker genes coding for the thaumarchaeal HP/HB cycle and application of the NanoSIMS/HIS-SIMS technology we will investigate the actual contribution of chemolithoautotrophic archaea to the pelagic primary production. Furthermore, I propose to cultivate members of the yet uncharacterized deep sea thaumarchaeota clade at near-environmental conditions to get access to their physiological and genetic characteristics. In sum, this research project aims to obtain novel findings on the biology of one of the World s most abundant organism group and to contribute to the biogeochemical understanding of the marine C-cycle.