From single pioneers to complex communities: Simultaneous discrimination of composition and inferring species interactions of fossil as well as modern pro- and eukaryotic microbial communities

该项目的目标是了解土壤中微生物群落的发展，从最初的组装到复杂的网络。微生物在极端环境中对土壤的发育有重要影响。土壤微生物群落结构对环境变化（如养分增加或温度升高）的强烈变化作出反应。南极土壤营养含量低，是脆弱的生态系统；它们被视为提供了非常好的环境变化的早期迹象。我们的中心工作假设包括原核微生物是在各种原核和真核微生物的复杂网络中初始组装成功的关键参与者，这些微生物基于网络中的不同功能负责进一步发展，并最终稳定土壤栖息地。考虑到氮源的生物有效性，真核藻类可能已经处于土壤发育的早期阶段。为了验证这些假设，该项目将把Göttingen大学和波茨坦GFZ的专业知识联系起来。我们将利用在南极洲东部Prydz湾Larsemann Hills无冰绿洲的冰川遗迹前田的五个样带收集的现有样本。深入分析土壤样品的关键理化参数是将微生物多样性与地球化学变量联系起来的关键。考虑到极端的贫营养环境和偏远的研究地点，我们预计将恢复相当数量的适应良好的迄今未知物种，代表潜在的生物技术应用的宝贵资源。我们将时间序列的时空替代方法扩展到微生物细胞外和细胞内DNA的微尺度比较。执行一种新的DNA提取协议将使灭绝（化石）和最近的活微生物群落之间的精确区分。这两个DNA库将在物种水平上对微生物群落进行分类评估。最后，通过深度测序（Illumina MiSeq），从两个互补和不同变量的rRNA基因特征扩增子将完成在物种水平上的分辨率。这对于高精度地推断促进早期土壤生态系统发展的物种相互作用至关重要，即在跨王国和领域的微生物关联中，例如真核藻类和细菌之间。功能基因分析将评估原核和真核微生物群落在碳和氮养分通量中的结构和功能关系。最后，在使用定量qPCR估计不同微生物和功能群的相对丰度后，可以推断出哪些物种相互作用对微生物生产起作用。

Goal of the project is an understanding of the development of microbial communities in soil, from the initial assembly to complex networks. Microorganisms critically impact the development of soils in extreme environments. Soil microbes react with strong shifts in their community structures on environmental changes, e.g. nutrient increase or temperature raise. Antarctic soils are fragile ecosystems due to their low nutrient content; they are seen to provide very good early indications of environmental change. Our central working hypothesis includes that prokaryotic microorganisms are the key players in the initial assembly succeeding in a complex network of the various pro- and eukaryotic microorganisms which based on different functions within the network is responsible for the further development and, finally, the stabilization of the soil habitat. Eukaryotic algae may interact as pioneers already in the early stages of soil development given the bioavailability of nitrogen sources. To test the hypotheses the project will link the expertise of Göttingen University and GFZ Potsdam. We will utilize already available samples collected at five transects in the forefields of glacier remains in ice-free oases at Larsemann Hills, Prydz Bay, East Antarctica. A thorough analysis of key physicochemical parameters of the soil samples is crucial to relate microbial diversity to geochemical variables. Given the extreme oligotrophic environment and remoteness of the study sites we expect to recover a considerable number of well adapted so far unknown species, representing a valuable source for potential biotechnological applications. We extend the space-for-time substitution approach of chronosequences to the microscale of comparisons between extracellular and intracellular DNA of microrganisms. Performing of a novel DNA extraction protocol will enable a precise distinction between extinct (fossil) and recent live microbial communities. Both DNA pools will serve the taxonomic assessment of microbial communities at the level of species. Finally, through deep sequencing (Illumina MiSeq) of amplicons from two complementary and differently variable rRNA gene signatures resolution at the species level will be accomplished. This is essential to infer those species interactions at high precision which facilitate the development of early soil ecosystems, i.e. within microbial associations across kingdoms and domains, e.g. between eukaryotic algae and bacteria. Analyses of functional genes will assess structure and functional relationships between pro- and eukaryotic microbial communities in nutrient fluxes of carbon and nitrogen. Finally, after estimating the relative abundances of the distinct microbial and functional groups using quantitative qPCR those species interactions can be inferred which act on the microbial production.