Impact of soil microaggregate characteristics on microbial colonization patterns

拟议的研究单位FOR2179旨在深入了解土壤微团聚体的形成过程和稳定性与其化学成分和微结构的关系，以及微团聚体对土壤功能的作用，包括微生物的栖息地功能。微团聚体和粘土颗粒是土壤中细菌的主要栖息地。因此，土壤成分向三维结构的排列和聚集是生物过程的控制因素之一。微生物对土壤微团聚体的形成、稳定和失稳具有重要作用。这一分项目中提出的工作涵盖两个方面，即细菌微团聚体的栖息地功能以及细菌在微团聚体形成和稳定性中的作用。我们将证明这样一个假设，即从不同粘土含量的土壤拓扑序列中获得的不同类型的微团聚体拥有不同类型的细菌群落，并且这种选择受到微团聚体的物理化学特征的影响。为此，将使用分子方法分析分级微聚集体中的细菌群落组成和多样性。所获得的描述微生物群落的数据将结合描述微团聚体的物理化学参数的数据进行分析，这些参数将由本研究单位的不同合作伙伴提供，以确定对细菌定植产生影响的那些因素。这一分项目的第二个主要目标将是研究代谢活性细胞的定位，由此预计不同的细菌分类群将活跃在空间受限的微聚集体的特定微站点中。将在荧光显微镜的基础上结合LA-IRMS、LA-ICP-MS和NanSIMS等质谱学方法，在微米尺度上分析这些微区的特征，从而在单细胞水平上进行分析。将比较活跃和非活跃细胞的栖息地，以确定微团聚体内和微团聚体上微生物活动的可能控制。为了评估细菌在聚集体形成中的作用，我们将在项目的第一阶段集中于选定的模式生物，并进行聚集实验，以确定不同的细菌对聚集体形成和稳定的贡献程度。将通过研究标记的胞外聚合物的降解来分析微聚体的微生物不稳定，这些聚合物在中央微观世界实验中作为稳定的有机物质。通过这些不同的方法，我们将获得数据，一方面可以更深入地了解微生物如何影响微团聚体的形成和解聚，另一方面微团聚体对微生物存在和活动的调节机制。

The proposed research unit FOR2179 aims at an in-depth understanding of the process of soil microaggregate formation and microaggregate stability in relation to its chemical composition and microarchitecture, and the role of microaggregates for soil functioning, including the habitat function for microorganisms. Microaggregates and clay particles represent a major habitat for bacteria in soil. The arrangement and aggregation of soil components to a three dimensional structure is thus among the controlling factors of biological processes. Microorganisms contribute to the formation, stability and destabilization of soil microaggregates. The work proposed within this subproject covers both aspects, the habitat function of microaggregates for bacteria and the role of bacteria in microaggregate formation and stability. We will prove the hypothesis that different types of microaggregates, obtained from a soil toposequence of variable clay content, host different types of bacterial communities and that this selection is influenced by the physicochemical characteristics of the microaggregates. To this end, bacterial community composition and diversity will be analysed in fractionated microaggregates using molecular methods. The obtained data that describe the microbial communities will be analysed in combination with those that describe the physicochemical parameters of the microaggregates, which will be provided by different partners of this research unit, to identify those factors that exert an effect on bacterial colonization. A second major aim of this subproject will be the study of the localization of metabolically active cells, whereby different bacterial taxa are expected to be active in spatially restricted specific microsites of microaggregates. The characteristics of these microsites will be analysed at micrometre scale and thus single-cell-level, based on fluorescent microscopy in combination with mass spectrometric methods such as LA-IRMS, LA-ICP-MS and nanoSIMS. The habitats of active and inactive cells will be compared to identify possible controls of microbial activity in and on microaggregates. To assess the role of bacteria for aggregate formation, we will focus on selected model organisms in this first phase of the project and perform aggregation experiments to identify to what extent different bacteria contribute to aggregate formation and stabilization. Microbial destabilization of microaggregates will be analysed by studying the degradation of labelled extracellular polymeric substances, which serve as stabilizing organic material in a central microcosm experiment. With these different approaches, we will obtain data that allow to obtain a deeper understanding regarding the question how microorganisms affect microaggregate formation and their disaggregation on the one hand and the regulatory mechanisms of microaggregates on microbial presence and activity on the other hand.