Tracing the food chain from magnetotactic bacteria to protozoa under laboratory and environmental conditions

趋磁细菌（MTB）产生的化石磁小体是古地磁学研究中的重要替代物，用于重建地球历史上过去地质事件的时间。 然而，控制MTB在自然环境中丰度的环境和生态过程及其磁小体知之甚少。 MTB生态学的一个关键方面仍然缺乏特征，是它们在自然环境中的丰度如何由微生物捕食者控制：捕食性原生动物（原生生物）。 我们将测试周围的假设是否原生动物放牧起着控制MTB丰度的性质和原生动物放牧对磁小体保存的影响。 我建议通过应用一种新的实验装置来解决这一挑战，该装置将首次直接识别在环境条件下消耗MTB的原生生物的全部多样性，并在受控的实验室条件下揭示MTB放牧和磁小体溶解的速率。 我的实验室开发了一种新的实验装置，可以识别原生生物对同位素标记的猎物细胞的摄食，我们将应用于自然环境设置，以揭示海洋和淡水环境中捕食MTB的原生生物的多样性。 使用控制实验室设置与缺氧-缺氧梯度，我们将进行原生动物放牧实验与突变体和野生型MTB，以确定MTB的表型发挥作用，帮助MTB逃脱捕食某些原生生物。 这将与Dirk Schüler教授（拜罗伊特大学）合作完成，他保存了大量具有不同表型的突变MTB菌株的培养物，我们将在我们的原生动物放牧实验中应用这些菌株。 这将揭示MTB的表型是关键的生存在关键的原生动物捕食者的存在，以及他们如何避免捕食在某些环境条件下。 我们还将评估原生生物的磁小体溶解速率，其可以在摄入MTB后溶解磁小体。 对于那些被摄入但未完全溶解的磁小体，我们将评估磁小体形态和磁性的变化。 将与Stuart Gilder教授博士（LMU慕尼黑）合作，通过在放牧实验结束时对摄入的磁小体进行一阶反转曲线（FORC）分析，研究摄入的磁小体的磁性改变。 这将揭示原生动物的掠食如何影响磁小体的磁性，磁小体的磁性化过程中的一个重要但知之甚少的因素。 由于MTB产生的磁小体是过去地质事件的古地磁研究中使用的重要替代物，因此该项目的结果将有助于解释地质记录中的磁化石。

Fossilized magnetosomes produced by magnetotactic bacteria (MTB) are a crucial proxy in paleomagnetism studies, that are used to reconstruct the timing of past geological events in Earth history. However, the environmental and ecological processes controlling the abundance of MTB in natural environments, and their magnetosomes, are poorly understood. One key aspect of MTB ecology that remains poorly characterized, is how their abundance in natural environments is controlled by microbial predators: predatory protozoa (protists). We will test hypotheses surrounding whether protist grazing plays a role in controlling MTB abundance in nature and the effects of protist grazing on the preservation of magneotosomes. I propose to address this challenge by applying a novel experimental setup that will, for the first time, directly identify the full diversity of protists that consume MTB under environmental conditions and reveal rates of MTB grazing and magnetosome dissolution under controlled laboratory conditions. My lab has developed a new experimental setup that allows for identification of protist grazing on isotopically labeled prey cells, that we will apply to natural environmental settings to reveal the diversity of protists that prey on MTB in both marine and freshwater environments. Using a controlled laboratory setup with an oxic-anoxic gradient, we will perform protist grazing experiments with mutant and wild-type MTB to identify which MTB phenotypes play a role in helping the MTB escape predation by certain protists. This will be done in collaboration with Prof. Dr. Dirk Schüler (University of Bayreuth) who maintains a large culture collection of mutant MTB strains with varying phenotypes, that we will apply in our protist grazing experiments. This will reveal the MTB phenotypes that are critical for their survival in the presence of key protist predators, and how they avoid predation under certain environmental conditions. We will also assess rates of magnetosome dissolution by the protists, that can dissolve the magnetosomes after the MTB have been ingested. For those magnetosomes that are ingested, but not completely dissolved, we will assess the changes in magnetosome morphology and magnetic properties. Altered magnetic properties of ingested magnetosomes will be studied in collaboration with Prof. Dr. Stuart Gilder (LMU Munich), by means of first order reversal curve (FORC) analysis of ingested magnetosomes at the end of the grazing experiments. This will reveal how protist grazing effects the magnetic properties of the magnetosomes, an important but poorly understood factor in the magnetosome fossilization process. Because the magnetosomes produced by MTB are a crucial proxy used in paleomagnetism studies of past geological events, the results of this project will aid the interpretation of magnetofossils in the geological record.