Recognition, signalling and response of the diatom Fragilariopsis to epibiotic bacterial colonization.

硅藻Fragilariopsis在南大洋的浮游植物中占主导地位，并在南极地区的重要（占全球15%）初级生产力中发挥核心作用。海洋初级生产是由微藻和细菌在空间上密切的相互作用推动的，并由它们对必需微量元素、微量和大量营养物质的相互需求驱动。最近对不同浮游植物物种的微生物组研究表明，它们拥有独特的微生物组，这些微生物组在浮游植物物种和时间尺度上是一致和特定的。然而，在不同的专业化水平上引起这些关联的机制过程却知之甚少。本文提出的主要假设是，尽管与硅藻的系统发育距离较远，但Fragilariopsis依赖或采用与动物和植物相似的识别和转导策略来应对环境细菌。因此，从理论上讲，这种类比允许将研究充分的动物和植物的免疫和微生物组科学的方法跨学科地转移到浮游植物物种。主动识别、选择和过滤过程的概念被认为引导了fragilariopopsis相关微生物组的组装，在多细胞生物的免疫背景下，甚至在多细胞海洋大型藻类中，但在硅藻中却没有得到很好的理解。这些反应是通过受体介导的对细菌激发子的识别和经过充分研究的信号级联反应（例如通过一氧化氮（NO））触发的。因此，这会导致各种可量化的应激标记上调，如细胞内活性氧或谷胱甘肽与谷胱甘肽二硫比的变化。在一定程度上，这些应激标记物已经在微藻中得到了验证，并且海洋硅藻中NO信号和NO合成酶样基因序列的第一个证据正在出现。因此，该提案解决了相关的DFG - SPP问题，例如需要“提高对极地过程和机制的理解”和“[SO生物]对环境变化的反应”。具体地说，我们将从Fragilariopsis微生物组中分离、培养和鉴定各种细菌。同时，不同的Fragilariopsis生态型被灭绝。在共培养试验中，我们将使用已知的和完善的化学和分子工具来表征和量化脆弱毛孢对细菌和细菌分子激发子（如细菌脂多糖）的细胞内和细胞外反应。本提案的短期目标是证实脆弱蒿对细菌或细菌信号分子的积极反应。这项工作的长期目标是通过实验调整未来SO气候制度来分析全息生物组装和挑战识别过程，以了解Fragilariopsis holobiont对预测气候变化情景的敏感性。

The diatom Fragilariopsis dominates phytoplankton in the Southern Ocean and plays a central role in the significant (15% of global) primary productivity of Antarctic regions. Marine primary production is fuelled by spatially close interactions between microalgae and bacteria and driven by their reciprocal needs for essential trace elements, micro- and macro-nutrients. Several recent microbiome studies of diverse phytoplankton species suggest that they harbour unique microbiomes, which are consistent and specific within phytoplankton species and across temporal scales. Yet, the mechanistic processes causing these associations at different levels of specialization are poorly understood.The main hypothesis addressed in this proposal postulates that Fragilariopsis relies on, or employs comparable recognition and transduction strategies in response to environmental bacteria as animals and plants, despite their phylogenetic distance to the diatom. Thus, in theory this analogy allows a cross-disciplinary transfer of methodology from well investigated immunity and microbiome science in animals and plants to a phytoplankton species.The concept of active recognition, selection and filtering processes, which supposedly steer the assembly of Fragilariopsis-associated microbiomes, is well understood in the context of immunity in multicellular organisms, even in multicellular marine macroalgae, but not in diatoms. Such responses are triggered via receptor-mediated recognition of bacterial elicitors and mediated by well-investigated signaling cascades (e.g. via nitric oxide (NO)). As a consequence, this leads to the upregulation of a variety of quantifiable stress markers, such as intracellular reactive oxygen species or a shift of the glutathione to glutathione-disulfide ratio. Partially, these stress markers have been verified in microalgae and first evidence of NO signaling and NO synthase-like gene sequences in marine diatoms is emerging. This proposal thus addresses pertinent DFG SPP questions, such as the need of “improved understanding of polar processes and mechanisms'' and the “response [of SO organisms] to environmental change”. Specifically, we will isolate, culture and identify various bacteria from Fragilariopsis microbiomes. In parallel, different Fragilariopsis ecotypes are axenified. In co-culture assays, we will employ known and well established chemical and molecular tools to characterize and quantify intra- and extracellular responses of Fragilariopsis to bacteria and bacterial molecular elicitors, such as bacterial lipopolysaccharides.The short term goal of this proposal is to corroborate an active response of Fragilariopsis to bacteria or bacterial signaling molecules. The long-term goal of this work is to analyse the holobiont assembly and challenge the recognition process by experimentally adjusting future SO climate regimes to understand the susceptibility of the Fragilariopsis holobiont to predicted climate change scenarios.