Host-microbe systems in the ocean: identifying genetic determinants of Phaeobacter inhibens pathogenesis of the phytoplankton Emiliania huxleyi

海洋中的宿主微生物系统：识别浮游植物赫胥黎浮游植物抑制褐杆菌发病机制的遗传决定因素

• 批准号: RGPIN-2018-05706
• 负责人: Case, Rebecca
• 金额: $ 2.62万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=646948
• 关键词: Host; microbe; systems; ocean; identifying

Microbes dominate marine habitats and these invisible life forms are responsible for driving the biogeochemical cycles that sustain life on our planet. Perhaps most important are phytoplankton, as these microalgae perform half of the photosynthesis on earth, removing carbon dioxide from the atmosphere and generating oxygen. One ubiquitous and abundant of these is Emiliania huxleyi, which can form blooms in the oceans as large as countries. Besides fixing carbon through photosynthesis, it can also mineralize it into calcite disks that cover its surface. These fall to the bottom of the ocean when the microalgae dies, where they can stay for over 50,000 years. E. huxleyi is also unique in that it uses biologically produced molecules to interact with higher (fish and birds) and lower (protist grazers and viruses) tropic levels within the marine food web. We have recently identified that E. huxleyi also closely interacts with bacteria, which can be pathogenic on their host and thereby accelerate release of calcite. One such bacterium, Phaeobacter inhibens, kills E. huxleyi by activating its programmed cell death pathway (PCD) through an effector molecule delivered through its type IV secretion system (T4SS). Viruses are also known to activate its PCD pathway and this cell lysis is a critical step in the microbial loop. We are the first group to show bacteria also occupy this niche. By sequencing all the RNA transcripts of P. inhibens genes (transcriptomics) when it is killing E. huxleyi, we aim to discover genes involved in bacterial pathogenesis of phytoplankton. We will then perform fitness experiments where a library of >200,000 mutants (RB-TnSeq) will be applied to their host, E. huxleyi, and those which are under and over represented during pathogenesis can be identified as fitness determinants. We will also use this mutant library to further characterize the genetic networks and pathways identified from the transcriptomics and RB-TnSeq in this pathogenic niche. This research proposal will elucidate how this novel pathogen targets E. huxleyi and will allow us to be the first to identify the genetic determinants of a phytoplankton pathogen.

微生物主导着海洋栖息地，这些看不见的生命形式负责推动维持地球生命的生物地球化学循环。也许最重要的是浮游植物，因为这些微藻完成了地球上一半的光合作用，从大气中去除二氧化碳并产生氧气。其中一种无处不在且数量众多的是赫胥黎菌，它可以在像国家一样大的海洋中形成水华。除了通过光合作用固定碳外，它还可以将其矿化成覆盖其表面的方解石盘。当微藻死亡时，它们会落到海底，在那里停留超过5万年。赫胥黎线虫的独特之处在于，它利用生物产生的分子与海洋食物网中热带水平较高的（鱼类和鸟类）和较低的（原生食草动物和病毒）相互作用。我们最近发现赫胥黎杆菌也与细菌密切相互作用，这些细菌可以对宿主致病，从而加速方解石的释放。其中一种细菌，Phaeobacter inhibens，通过通过IV型分泌系统（T4SS）传递的效应分子激活其程序性细胞死亡途径（PCD）来杀死赫胥黎e.h。已知病毒也激活其PCD途径，这种细胞裂解是微生物循环的关键步骤。我们是第一个发现细菌也占据这个生态位的团队。通过对P. inhibens杀死e.h xleyi时所有基因的RNA转录本（转录组学）测序，我们旨在发现浮游植物细菌致病的相关基因。然后，我们将进行适应度实验，其中bbb200,000个突变体（RB-TnSeq）库将应用于它们的宿主E. huxleyi，那些在发病过程中代表性不足和代表性过高的突变体可以被确定为适应度决定因素。我们还将使用这个突变文库进一步表征从转录组学和RB-TnSeq中鉴定出的遗传网络和途径。这项研究计划将阐明这种新型病原体是如何靶向赫胥黎大肠杆菌的，并将使我们成为第一个确定浮游植物病原体遗传决定因素的人。