Molecular requirements of Bacillus subtilis root colonization

在土壤中，植物的根与大量的细菌生活在一起。其中一些为植物提供有益的活动，以交换根部分泌的营养物质。这些细菌可以通过调节植物的新陈代谢和对抗病原体来显著促进植物的生长和健康。有益微生物开始在世界范围内被用作生物肥料和生物农药，并构成了化学肥料和农药的一个非常有趣和可持续的替代品。虽然以细菌为基础的肥料很有前途，但仍有很大的改进空间。然而，目前缺乏关于这些微生物如何接近和定植根部的基本知识，这大大减缓了生物肥料使用和配方的改进。我的研究项目旨在研究农业中使用的枯草芽孢杆菌是如何在根部定植的。在我们的第一个目标中，我们将探索植物如何将枯草芽孢杆菌吸引到其根部，以及在这一过程中涉及的细胞机制和分子。此外，我们将确定植物及其生长阶段，特别有效地吸引枯草芽孢杆菌。这些试验的结果将通过指出哪些条件有利于枯草芽孢杆菌吸引到根部，为优化以枯草芽孢杆菌为基础的生物肥料在田间的使用提供有用的指导。在我们的第二个目标中，我们想要了解植物根系刺激枯草芽孢杆菌多细胞群落形成的机制，称为生物膜，在其表面。我最近展示了存在于根细胞外的糖成分刺激枯草芽孢杆菌生物膜的形成。虽然这一发现在细菌与植物相互作用的研究领域具有重要影响，但其细胞机制仍不清楚。我们将进一步探索这一现象，为枯草芽孢杆菌在根系上建立强大群落的机制提供新的见解。此外，生物膜的形成是细菌普遍存在的特征，尤其是人类病原体，是临床环境中的一个重要问题。通过详细研究细菌生物膜在活的和变化的表面（即根）上的形成，我的研究小组将增加我们对多细胞宿主存在时形成的生物膜的理解。这些信息将是非常重要的，特别是在摆脱医院出生的持续性感染，这往往是通过生物膜形成维持。本研究计划的第三个目标是鉴定新的枯草芽孢杆菌基因和与根建立强大相互作用所需的分子过程。这些信息将为我们提供更有效的工具来分离新的和更有效的生物肥料细菌，并设计具有更活跃的根关联途径的有益菌株。综上所述，该项目将对加拿大和国际上细菌-植物相互作用和生物膜形成研究领域的基础研究和应用研究产生许多积极影响。这项研究将产生涉及细菌生物膜的跨界相互作用的基础知识，这应该可以转化为医院环境中存在的许多病原体。此外，它还将在优化枯草芽孢杆菌作为生物肥料的使用和开发更有效的生物肥料方面具有直接的应用价值。

In the soil, plant roots live in association with an important amount of bacteria. Some of them provide beneficial activities for the plant in exchange of the nutrients secreted by the root. These bacteria can notably promote plant growth and health by modulating its metabolism and by fighting pathogens. Beneficial microbes are starting to be used as biofertilizers and biopesticides worldwide, and constitute a very interesting and sustainable alternative to chemicals fertilizers and pesticides. While bacterial-based fertilizers are promising, much room is available to improve them. However, the current lack of fundamental knowledge on how these microbes approach and colonize the roots considerably slows down the improvement of biofertilizers’ usage and formulation. My research project proposes to establish how the spore-forming bacterium B. subtilis, used in agriculture, colonizes the root. In our first objective, we will explore how the plants attract B. subtilis toward its root, and what are the cellular mechanisms and molecules involved in this process. Also, we will identify the plants and their growth stage that are particularly potent in attracting B. subtilis. Results from these experiments will provide useful guidelines to optimize usage of B. subtilis – based biofertilizers in the field, by indicating which conditions will favor B. subtilis attraction toward the roots. In our second objective, we want to understand the mechanisms by which the plant roots stimulates formation of B. subtilis multicellular communities, termed biofilms, on its surface. I recently showed that the sugars constitutively present outside the roots’ cells stimulate B. subtilis biofilm formation. While this discovery had important impacts in the field of research on bacterial-plant interaction, the cellular mechanisms involved are still unknown. We will further explore this phenomenon to provide novel insights on the mechanisms by which B. subtilis establish a robust community on roots. Additionally, biofilms formation is a ubiquitous feature of bacteria, notably human pathogens, and is an important concern in clinical settings. By examining in detail bacterial biofilm formation on the living and changing surface that is the root, my research group will increase our comprehension of the biofilms formed in presence of a multicellular host. These informations will be of great importance notably in getting rid of hospital-born persistent infections, which often is maintained via biofilm formation. The third objective of this research program aim at identifying novel B. subtilis genes and molecular processes required for establishing a robust interaction with the root. These information will give us more potent tools to isolate new and more efficient biofertilizers bacteria and to engineer beneficial strains with more active root-association pathways. In summary, this proposed project will have many positive impacts on fundamental and applied research in the research field of bacterial-plant interaction and biofilm formation both at the canadian and international levels. This research will generate fundamental knowledge on cross-kingdom interactions involving bacterial biofilms, which should be translatable to many pathogens present in hospital settings. Additionally, it will also have immediate applications in optimizing our usage of B. subtilis as a biofertilizer and in potentially developing more potent biofertilizers.