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。它们中的一些为植物提供有益的活动，以交换根分泌的营养。这些细菌通过调节新陈代谢和对抗病原体，可以显著促进植物的生长和健康。有益的微生物正开始在世界范围内用作生物肥料和生物杀虫剂，并构成了一种非常有趣和可持续的化学品、肥料和杀虫剂的替代品。尽管细菌基肥料前景看好，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根部并在根部定居的基础知识，大大减缓了生物肥料使用和配方的改进。我的研究项目建议确定用于农业的芽胞形成细菌B.subtilis是如何在根上定植的。在我们的第一个目标中，我们将探索植物如何将枯草杆菌吸引到它的根部，以及这个过程中涉及的细胞机制和分子是什么。此外，我们还将确定在吸引枯草杆菌方面特别有效的植物及其生长阶段。这些试验的结果将通过指示哪些条件有利于枯草杆菌向根部吸引，为优化田间枯草杆菌生物肥料的使用提供有用的指导方针。在我们的第二个目标中，我们想要了解植物根刺激枯草杆菌多细胞群落在其表面形成生物膜的机制。我最近发现，根细胞外的糖会刺激枯草杆菌生物膜的形成。虽然这一发现对细菌-植物相互作用的研究领域产生了重要影响，但其中涉及的细胞机制仍不清楚。我们将进一步探索这一现象，为枯草杆菌在根上建立一个强大的群落的机制提供新的见解。此外，生物膜的形成是细菌，特别是人类病原体的一个普遍特征，也是临床环境中的一个重要问题。通过详细研究活的和变化的表面即根的细菌生物膜的形成，我的研究小组将增加我们对在多细胞宿主存在下形成的生物膜的理解。这些信息将对消除医院出生的持续性感染非常重要，医院出生的持续性感染通常是通过生物膜形成来维持的。这项研究计划的第三个目标旨在鉴定新的枯草杆菌基因和分子过程，这些基因和分子过程是建立与根的强大相互作用所必需的。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联合途径的有益菌株。总之，这一拟议的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王国相互作用的基础知识，这些知识应该可以翻译成医院环境中存在的许多病原体。此外，它还将立即应用于优化枯草杆菌作为生物肥料的使用，并潜在地开发更有效的生物肥料。

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.