Molecular requirements of Bacillus subtilis root colonization

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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.