BIORELAX

The rhizosphere microbiota plays a crucial role in plant growth and health. They can mitigate stresses like water deficit, which is frequent due to climate change. By producing hormones and retaining water/nutrients through biofilms, these microbes can alleviate drought stress. However, the microbial mechanisms influencing soil properties remain vague. Previously, we obtained a rhizosphere microbiota enhancing Brassica juncea growth under water deficit conditions. An increased biofilm production by this community was demonstrated in vitro, but we could not verify the precise mechanisms in situ. This project aims to show if this community alters soil properties to promote plant growth during drought. We will leverage state-of-the-art technologies available in local platforms at UMR Agroécologie and PAM: i) High-throughput plant phenotyping based on picture analysis (4PMI platform), ii) Scanning Electron Microscopy to visualize microbial cells and biofilms (DIMACELL platform), iii) Soil metabolomics to detect metabolites produced by plants and microbes (DIVVA platform), and iv) Nuclear Magnetic Resonance relaxometry to non-invasively assess water mobility and distribution in soil aggregates (DIVVA platform). We will grow plants in sterile soil inoculated with live or inactivated (autoclaved) rhizosphere microbiota, either evolved for biofilm production or not, and subjected to varying water deficit regimes. Plant traits will be measured to evaluate microbial effects. The biofilm-forming capacity of the microbial communities will be quantified using traditional crystal violet staining assays. Rhizosphere soil aggregates will be sampled for in situ microscopy analysis. Rhizosphere soil will be analyzed for metabolite profiles using solvent extraction and mass spectrometry. Furthermore, rhizosphere soil aggregates will be collected for relaxometry analyses to explore soil structure and water dynamics. The recruitment of two master’s students will contribute to the project. One (M2-AGRO, UMR Agroécologie), supervised by S. Jacquiod (coordinator), will manage the plant experiment. The other (M2-PAM, UMR PAM), under the guidance of P. Bodart (expert in relaxometry), will develop the relaxometry protocols. Microscopy and metabolomic will be done by service provision to the platforms. The collaboration will advance our understanding of how microbes reshape rhizosphere soil properties to benefit host plants, aligning with HARMI goals in WP1 and WP2.