Cyclic lipopeptides from beneficial bacilli are interesting candidates to develop plant biocontrol solutions due to their antimicrobial properties and ability to stimulate plant immunity. The biological activities of CLPs are related to membrane-active properties with a mode of action mainly described as a detergent effect. We recently evidenced that the CLPs effect on membrane physical state is another key parameter to understand their biological activities and especially their ability to stimulate plant immunity. Therefore, the purpose of this proposal is to use X-ray scattering to gain unique insights in the structural effect of CLPs on lipid membrane, with a focus on three structural variants of surfactin showing distinct biological activities. Comparison of SAXS/WAXS data with biological results will deepen our understanding of the connection between membrane activity and biological properties of CLPs, a key milestone to rationally design and implement CLPs as biocontrol agents.