Abstract: A lot of environmental factors may modulate the production of antibiotics by plantbeneficial rhizobacteria in general and of lipopeptides by Bacillus in particular. Direct evidencefor an ecological role through the demonstration of an efficient lipopeptide production in situ isthus requested. This was the first aim of this study achieved by using an optimized HPLCcoupledelectrospray ionization MS that also allowed to compare the cLP profiles secreted bystrain S499 in the rhizosphere of different plants. Analyses of these root extracts revealed bothquantitative and qualitative modifications in the lipopeptide signature, suggesting that the rootexudate content may influence the synthesis of these molecules in a plant-specific manner. Thepossible impact of such variations in the cLP profile on the biocontrol potential of the producingstrain is discussed.