Insights into the impact of global regulators on the produc􀆟on of bioac􀆟ve secondary metabolites of Bacillus velezensis

Bacillus velezensis is one of the most promising biocontrol agents used for protecting crops against microbial diseases in sustainable agriculture. This biocontrol potential lies notably in its ability to coproduce a vast array of bioactive secondary metabolites (BSMs) retaining strong antimicrobial activity or other key ecological functions. It includes multiple non-ribosomally synthesized (NR-)BSMs such as cyclic lipopeptides, polyketides, small oligopeptides and siderophores but also some terpenes and diverse ribosomally synthesized and post-translationally modified peptides (RiPPs). Thereby, understanding the regulation of B. velezensis BSMs synthesis is crucial to understand the regulation of its biocontrol activities. In the model species B. subtilis, BSM synthesis is mainly under the control of some global regulators (GR) also referred as pleiotropic or master regulators. We assume that similar rules apply for other species but our knowledge about such BSMs regulation is still very limited in plant-beneficial bacilli such as B. velezensis which differs in its lifestyle and forms a larger and more diversified panoply of compounds. In this work we aimed to draw a global picture of BSM regulation in B. velezensis. Using a reverse genetics approach, we assessed the impact of 14 GRs known to control developmental traits, multicellular behavior or responses to environmental cues. Our data highlight a central role of some regulatory elements such as quorum-sensing related ComA and sporulation regulator Spo0A for the modulation of BSM production. Moreover, cyclic lipopeptides and polyketides also appears differentially fine-tuned by additional GRs. Finally, it appears that each BSM has its unique regulatory scheme. We also observed species-specific roles of GRs such as CodY, involved in central metabolism regulation, which appears to have little impact on NR-BSMs synthesis in opposition to its major role in B. subtilis. Using the same approach, we assessed the impact of those GRs on antimicrobial activities of B. velezensis against a range a phytopathogens. This later experiment further highlights how GRs impact antimicrobial potential of B. velezensis.