Lipopeptide-mediated antagonism: Modulation of Bacillus velezensis strain BE2 lipopeptides in response to Zymoseptoria tritici and Pyrenophora teres.

Bacillus species are emerging as alternatives to pesticides due to their antifungal properties, largely attributed to lipopeptide production. Our previous work demonstrated that Bacillus velezensis strain BE2 produces key secondary metabolites iturin, fengycin, and surfactin, which contribute to antifungal activity against Zymoseptoria tritici and Pyrenophora teres. This study investigated pathogen-specific modulation of BE2 secondary metabolites by tracking their production at multiple time points following co-inoculation with each pathogen. An overproduction of iturin, fengycin, and surfactin, along with siderophores and polyketides, was observed upon pathogen exposure. Difficidin levels remained unchanged in the presence of Z. tritici, while bacillibactin was unaffected by P. teres. Significant increases in metabolite levels were observed at three and five days post-inoculation, followed by a decline at seven days in pathogen-exposed conditions. Antagonism assays with purified compounds showed that fengycin strongly inhibited P. teres, while iturin was more effective against Z. tritici. Surfactin alone did not show antifungal activity but enhanced the efficacy of other lipopeptides and contributed to bacterial protection. Combination assays revealed synergistic effects between surfactin and iturin against Z. tritici, but not against P. teres, highlighting how strain BE2 modulates metabolite production in response to pathogens and underscore the potential of specific lipopeptides as antifungal agents against cereal diseases. This study provides valuable insights into the temporal dynamics of BE2's secondary metabolite production and its role in fungal suppression. It represents the first direct evaluation of the individual effects of CLPs on P. teres. These results support the development of optimized CLP-based formulations for sustainable plant disease management.