Lipopeptide culture filtrates from Bacillus spp. provide effective protection to wheat against the foliar pathogen Zymoseptoria tritici.

AIMS: Biocontrol products based on microorganisms and natural substances are promising alternatives to chemical pesticides that could contribute to develop a more sustainable agriculture. Here, we investigated the potential of cell-free culture filtrates (CFCFs) from two strains of the Bacillus subtilis group to inhibit Zymoseptoria tritici, a major fungal pathogen of wheat. METHODS AND RESULTS: Foliar application of CFCFs from Bacillus velezensis GA1 and Bacillus sp. III1 on wheat seedlings in a greenhouse strongly reduced Z. tritici disease severity (>90%). In vitro bioassays showed that CFCFs completely inhibited the spore germination and fungal growth (100%). In planta cytological investigations revealed a significant impact of the treatments on both spore germination (∼40% inhibition) and fungal growth of Z. tritici (>80% inhibition). High Performance Liquid Chromatography (HPLC) analysis showed that the Bacillus strains displayed different lipopeptide profiles. The CFCF obtained from Bacillus GA1 contained 90 mg l-1 of iturin A + surfactins + fengycins and the CFCF obtained from Bacillus sp. III1 contained 25 mg l-1 of mojavensin A (iturin family) + surfactins + fengycins. CONCLUSIONS: Strains of the B. subtilis group producing different iturins could provide several CFCF-based solutions for the biocontrol of Z. tritici.

The Diversity of Lipopeptides in the Pseudomonas syringae Complex Parallels Phylogeny and Sheds Light on Structural Diversification during Evolutionary History.

Pseudomonas spp. colonize diverse aquatic and terrestrial habitats and produce a wide variety of secondary metabolites, including lipopeptides. However, previous studies have often examined a limited number of lipopeptide-producing strains. In this study, we performed a systematic analysis of lipopeptide production across a wide data set of strains of the Pseudomonas syringae complex (724) by using a combined bioinformatics, mass spectrometry, and phylogenetics approach. The large P. syringae complex, which is composed of 13 phylogroups, is known to produce factins (including syringafactin-like lipopeptides), mycins (including syringomycin-like lipopeptides), and peptins (such as syringopeptins). We found that 80.8% of P. syringae strains produced lipopeptides and that factins were the most frequently produced (by 96% of the producing strains). P. syringae strains were either factin monoproducers or factin, mycin, and peptin coproducers or lipopeptide nonproducers in relation to their phylogenetic group. Our analyses led to the discovery of 42 new lipopeptides, bringing the number of lipopeptides identified in the P. syringae complex to 75. We also highlighted that factins have high structural resemblance and are widely distributed among the P. syringae complex, while mycins and peptins are highly structurally diverse and patchily distributed. IMPORTANCE This study provides an insight into the P. syringae metabolome that emphasizes the high diversity of lipopeptides produced within the P. syringae complex. The production profiles of strains are closely related to their phylogenetic classification, indicating that structural diversification of lipopeptides parallels the phylogeny of this bacterial complex, thereby further illustrating the inherent importance of lipopeptides in the ecology of this group of bacteria throughout its evolutionary history. Furthermore, this overview of P. syringae lipopeptides led us to propose a refined classification that could be extended to the lipopeptides produced by other bacterial groups.