Abstract
Septoria tritici blotch, caused by the fungal pathogen Zymoseptoria tritici, is a highly significant disease on wheat crops worldwide. The objective of the present study was to find out new bacterial strains with bio-antimicrobial activity against Z. tritici. Two phyllospheric bacteria (S1 and S6) were isolated from wheat ears and identified as Bacillus velezensis strains according to 16S rRNA Sanger sequencing. Antagonistic assays performed with either living strains or cell-free culture filtrates showed significant in vitro antifungal activities against Z. tritici. For the culture filtrates, the half-maximal inhibitory dilution and the minimal inhibitory dilution were 1.4% and 3.7% for the strain S1, and 7.4% and 15% for the strain S6, respectively. MALDI—ToF analysis revealed that both strains synthesize cyclic lipopeptides but from different families. Interestingly, only strain S1 produces putative bacillomycin D. Such differential lipopeptide production patterns might explain the difference observed between the antifungal activity of the culture filtrates of the two strains. This study allows the identification of new lipopeptide-producing strains of B. velezensis with a high potential of application for the biocontrol of Z. tritici.
Highlights
Bacillus sp. are ubiquitous gram-positive bacteria occurring in diverse ecological niches and are known for their ability to produce a wide array of metabolites with applications in several areas, such as crop bio-protection against pests and diseases
We suggest that the antagonistic activity of the B. velezensis strains S1 strains of B. velezensis (S1 and S6), with very similar growth abilities in different nutrient media, and exhibiting significant in vitro antagonistic activity against Z. tritici
We suggest that the antagonistic activity of the B. velezensis strains S1 and S6 observed here against Z. tritici is due to the capacity of the strains to produce antimicrobial compounds, such as lipopeptides
Summary
Bacillus sp. are ubiquitous gram-positive bacteria occurring in diverse ecological niches and are known for their ability to produce a wide array of metabolites with applications in several areas, such as crop bio-protection against pests and diseases. 2021) but constitutes a phylogenetically incoherent group with two main reported clades (B. subtilis and B. cereus clades) [1]. Most of the exploited Bacillus species for the production of biologically active lipopeptides are B. subtilis, B. pumilus, B. licheniformis, B. velezensis, and B. amyloliquefaciens, the classification of these latter species is confusing and still not unanimous within the scientific community [2]. Bacillus species dedicate approximatively 5 to 8% of their total genome to synthesize bioactive secondary metabolites, such as peptides and lipopeptides, polyketides, bacteriocins, and siderophores [3]. Are synthesized by multi-enzymatic proteins named non-ribosomal peptide synthetases, which confer substantial structural diversity to the molecules and result in the production of linear, branched, or cyclic compounds usually considered as low ecotoxic compounds [4,5]. Lipopeptides are classified into three main families according to their amino acid sequence, including iturins
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