Identification of antifungal metabolites from a Streptomyces sp. effective against Fusarium graminearum and F. culmorum

Streptomycetes are gram-positive bacteria belonging to the phylum Actinobacteria, and the source of two thirds of all antibiotics in current clinical use. They are ubiquitous in soil, but can establish tight interactions with plants, producing a wide range of metabolites limiting pathogen development and promoting plant growth. Severe restrictions of fungicide registration and use in agriculture call for new and original approaches to manage plant diseases and mycotoxin contamination of food and feed, for example the use of biocontrol agents. During the research focused on the selection of Streptomyces spp. active against fusarium head blight and crown rot on wheat, we identified a promising strain able to limit mycelial development and deoxynivalenol (DON) production in infected grains. The strain DEF48 showed 45% and 65% inhibitory activity against F. graminearum and F. culmorum respectively using the dual-culture plate method, and limited up to 99% the DON amount in grains under microsilage conditions. Therefore, its antifungal secondary metabolites produced in vitro were characterized. Bioassay guided isolation was used to identify the metabolites by evaluating the activity of fractions obtained from agar plate extraction against the target pathogen. In addition, Illumina sequencing of its genome was performed. The integration of the antiSMASH bioinformatic analysis to identify secondary metabolite biosynthetic gene clusters, literature searches for antifungal compound composition, and the screening of the UV spectra of the active fractions allowed us to identify the candidate antifungal molecule. It represents a promising candidate to be employed in biological control of mycotoxigenic fusaria in cereals.