Determining the Antifungal Activity of Bacillus Species Against Fusarium graminearum.

The Fusarium head blight (FHB) is caused by Fusarium graminearum (Fg) in cereals crops. The pathogen affects the spikelets producing symptoms with white chalky appearance and shrunken grains. Sometimes symptoms are not visible but the grains lodged with high levels of mycotoxins such as Deoxynivalenol. We wanted to determine whether biocontrol agents such as Bacillus could be used to control Fg. For this purpose, in vitro antagonism assays were performed with Bacillus subtilis strains including QST713, FZB24 and EU07 to assess the suppression of Fg. Plugs of Bacillus were placed in medium PDA/NA with a plug of the fungus and incubated for 4 days (28°C). Fungal growth was assessed by taking pictures and evaluating with a software. Fungal cultures without Bacillus plugs were used as controls. Similarly, assays were also performed with the cell-free culture supernatant of the bacteria that were grown in broth for 24, 48 and 72h. Supernatant was filtered through 0.22µm membranes and filtrates were used for antimicrobial activity. Filtrates (100µl) were normalised using Bradford assay, spread over the media, and one plug of the fungus was placed over the medium. The B. subtilis strain EU07 showed the highest inhibition of fungal growth in both plug and filtrate tests, followed by QST713 and FZB24. Currently we are carrying out comparative genomics of these Bacillus strains as well as transcriptomics on EU07-Fg interactions. Latest results will be presented.