Brevibacillus fortis NRS-1210 produces edeines that inhibit the in vitro growth of conidia and chlamydospores of the onion pathogen Fusarium oxysporum f. sp. cepae

Authors: Johnson, Eric; Bowman, Michael; Dunlap, Christopher

Submitted to: Antonie Van Leeuwenhoek
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2020
Publication Date: 4/11/2020
Citation: Johnson, E.T., Bowman, M.J., Dunlap, C.A. 2020. Brevibacillus fortis NRS-1210 produces edeines that inhibit the in vitro growth of conidia and chlamydospores of the onion pathogen Fusarium oxysporum f. sp. cepae. Antonie van Leeuwenhoek. 113:973-987. https://doi.org/10.1007/s10482-020-01404-7.
DOI: https://doi.org/10.1007/s10482-020-01404-7

Interpretive Summary: Onions are susceptible to several fungal pathogens that reduce yield and quality. Fusarium basal rot damages onions, as well as shallots and chives. We identified a bacterium that secretes antifungal compounds into the bacterium growth liquid. The antifungal compounds killed fungal cells that cause Fusarium basal rot in a few hours. Experiments also determined that the antifungal compounds were still effective in killing fungal cells after a heat treatment. The antifungal compounds were purified and identified as edeines, which have been studied by several laboratories. Edeines are capable of killing animal, plant and human cells in addition to fungal cells. Edeines might be useful as universal disinfectants provided that their toxic activity could be deactivated after use.

Technical Abstract: Onions can be damaged by Fusarium basal rot caused by the soilborne fungus Fusarium oxysporum f. sp. cepae (FOC). Control of this pathogen is challenging since there is limited genetic resistance in onion. The identification of molecules that inhibit this pathogen is needed. Antagonism screening showed Brevibacillus fortis NRS-1210 secreted antifungal compounds into growth medium. The spent growth medium, diluted 1:1, inhibited growth of FOC conidia after seven hours and killed 67–91% of conidia after 11 h. The spent medium also inhibited growth of propagules from F. graminearum, F. proliferatum, F. verticillioides and Galactomyces citri-aurantii. Full strength spent growth medium did not effectively kill FOC conidia and chlamydospores inoculated into a sand cornmeal mixture. In silico analysis of the B. fortis NRS-1210 genome indicated the biosynthetic clusters of several antibiotics. Fractionation of spent medium followed by reverse-phase liquid chromatography with tandem mass spectrometry analysis found that fractions with the most antifungal activity contained a combination of edeines A, B and F and no other recognized antibiotics. 1H NMR signals of the active fraction corresponded to edeine, a pentapeptide with broad spectrum antimicrobial activity which blocks translation in both prokaryotes and eukaryotes. Comparative genomics of Brevibacillus genomes shows edeine producers form a clade which consists of: Brevibacillus brevis, Brevibacillus formosus, ‘Brevibacillus antibioticus’, Brevibacillus schisleri, Brevibacillus fortis, and Brevibacillus porteri. This observation suggests edeine played an important role in the evolution and speciation of the Brevibacillus genus.