Mode of action of Bacillus spp. in the control of green mould of Agaricus bisporus

Abstract

Background: Bacillus species are widely studied as biocontrol agents given their competitive behaviour, ability to synthesise various antimicrobials and form resistant endospores. They represent an eco-friendly manner of crop disease control, including green mould of white button mushroom caused by several Trichoderma species. Objectives: The objectives of the study involved testing of the antifungal activity of Bacillus spp. cellfree supernatants against two Trichoderma spp. in vitro and detecting the lipopeptide biosynthetic genes in tested strains, with the aim of preliminary determination of the mode of action. Methods: Bacillus spp. supernatant activity against Trichoderma aggressivum f. europaeum T77 and Trichoderma harzianum T54 was tested by well-diffusion assay, in four replicates. Detection of four lipopeptide biosynthetic genes (sfp, fenD, bamC, part of the iturin operon) in Bacillus spp. strains was performed by PCR amplification. Results: Twenty-three Bacillus spp. supernatants inhibited the growth of T. harzianum T54 with inhibition zone diameters ranging from 16.1 to 25.9 mm while only seven supernatants induced inhibition zones of T. aggressivum f. europaeum T77 that ranged from 14.3 to 29.3 mm in diameter. Fifteen Bacillus spp. strains were positive for the presence of sfp, ten for fenD, nine for bamC gene and six for the partial iturin operon. Nine strains did not show any antifungal activity towards the tested pathogens, although three of them were positive for at least one lipopetide gene. The results suggested antibiosis as a possible mode of action for 24 out of 33 examined Bacillus spp. strains.