Detection and evaluation of volatile and non-volatile antifungal compounds produced by Bacillus spp. strains

The identification of antifungal compounds produced by microorganisms is crucial in the context of sustainable agriculture. Bacteria of the genus Bacillus have a broad spectrum of action that can influence plant growth and control pests, vectors of public health relevance and phytopathogens. Lipopeptides are the main compounds related to the biological control of several pathogen species. Strains with biotechnological potential are identified by means of in vitro bioassays and molecular tests. In this study, strains from the Bacillus Bank of Brazilian Agricultural Research Corporation (EMBRAPA/DF/Brazil) were selected to control the fungal pathogens Scle-rotinia sclerotiorum and Fusarium oxysporum by pairing assays. The detection of genes for biosynthesis of anti-fungal compounds from strains with high pathogen-inhibition capacity was correlated with peptide synthesis, such as bacillomycin D, fengycin d, bacilysin and surfactin. Their gene expression in contact with the pathogen was analyzed by Real-Time PCR. The volatile organic compounds produced by selected Bacillus strains were identified and quantified. In co-culture assays, the inhibition zone between Bacillus strains and Sclerotinia scle-rotiorum was evaluated by scanning electron microscopy. Thirteen potentially anti-pathogenic strains were selected. Genes related to the synthesis of antifungal peptides were detected in 11 of them. In five strains, all tested genes were detected. Bacillomycin was the most frequently found lipopeptide gene. The fungus-bacteria interaction potentiated the production of volatiles. Several ketones and other volatile compounds with anti-fungal activity were identified. Relevant morphological changes in the fungus were observed when paired with bacteria. The study demonstrated the efficacy of the selected strains with regard to the biological control of phytopathogens and their biotechnological potential.