Characterization and evaluation of two Bacillus strains, SS-12.6 and SS-13.1, as potential agents for the control of phytopathogenic bacteria and fungi

• Total antimicrobial activity of two isolates of Bacillus sp. was characterized.
• The strains inhibit the growth of phytopathogenic bacteria in vitro.
• Very strong antifungal activity was confirmed in vitro and in vivo for both strains.
• Detected compounds belong to the class of antimicrobial lipopeptides.
• Mass spectrometry identified compound that corresponds to surfactin.

Two strains of Bacillus sp., SS-12.6 and SS-13.1, showed very strong antibacterial and antifungal activity against phytopathogens. The PCR analysis showed that both strains have the genes for biosynthesis of iturin, bacillomycin and surfactin. Kinetics of production of antimicrobial substances in these strains showed that synthesis started at the beginning of exponential phase of growth. Maximum of activity was slowly reached at the beginning of stationary growth phase and was maintained until the end of observed period. Ethyl acetate extracts of cell-free supernatants of both strains were particularly active against several postharvest fungal pathogens, in vitro and in vivo, in the experiment with apple fruits. Mass spectrometry analysis of ethyl acetate extract of the supernatant of strain SS-12.6 confirmed the presence of antimicrobial lipopeptide surfactin.

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